Pierre Gassendi

First published Tue May 31, 2005; substantive revision Tue Mar 19, 2024

Pierre Gassendi (b. 1592, d. 1655) was a French philosopher,scientific chronicler, observer, and experimentalist, scholar ofancient texts and debates, and active participant in contemporarydeliberations of the first half of the seventeenth century. Hissignificance in early modern thought has in recent years beenrediscovered and explored, towards a better understanding of the dawnof modern empiricism, the mechanical philosophy, and relations ofmodern philosophy to ancient and medieval discussions. While Gassendiis perhaps best known in history of philosophy for his disputes withDescartes, his relations with other major figures, including Kepler,Galileo, Mersenne, Beeckman, and Hobbes, represented even moreimportant transactions of ideas. And while Gassendi also sought tocommunicate anew the ideas of Epicurus, the Stoics, and other earlierthinkers, his resulting amalgam of perspectives provides a modern viewof his own making, one of the touchstones of philosophy and science inhis times: our access to knowledge of the natural world is dependenton the constraints and licenses that follow from our epistemic graspbeing limited to information provided by senses. Through thisarch-empiricism—tempered by his priestly adherence to keyelements of Church doctrine—Gassendi views metaphysics as arealm for speculation grounded in the possibility of empiricalconfirmation, logic as (by turns) a psychologistic and probabilisticenterprise, knowledge of the external world as built on and foreversubject to sensory-based evidence, and ethics in quasi-hedonist,possibly quantifiable terms. Gassendi’s philosophy is a constantreview of other sources, a thorough consideration of the landscapeinto which his own empiricism fits and represents an alternative tocontrasting claims, past and present. What is sometimes thought of aseclecticism—particularly in the posthumous masterwork, theSyntagma Philosophicum—actually recasts philosophy as afully-referenced scholarly enterprise, advancing historical styles andrhetorical modes in philosophical research and exposition. In thesechanges he matches even the magnitude of innovation that marks hisatomist matter theory, empiricist perspectives, explorations anddefenses of the new physics, objections to theMeditations,and refutations of contemporary Aristotelians and mystical thinkers.It has been argued—perhaps unfairly—that Gassendi’score ideas are better preserved through the medium of writings byBoyle, Locke, Huygens, and Newton. Yet his presentation of anempiricism, atomism, and new cosmology in historical and philosophicalcontext greatly advanced the community of scholarship in his day, andrepresents what was then a fairly new model of research andexposition—still in philosophical use today.

1. Historical Background and Gassendi’s Life

Born in 1592 to a family of commoners in the tranquil Haute-Provencetown of Champtercier, Pierre Gassendi rose to become the greatestProvençal scholar of his day, a member of the preeminent Frenchintellectual group of his times—the Mersenne circle—andprofessor of mathematics at the College Royal. At an early age, hisinstructors recognized great potential, and dispatched him at agesixteen to Aix-en-Provence for studies of further sophistication thanhis local schooling could provide. In these first years of scholarlypursuit, Gassendi shuttled between Aix and Digne (the provincialcapital) and so began a life-long pattern of itinerant travel. Hisextensive and early education vaulted him to professorship at Aixwhile still in his mid-twenties. He shuttled between careers as well,attaining success and station not only in academic circles but also inthe Catholic Church.

Gassendi’s career as a priest is a crucial facet of hisintellectual constitution: his writings reflect an unbendingallegiance to Holy Scripture and Church teachings, though notnecessarily in orthodox doctrinal lights. He was ordained at the ageof 24 or 25 and, while there is no question of the strength of hisfaith, one motivation for his career in the Church appears to be itsprovision of a sinecure. Thus Gassendi started at the rank of alow-level local official (Chanoine of the Cathedral) in Digne and roseto the rank of a slightly higher-level local official(Prévôt), still in Digne, some twenty years later. Thoughhe clearly pursued a studied relationship with his higher authority,all the while he wrote letters of support to the Church-embattledGalileo, sought appointment to the secular College Royal, andcultivated deep personal and intellectual ties with his non-Churchpatrons—the affluentfonctionnaire, Francois Luillier;the Provençal savant, Nicole-Pierre Fabri de Peiresc; the localcount of Alais, Louis Emmanuel de Valois; and the Parisian noble,Habert de Montmor.

After some years of instructing pupils in philosophy and theology,Gassendi distanced himself from what he believed to be rigid teachingsof the Scholastics in hisExercitationes Paradoxicae of 1624.Thereafter he began a formative partnership in physiological,astronomical, and historical studies with the wise and wealthyPeiresc, summarized in Gassendi’s glowing biography written uponPeiresc’s death in 1637. By this time, Gassendi had alsodeveloped his early interests in a variety of questions in basicphysics and in restoring the philosophy of Epicurus—much asThomas had restored Aristotle, integrating his thought with what heheld to be theologically viable. His published work in philosophy andnatural philosophy captured the attention of the Minim priest, MarinMersenne. Gassendi spent the last two decades of his life travelingback and forth between Provence and Paris because of varyingcommitments to patrons, appointment to the College Royal, and illhealth. Throughout, he remained informed of and involved withscholarly discussions of the day, owing to his engagement with thegroup of philosophers and scientists united through correspondencewith Mersenne. In the Mersenne circle, debates ranged over numeroustopics central to the dismantling of Aristotelian and Scholasticworld-views, and Mersenne often used his role as facilitator to bringtogether opponents on these issues. In that context, Mersenne helpedenable the entry of Gassendi’s criticisms of Descartes’sMeditations into theObjections and Replies(Gassendi subsequently published his rebuttals in hisDisquistioMetaphysica of 1646) and focused Gassendi’s attention onrefuting the mystical attacks on Kepler by Robert Fludd(Epistolica Exercitatio, in qua principia philosophiae RobertiFluddi medici reteguntur, 1630). Members of this circle regularlyreported on each other’s experiments and proposed newchallenges, such as Poysson’s well-known puzzling over whetherphysical indivisibles could or should be identified with mathematicalpoints. Gassendi used this forum to learn about other empiricalstudies as well as to work out a good many of his views.

His scientific career was varied and complex, if never quiteassociated with glowing triumph. Some historians consider his greatestaccomplishment in this sphere to be his contribution to the revival ofancient atomism but this represents only one end of hisanti-Aristotelian physics, and a small, albeit core element of hisscientific interests. His other accomplishments in physics includes astudy of bodies in free fall (closely modeled on Galileo’swork), a mature enunciation of the principle of inertia, and an earlyand reasonably accurate interpretation of the Pascalian barometryexperiments of the late 1640s. Gassendi also ventured intoexperimental science: he attempted to measure the speed of sound bycannon fire, arranged to have weights dropped from the mast of amoving ship to enact Galileo’s thought experiment (and so dispeldoubts about the motion of the Earth), and conducted numerous chemicaltrials involving, among other things, the dissolution of salts andformation of crystals (which he took to bolster his molecular theoryof matter). These are only some of his better-known exploits. Inaddition, he offered a wide variety of speculations on the earthsciences based partly on geological fieldwork and biological andphysiological observations—and as shaped by his atomisthypothesis. Finally, Gassendi devoted much of his time to astronomicalpursuits. He made regular observations of the skies for decades,producing confirmatory evidence for Kepler’s views, observingsunspots, the anses of Saturn, and the passage of Mercury before theSun (1631), and successfully predicting an eclipse in 1654. Moreover,he commissioned the first map of the moon, defended the Copernicanview as plausible save for its conflicts with Church teachings, andoffered many disparaging words on what he considered the scurrilousand empirically intolerable practice of astrology.

In his final years, Gassendi relented to pressure from friends andreleased a major portion of his Epicurean studies to the public,publishing his Latin translation of Diogenes Laertiius’s Book Xon Epicurus, along with ample commentary, in hisAnimadversiones of 1649. He continued to work on thisinterpretive material, however, steadily incorporating philosophicaland scientific insights, until his death in the Paris apartment ofMontmor in 1655. Montmor, acting as executor, collected this materialin manuscript form and with Gassendi’s other Parisian friendsarranged to have it published as the posthumousSyntagmaPhilosophicum. TheSyntagma is more systematic than theAnimadversiones, largely eschewing the sometimes philologicalcharacter of the earlier commentary and principally discussing logic,the natural sciences, psychology, and ethics from the perspective ofwhat Gassendi deems philosophically, historically, and theologicallysupportable. His interests in Epicurus are ever-present, not least inthe structure of the work, which is divided into a Logic (includinghis textbook-formatInstitutio Logica), Physics, and Ethics.Happily, we have a rather well-rounded picture of Gassendi’sintellectual pursuits, on top of his Epicurean projects. Montmor andcompany had the good sense to bundle theSyntagma togetherwith the better part of Gassendi’s other writings (theAnimadversiones notably excepted) in six volumes of collectedworks, theOpera Omnia (Lyon, 1658; Florence, 1727), whichincludes as well earlier letters on optics and the free fall ofbodies, a portion of his voluminous astronomical observations, and agreat deal of his correspondence.

(In what follows, we citepassages inOpera Omnia by using the following abbreviationsfor the volumes: “O I”, “O II”,…,“O VI”.)

In the wake of Gassendi’s death, his general renown, influenceon French schooling and popular conceptions of natural science, andrivalry for Descartes’ legacy, all grew. This impact wasenhanced by the 1674–1675 publication of a condensed, abridged,reorganized, and occasionally paraphrased version of theOperaOmnia, written in French by Gassendi’s acolyte,François Bernier. Over the following half century, the“Gassendistes” stood as formidable opponents to the“Cartésiennes” in French debates over educationaland scientific matters, and Gassendi’s thinkingspread—variously influencing Leibniz, Boyle, Locke, and Newton,among others.

2. Method and Nature of Philosophical Inquiry

Commentators and historians conventionally designate Gassendi as anearly modern thinker yet there is good reason to at least consider hiswork as belonging to the tail end of the preceding period. One facetof his work that closely resembles Renaissance philosophy and scienceis the historical focus of his method of inquiry. For almost everyphilosophical issue Gassendi deems worthy of discussion, he firstintroduces a wide range of previous competing views, beginning withthe antique schools, which he considers as ‘live’ options.He engages with Aristotle and early (as well as late) Aristotelianism,and allows great debts to Skeptic, Stoic, and Epicurean thought. Thehistory of philosophy is for him a source of vitally importantreasoning, the generally correct way to frame our questions, and moreoccasionally, the answers to those questions. Thus one principalattraction of atomism for Gassendi is that it suggests a way to thinkabout causation among material objects which he finds an attractivealternative to Aristotelian views on one hand and non-physicalistviews on the other. In his theory of knowledge we find one moreinstance of using ancient frameworks to model contemporary problems:no criterion of truth, for example, is adequate unless it satisfiesthe standard points made by the classical Skeptics. Some may see thisas evidence of Gassendi’s modernism, but his broad concerns withSkeptical thought certainly place him among good Renaissance company.(The Skepticist and anti-Aristotelian strains of his Exercitationesare also thought to be influenced by his reading ofnear-contemporaries, including Juan Luis Vives and PierreCharron.)

Another Renaissance-type element of Gassendi’s writings is hisstylistic obsession with antiquity. His Latin is learned if a bitstultified, rife with quotations from Virgil, Horace, Cicero,Tertullian, and others. An embroidered, ornate quality marks his fewextant French writings, too. He quotes frequently and liberally fromclassical sources, usually in Latin though sometimes in Greek, and histranslation of Diogenes Laertius’s Book X on the life ofEpicurus is the centerpiece of his 1649Animadversiones.Gassendi does not, as does Descartes, suggest his work is so modern asto have been inventedde novo. Rather, he constantly refersthe reader to a wide variety of other, generally classical writers assources of both like-minded and conflicting perspectives. Finally, thesingle most time-consuming project of his career consists in hisprodigious efforts towards reviving the works and reputation of oneparticular classical figure, Epicurus.

These Renaissance trappings notwithstanding, there are also at leasttwo reasons to think of Gassendi as very much among the moderns. Forone, he embraces the new empiricist’s assessment of the oldscience: what is wrong with the Aristotelians’ physics is itsroutine presentation, as well as grounding, inaprioritheoretical claims. He is not the only, or the first author of such aview. Galileo breaks with tradition in distinguishing a science ofmotion that, in principle at least, makes use of observation andexperiment. Bacon and Descartes, for their part, also counsel (tovarying degrees) a scientific method which builds on experientialknowledge. But among thesavants of the early seventeenthcentury, only Gassendi, whose awareness of empiricism’s rootsand implications is evident across his intellectual pursuits,integrates philosophy and science on what he believes to be strictlyempiricist grounds. This integration is a natural consequence of hissuggestion that we gain all knowledge—outside of thetheological—from the senses.

A range of equally modern views follow from his proposed empiricistfoundations for the new science and its methods. He suggests aprobabilist notion of what counts as warranted empirical belief, andinsists that we may license beliefs about the sub- andsupra-perceivable but only if they are well-grounded in our beliefsabout the perceptually given. Further, he devises rules for acceptingor rejecting hypotheses, and guidelines for directing empiricaldiscoveries and our judgments of the same, where all such claims aresubject to the test of evidence from experiment or observation. It isfar from true that all, or even most, of his own claims about thenature of the physical world meet this test, but the modernity ofGassendi’s philosophy and science lies in his proposal that thisis a goal to be set, altogether.

3. Refutations of Aristotelians and Descartes

For many commentators, Gassendi’s empiricist theory of knowledgeand objections to Descartes’sMeditations count as hisparamount philosophical contributions. In his core epistemology, heoffers the first modern model of knowledge from the senses to beintegrated with a physiological account of perception. In hisobjections to Descartes, he rejects the clarity and distinctnesscriterion, seeks to undermine the reasoning behind thecogito, and assails the ontological argument. Each of theseviews represents a battle Gassendi has taken up against theAristotelian tradition or the Cartesian stance; his thoroughgoingempiricism poses an alternative to both of these competingperspectives.

One cornerstone of Gassendi’s anti-Aristotelianism is thesuggestion that there is nothing necessary about the way the world is.God, he proposes, could have made the world work in any number ofways, and the contingent history and character of Creation means thatthere is nothing immutable about the essence of a material thing.(That a ‘substance’, in either the Aristotelian orCartesian sense, might have an immutable essence, is a differentmatter, and insofar as Gassendi has such a notion (for example, withrespect to space, time, matter, and void) he agrees that such thingsfeature unchangeablesine qua non characteristics.) Moreover,Gassendi maintains, regardless of whether there are any essences andwhether they might be mutable, there are none to which we have anyepistemic access. The sole originating source of our knowledge is theinformation the senses provide, such that what we know is closelylinked to what we can perceive. However, as Descartes notes, we canperceive only appearances. Gassendi draws from this point the veryuncartesian lesson that appearances are all we can know about,too—thereby ruling out knowledge of unperceivable essences. Oneline of this reasoning can be found in his discussion of classicalskeptical tropes concerning the relativity of evidence from the sensesto individual experience—that honey tastes sweet to me, thoughbitter to you; and that fire seems hot to us, though not so to insectsthat live near fire (O III (DM) 388b; R 535). Since differentpeople have distinct experiences, our knowledge of honey’s tasteor fire’s heat differs from person to person and thus is not areliable guide to invariable characteristics of, for example, thehoney or fire. In cases like these we know a thing’s qualitiesonly as we record them on a subjective basis. Such sensoryinformation, based on experiences which vary intersubjectively, cannotyield judgments about a thing’s qualities which do not vary inthat (or any other) way. Hence we lack knowledge of the thing’sessence, if indeed there is one. More broadly, from our principalsource of ideas—the senses—we know only how things appearto us (O III (DM) 311b-312a; R 184). (If we are to haveknowledge of an object’s essence, Gassendi proposes, suchrequires a “perfect interior examination” of that object,which is apparently not something we may gain from empiricalstudy.)

Gassendi also contests the Aristotelian view that we can knowuniversals, on the grounds that we cannot perceive anything more thanparticulars in the world (O III (Exercitationes) 159a; EP280–281). It follows, he suggests, that neither can there be anyuniversals we know about, at least with anything like certainty. Somecommentators (including Bloch, Rochot, and Osler) propose thatnominalism is a central Gassendist view, on the basis of thisrejection of essences and universals, as well as his epistemicreliance on the apparent, and interest in signs and their conventionalcharacter. But Gassendi’s nominalism—if it be such, in theorthodox sense—is intended less as an ontological assessment,than as a statement of the limits of human mental capacity, whetherepistemic or linguistic.

Further building on the insistence that all knowledge comes from thesenses, Gassendi discusses the view (shared as well by Descartes andthe Aristotelians) that there are propositions we can know withcertainty. Since all propositions are judged as true or false on anempirical basis, none can be deemed indubitable, save those oftheology and theologically-derived cosmology. This lack of certaintyextends as well to logical demonstration, whether of inductive ordeductive character. Nothing is certain about such demonstration,Gassendi suggests, save the limits imposed upon it by the frailty ofhuman intellectual capacities. The natural bounds of our epistemicgrasp in the physical sciences, astronomy, or most any other field ofstudy is just what the senses tell us, plus any correctives reasonsupplies on the basis of sensory-based knowledge we have alreadyaccrued.

That Gassendi thinks there is a need for correctives on sensoryinformation makes clear the depths of his rejection of epistemicfoundationalism in Aristotelian or Cartesian thought: we cannot trusteven information from the senses to give us a failsafe picture of theworld. In this he embraces the Skeptical judgment that no source ofbelief can provide for certain knowledge. Yet he cannot accept theirwholesale dismissal of sensory-derived evidence for belief. Knowledgefrom the senses is possible just in case we have warrant for judgmentsabout appearances, though we may lack warrant for certainty aboutthose judgments. To the limited extent that we have the second sort ofwarrant, he suggests, we find this in the reliability of our sensoryapparatuses (as he describes in his Epicurean-inspired account ofperception). We see here a ‘constructive skepticist’response to the Skeptics who say no knowledge is possible and to thoseancient and latter-day ‘dogmatic’ thinkers (including, inhis view, the Aristotelians and Descartes) who say knowledge involvesthe attainment of certain belief—and is readily attainable.While it may not be possible to have certain beliefs, it is quitepossible to have knowledge given that we construe it as justified butless-than-certain belief. (Naturally, it must have a veridicalcharacter as well, and Gassendi thinks it sufficient that such beliefsare at least truth-resembling.)

Gassendi articulates such disagreements with Descartes in theObjections, where he also rejects the Cartesian criterion of clarityand distinctness, as either a standard for judging ideas or source ofepistemic warrant. As regards the former, Gassendi points out thatreason, which comprises our intellectual judgments and interpretationsof sensory information, is itself prone to error:

…although deception, or falsity, is not to be found in thesenses themselves, which merely behave passively and only reportthings as they appear and as they must appear given their causes, itis to be found in the judgment, or mind, when it does not act withenough circumspection and does not perceive that things which aredistant…appear more indistinct and smaller than they do closeup…. (O III (DM) 388a; R 532; B 266–267)

If, for all their faults, claims based on sensory information are morereliable than those based on reasoning (about sensory information oranything else), then we ought not appeal to the latter as a basis forjudging among claims of the former. One reason he thinks sensory-basedclaims are the more reliable of the two is that he takes the senses topassively (hence steadily) collect information, in contrast to ourmental judgment actively (hence irregularly) organizing or relatinginformation. This is not to say that we will have no problems gaugingthe warrant for claims based on sensory information as we collect it.Rather, we will have even more problems in gauging claims based onideas about sensory information after such ideas are that much moreremoved from a direct and perspicuous relationship to the world asexperienced, in our organizing and relating them to other ideas.

Moreover, the Cartesian criterion is irrelevant to judging cases ofempirical knowledge, Gassendi suggests—and even if thiscriterion were not irrelevant, Descartes’s own claims toknowledge should fail all the same. First, in the case of empiricalknowledge, Gassendi proposes that the Cartesian criterion fails onclassical Skeptical grounds: it is possible for us to have ideas fromthe senses we take to be clear and distinct which are nevertheless notthe basis for warranted claims to empirical knowledge of a generalnature. Though we may have clear and distinct ideas about theappearances of, for example, the color of the sky we perceive, wecannot infer from this clarity and distinctness that we know whatcolor the sky is. As the Skeptics warn, the sky could appear todifferent persons in different colors, and as Gassendi adds, our ideasof such an appearance could each be clear and distinct (O III(DM) 314b; R 198–199). Second, knowledge claimsDescartes takes to be demonstrated by reason alone Gassendi dismissesas anyway failing the proposed criterion; they are partial andconfused, he suggests, because they lack the immediacy characteristicof judgments we attain by strictly empirical means. Whereas ideas wegain from the senses directly represent worldly objects and events,ideas we attain by deductive proof are but hypothetical analogues tosuch sensory-derived ideas:

…it is not the same thing for us to conceive something by averitable idea or a true image, and to conceive that thing by aconclusion that follows necessarily from an anterior hypothesis. Inthe first case in effect we conceive of the thing as absolutely so; inthe second, that it should be some such thing; and also in the firstcase we know the thing distinctly and as it is in itself, and in thesecond case we know it only in a confused manner and by analogy, thatis, in referring to it as something that must be known by way of someidea (O IIIDM) 322b; R 234).

In brief, our reasoned claims are less than fully clear or distinctbecause we arrive at them through the mediation of ideas about ourempirical knowledge. Hence Descartes’s most cherished claimsabout essential properties of mind, God, and matter fail his owncriterion for lack of direct foundation in our ideas from thesenses.

Not all of Gassendi’s criticisms of the Cartesian criterion arerooted in his advocacy of knowledge from the senses. Thus, hesuggests, one other problem with that criterion is its failure to makegood on its foundationalist promise. Just in case some of our clearand distinct ideas turn out to be wrong, we will require some furthercriterion to distinguish them from the correct ideas. And if the newcriterion is simply something like ‘more clear and moredistinct’, then we are on the road to infinitely manyhigher-order criteria, which defeats the aims of the foundationalistproject altogether. Finally, Gassendi offers what Descartes himselfcame to call “the objection of objections.” Our ideasbeing clear and distinct ideas is perfectly consonant with asolipsistic perspective, but then the only thing we can know withcertainty is our own thoughts. Yet a viable criterion should (a) alsodistinguish our knowledge claims about the external world, and (b)mark solipsistic claims as dubitable to begin with. On top of theseobjections, Gassendi proposes that Descartes has put the cart beforethe horse by suggesting we can readily recognize what is clear anddistinct and use this as a guide to what is indubitable when what weneed in the first place is some guide as to what is clear anddistinct:

…the difficulty is not, as it seems, to know if one mustconceive things clearly and distinctly so as not to be mistaken atall, but to know by what way or method it is possible to recognizethat one has a conception so clear and so distinct that it is true andimpossible that we are mistaken. (O III (DM) 372b; R 458)

Another well-known set of Gassendi’s objections targetDescartes’ views of mind and body. One such objection is aprelude to the well-known puzzle over how mind and body could bethought to interact, posed by Princess Elisabeth of Bohemia. Gassendiwonders how Descartes could take the mind to be thinking substancelacking extension yet claim that it is somehow attached to the body,given that anything joined to a body must itself be extended (O III(DM) 399b-401a; R 584-590). Descartes’s answer is thathe does not take mind and body to be attached, which responseimmediately invites Princess Elisabeth’s puzzle.

In a related vein, Descartes’scogito reasoning alsoundergoes close scrutiny. Gassendi understands this reasoning as oneperson’s inference from his or her indubitable recognition ofcognitive activity, to the claim that he or she exists as the selfsameseat of such activity. Against such an inference he points out thatrecognition that one has a set of thoughts does not imply that one isa particular thinker or another. Were we to move from the observationthat there is thinking occurring to the attribution of this thinkingto a particular agent, we would simply assume what we set out toprove, namely, that there exists a particular person endowed with thecapacity for thought (O III (DM) 289a-290a; R 82-86).Descartes is in dangerous waters at this point, for if indeed the onlyclaim that is indubitable here is the agent-independent claim thatthere is cognitive activity present, then he can be fairly associatedwith Averroist panpsychism, and its considerable taint. At a minimum,the argument requires a significant leap of reasoning, and forGassendi, this is further evidence that Descartes places altogethertoo much faith in his criterion and the work he thinks it can do.

That Gassendi is primarily concerned here with the character ofDescartes’s reasoning is plain enough: in the end and broadlyspeaking, the two are actually close in their views about mind andbody. They are both dualists of one stripe or another, and theparticulars of Gassendi’s physically-rooted psychology arereasonably similar to those of Descartes’s model.Gassendi’s model of the mind is often taken to be whollymaterialist in design, particularly as seen through the prism of hiscritique of Descartes. Yet only one facet of the Gassendist soul isthe material anima, the locus of physically-determined pleasure andpain. He also posits an immaterial animus, the seat of the intellector rational understanding. This cognitive faculty is the locus ofspiritually-determined pleasures and pains we associate with, forexample, love of God or fear of evil. Here we have an echo of theThomist interpretation of De Anima, according to which vegetative andmotive facets of the soul perish with the body though an intellectivefacet lives on forever.

Elsewhere on a theological plane, Gassendi shares other core viewswith Descartes, though some commentators have tried to paint Gassendias concealing atheist tendencies, owing to his suspected materialistand libertine allegiances. Such a charge is inaccurate. Yet it is alsoso that Gassendi does not accept the Cartesian route to belief in theDivine, notably rejecting Descartes’ version of the ontologicalargument.

The Cartesian version of Anselm’s traditional argument suggeststhat God has the intrinsic property of existence as part of a divineessence, in the same way a triangle has intrinsic properties such ashaving three internal angles summing to 180 degrees. Further, as withall divinely-held properties, God has that existence property as aperfection—that is, God exists in a perfect way, such that Godcannot not exist. Gassendi rejects this reasoning on two grounds.First, we have no irrefutable intuitions of essences, whether such aresupposed to be represented by properties of triangles or of God.Descartes’ particular misstep here is to suggest that we maymove from the definition of God (which we intuit as a clear anddistinct notion) as essentially entailing the property of existence,to the view that there is such a thing as God with said property. Adefinition of a thing as having such and such properties does notcommit us to the thing existing with those properties, even if one ofthose properties is said to be existence. This much was noted inGaunilo’s early criticism of Anselm’s version. Yet themore general point Gassendi makes is that no intuitions untested bysensory experience will yield knowledge of God’s essence oranything else, as the primary mode of attaining knowledge (and that bywhich any intuitions must be tested) is empirical demonstration.Second, presaging the Kantian criticism, existence is neither aperfection nor any sort of property or predicate of things that exist.Rather, existence is simply an aspect of things that exist, the modeor state of being that describes its existing. Existence isaccordingly a precondition for bearing perfections (and forperfections being borne by the thing), rather than something whichitself can be a perfection. If we refer to a thing’s existence,we are only referring to a fact about the thing, that it exists.Rejecting the ontological argument, then, eliminates a sort ofconceptual confusion: although we might think of perfections existing(in a thing), it is hard to conceive of what it would mean forexistence to exist (in a thing), or for that matter, to not exist.Along similar lines, there is no reason to accept the underlying claimof the ontological argument that things which do not exist are eitherimperfect or lacking in any way (O III (DM) 379b-380b; R490–6).

4. Empiricism and Scientific Method

Another significant difference between Cartesian and Gassendist viewsof God is that for the latter there is no divine epistemicguarantor—indeed, for Gassendi, there is no absolute ornecessary guarantee on our epistemic access altogether. There is onlythe contingent warrant of the senses. In the textbook account of theearly modern debate among empiricists and rationalists, Gassendi playsa bit part in promoting the senses as the ultimate source of ourworldly knowledge. His views are painted as a vanguard but ultimatelyinconsequential Continental counter to Descartes and as a slightinfluence on Locke’s more ‘mature’ empiricism.Gassendi’s contribution is more noteworthy than all that,however. His theory of knowledge explicitly addresses historicaltraditions in epistemology, develops a proto-reliabilist theory ofepistemic warrant, wrestles with timeless difficulties of empiricism,and forms the basis of a set of allied views on the nature ofscientific investigation.

The need for a theory of empirical knowledge in Gassendi’s viewstems from the inadequacy of past and contemporary responses to theSkeptics, whose puzzles he finds particularly compelling in the formof the tropes as presented by Sextus Empiricus. The Skeptical tropescall our attention to the general problem of whether, given thefallibility of the senses,any knowledge is possible and inwhat the warrant for such would consist. Gassendi turns the problemaround, limiting its scope to finding warrant for empirical knowledgeand declaring the special solution to resolve the general case. Hissignificant move in this regard is to propose, against the Stoics(and, as we have seen, Descartes), that it is not a necessarycondition of our knowing some claim that we be certain of it. Thisprobabilism immediately broadens the range of what we can know throughthe senses—as does his suggestion that we include among suchclaims to knowledge those assertions about what may be hidden to thesenses yet legitimately inferred from evidence of the perceptuallygiven. This is his theory of sign-based inference, which suggests suchinferences are legitimate just in case they would be agreed to by agreat enough number of experts giving testimony—or else would befalse only on pain of contradiction.

Following an Epicurean, physicalist model, Gassendi recommends thatSkeptical worries are satisfied by truth-criteria and elements ofepistemic warrant rooted in the regularity and reliability of oursensory perception and formation of ideas. Trustworthy evidence fromthe senses yields warrant for empirical beliefs, albeit withoutcertainty and just in case the evidence for them does not conflictwith accepted evidentiary experiences. These claims are built upon theproposals that sensory information has a material form (in the case ofvision, Gassendi promotes an atomist theory of effluxions bearingimages or light from the viewed object to the viewer), that the mindreceives sensory information through a wholly physical process, andthat some cognitive faculties dependably allow us to detect truthproperties of the objects of knowledge. The physical processunderlying this perceptual account is inspired by Epicurus but thephysiological details, optics of light transmission, andepistemological lessons are strictly Gassendi’s own. Indeed,this account of justification marks him not merely as a proponent of acausal theory (as may be said of Descartes, relative to the divineepistemic guarantor) but as an early champion of a reliabilistapproach to the causal processes, claiming them as the source ofepistemic warrant.

The negative side of Gassendi’s theory of knowledge bows in thedirection of the classical Skeptics: we cannot be conclusively certainabout, nor find ultimate truths among, empirical beliefs. The positiveside rejects an absolute Skeptical doubt, however, suggesting thatempirical knowledge is possible because we can identify a range ofstrengths that are normally associated with many beliefs aboutappearances—their reliability, approximation to the truth, andlikelihood by degrees. This approach—what Popkin calls thevia media of Gassendi, the ‘constructive’skepticist—suggests a practicable if approximate understandingof the world is within our grasp.

This adumbrated version of empiricism is not without difficulties, asGassendi is first to recognize. For one, having extended the warrantfor the directly sensed to the indirectly sensed, we must find a wayto confidently adduce evidence on behalf of what appears before thesenses in indirect fashion only. For another, the supposition thatsolving for empirical knowledge presents a solution for all knowledgeintroduces the challenge of accounting for at least two apparentcounterintuitive instances—knowledge of abstracta and knowledgeof God and the cosmos (Gassendi subsumes the former to empiricalknowledge on proto-Millian grounds, but exempts most theological andcosmological truth from empirical grasp (O II 398–424,440–42)). Finally, he calls our attention to the recursivenature of empiricist doubts. If a lack of adequate sensory data stripsaway warrant for knowledge of the world then an empiricist theory ofknowledge must also appeal to what the senses tell us, about what wecan know of the world. The challenge, then, is to fashion anempirically adequate theory of acquiring sensory data. In formulatingsuch an account, he anticipates crucial elements of later reliabilisttheories of warrant.

On the basis of these global views of knowledge in general, Gassendidevelops elements of a theory of knowledge and method specific to thescientific endeavor. These elements include the proposal that weattain and justify empirical claims with the greatest warrant bydeduction—yet those claims are at root probabilistic. He furtherproposes that we maintain hypotheses as the basis of scientificreasoning so long as there is empirical evidence for them, howeverbroadly construed. Taken together, these elements constitute acommitment to a hypothetico-deductivism (H-D) which is characteristicof some instances of actual scientific reasoning that Gassendidiscusses. This is not a typical or modern species of H-D method,however, firmly wedded as it is to his empiricism. Indeed,Gassendi’s method cannot be adequately characterized in itsentirety in this fashion, given the severalother forms ofnon-deductive inference that he endorses or makes use of asfundamental to his scientific method, including sign-based inference,analogous reasoning, and inference to the best explanation.

A further element of Gassendi’s scientific method consists inhis appeals to indirect evidence for claims about the unobservable,and his willingness to count such evidence as adequate empiricalgrounds for maintaining viable hypotheses. The most prominent instanceof this strategy is his embrace of an atomist matter theory as a‘most likely hypothesis’. Of necessity, any evidence onbehalf of this hypothesis is to be found in the indirect form of‘indicative’ signs—these are the surface levelphenomena for which he takes the existence of atoms to be asinequa non condition. A paramount instance of such evidence in hisview is what we may see through the microscope, when the visualphenomena are explicable only given the existence of themicro-structures we perceive—and in turn those are explicableonly in terms of yet smaller structures. Gassendi maintains that themicroscopic observations of crystalline formation and dissolutiondemonstrate the molecular structure of matter, a key aspect of hisatomism. Equally innovative is his appeal to this putative source ofwarrant in support of his matter theory.

Such arguments for atomism highlight Gassendi’s anticipation ofthe modern notion of inference to the best explanation (IBE) as ameans of judging among competing hypotheses. In advancing thisstrategy, he emphasizes the capacity of a given hypothesis to accountfor a range of different phenomena as a guide to the degree to whichthat hypothesis approximates the truth. This strategy for justifyingclaims about atoms also reaffirms his reliance on empirical data inseeking confirmation of claims regarding the evident and nonevidentalike. While much is untenable or unlikely about these views, Gassendihas at least offered a set of proposals towards resolving one ofempiricism’s more vexing questions—how to transcend thebounds of sensory data. We can know about unobservables like atoms, heproposes, just in case our empiricism advances scientific knowledgethrough hypothetical reasoning and warrants the sorts of inferencesabout physical phenomena allowing for unseen features of theworld—for which the sensible features can provide evidence.

5. Atomist Matter Theory

The core of Gassendi’s mature philosophy and natural philosophyis his atomist matter theory. He initially borrows on historicalatomist sources—primarily Epicurus—but quickly integratesa range of atomist claims into his proposed empirically defensiblecomplex of physical, metaphysical, and ethical perspectives. Someaspects of his atomism fit poorly with the mechanical philosophy it issupposed to exemplify. Yet Popkin is correct in suggesting thatGassendi’s atomism is a premier instance of his philosophicaland scientific pursuits constituting one and the same project. Theputative empirical support does not stand up to close inspection, andhis particular brand of this matter theory is inconsistent with otherelements of the mechanical philosophy. Nonetheless, his atomismprovides an innovative and consistent model for micro-level accountsof macro-level physical structures and their behavior, throughout allmanner of natural, psychological, and social domains. In this lastregard, Gassendi’s views resemble those of his acquaintance,Hobbes, though with greater attention to core physical details of thematter theory, and fine-grained notions as to how the micro-mechanismsmay operate.

Gassendi reveals atomist sympathies in his earliest works andcorrespondence, where he rejects much of the style and some of thesubstance of philosophy in the late Aristotelian tradition. Indeed,some commentators see Gassendi as a thinker in the Renaissance moldwho simply lands on atomism as a central component of a broaderEpicurean alternative system to the robust range of receivedAristotelian views. However, though he shares most of Epicurus’sclaims about atoms (and many Epicurean arguments for those claims),Gassendi disagrees on key points. This suggests it is the merits ofthe view itself, that it is the most likely physical hypothesis aboutthe underlying structure of matter, and not simply a generalrestoration of Epicureanism, that leads him to atomism.

The broadest atomist claims Gassendi makes are rooted in hisbackground metaphysics and rejection of the infinite divisibility ofmatter. He grounds the finer points of his atomism—regarding thequalities of atoms and their aggregates—on observations,experiment, and interpretations of the same, as well as hisassessments of alternative perspectives on matter theory. Followingthe Epicurean model (with debts to Lucretius, Democritus, and othersstill), he starts with a basic ontology of matter and void, anddevelops a thoroughgoing account of the physical world rooted in apicture of the inherent features of atoms. The general range ofphenomena and entities for which Gassendi offers atomist accounts owesmuch to the ancients. Many of the particular explananda do not,though, and a significant number of his explanatory arguments are hisown, at least in part.

Gassendi introduces notions of absolute space and time according towhich the universe is that which contains material Creation. In thecolloquial language of metaphysics, he lays out the ‘floorplan’ of his picture of the universe in which he understands Godto place the ‘furniture’, namely, atoms and theiramalgams. Space, time, accident, and substance are the basic and real(non-ideal) categories of existence: space and time are not modes ofsubstance (see section ten). ‘Matter’ refers to substancethat exists in space and time. Indeed, it is the sole and unchangingstuff of physical things and so must exist as long as physical thingsexist. Gassendi wants bits of matter to have their distinctivequalities without the scholastic imposition of form. In particular, heproposes, matter has essential and accidental qualities, though we canonly know the accidental ones, through experience.

As for the containing space in which atoms reside, Gassendi offersempirical and apriori arguments on behalf of a void. He takes thebarometric experiments of his day, including his own at Toulon, todemonstrate the existence of at least a partial, disseminated void.Moving beyond such empirical argument, he echoes ancientatomists’ reasoning. Thus he rehearses the classical argumentsthat without disseminated void between the parts of bodies, one cannotexplain division and separation of matter at the level of basicparticles, and that without theinane coacervatum, one cannotexplain the motion of bodies through space.

Both atoms and the void are for Gassendi‘principles’—by which he apparently means‘primary element’, following a Scholastic tradition. Itdoes not follow from this, however, that they are both substantival inhis view. Whereas atoms are primary principles of material substance,voids are non-substantival principles of separation in which bodiesare located, and by which they are separated and have their particularsort of supra-atomic structure.

To establish that atoms are the primary principles or elements ofmatter, Gassendi draws deeply on the well of ancient atomist argument.This sort of ‘historical evidence’ or‘testimony’ tolerably counts as one manner of support forphysical claims at the dawn of the early modern period. GivenGassendi’s pronounced empiricism, though, the degree of hisreliance on such testimony is surprising. He strikes an even moresurprising anti-empiricist chord in the introductory chapter of hisPhysics (Physicae Prooemium), pondering a stipulative accountof the natural world that consists of the right physical postulates.In the end, though, this approach is unacceptable for Gassendi, assuch a stipulative physics raises more questions than it answers. Hisalternative tack is a series of reasoned defenses of basic atomisttenets—frequently, amplifications and restatements of Epicureanand Lucretian arguments—including claims as to the existence andstatus of atoms as the primary material principles.

To take one example, Gassendi assumes material objects must havesome substratum composed of basic and indivisible elements(‘principles’), and proposes that atoms, as thebest candidates for the role of substrata, are the materialprinciples in question. To arrive at this first assumption, he followsEpicurus and Lucretius in adopting the Parmenidean dicta that nothingcomes from nothing and (conversely) that all matter must come fromsomething. He further embraces the ancient view that those dictaentail a common substratum for all matter, as the composition andresolution of material things always yield matter. To establish thatatoms are the best candidates for serving as this common substratum,he reasons thatwhatever would serve as matter’ssubstratum cannot pass from existence. Moreover, elements of suchsubstratum would be incapable of passing from existence only if theywere indivisible and thus had no void—that is, were solid. Yetthis common substratum cannot be featureless, formless primary matter,as the Aristotelians propose. It should havesomeidentifiable and unchanging features because such features areineliminable from matter. He concludes that all material objects mustbe composed of elemental particles sharing the features essential tomatter—and the particles with those features just are atoms.

In a second line of Lucretian reasoning, Gassendi argues that atomsare the primary principles of matter on the grounds that somefundamental material elements must be impenetrable if we are toaccount for varying degrees of resistance in macro-sized objects. Hesuggests that since all material things resist pressure to someextent, they all have one or another degree of solidity. The only wayto explain this range of solidity, or resistance to pressure, heclaims, is by supposing that the ultimate constituent elements of allbodies are not soft, which is guaranteed if they are all solid.Otherwise, there could be no bodies harder than the softest ones, forif the ultimate constituent elementswere soft, then moresolid bodies could never be composed from them. From this he concludesthat all material things must be composed of maximally hard elementswhich, when put together with more empty space between them, yieldsofter bodies—and, when put together with less empty spacebetween them, yield harder bodies.

As in the previous line of reasoning, Gassendi seeks to establish thatsome properties of macro-sized objects—variable solidity here,immutable materiality in his first argument—require anunderlying atomic architecture. Unfortunately, the atomic accountoffered by the present argument also is not necessary to explainingthe macro-property—for we can still have diverse degrees ofresistance to pressure even if the basic elements of matter also rangein degrees of solidity. Worse still, this account is not evensufficient to the task. Given that atomic size and the amount ofinterparticulate void are also variable factors, differentcombinations of these structural characteristics could yield identicaldegrees of solidity across the otherwise very distinctive macro-levelobjects they compose. Then varying atomic architectures is notsufficient for varying degrees of resistance to pressure in objects onthe macro scale.

Such arguments and objections aside, Gassendi focuses his greatestefforts to deny matter’s infinite divisibility on the relevanceof mathematical and geometrical considerations to physical accounts ofmatter’s ultimate or near-ultimate particles. Whileacknowledging the broad conceptual parallel between physical andmathematical continua in ancient discussions (O I 262b), he warnsagainst the mistaken notion that physical magnitudes should beinfinitely divisible just because mathematical magnitudes are (O I263b). This last observation by itself fails to establish that atomsare actually divisible. Yet Gassendi views this notion as the collapseof a major argument against atomism. More generally, though, he isless swayed by any particular arguments for or against atomism than heis by the merits and value of taking atomism as a best workinghypothesis, with which we may explain a wide variety of sharedproperties among macro-sized objects—as well as those propertiesthat differentiate them.

A more fundamental task is the enumeration of atomic properties.Gassendi distinguishes between two sorts: those properties inherent inand essential to all individual atoms, and those which are a featureof atoms in groups. His list of inherent atomic features, whichclosely follows Epicurus’s list, includes: extension, size(moles, or more recognizably,magnitudo), shape(figura), weight or mass (pondus), and solidity(soliditas). Relative to each of these features all atomsgenerally resemble one another, there being a limited range of sizesand weights. One exception is shape. In order to account fortremendous variety among natural objects, Gassendi claims, there mustbe very many different types of atomic shapes (though not infinitelyso), and many tokens of each type (again, not infinitely so).

Another notable feature of this list of properties is that it signalsGassendi’s rejection of the cartesian view that extension issufficient to characterize what is essential to the least bit ofmatter. Descartes is wrong, then, for the same reason that theScholastics are wrong to talk about featureless matter in the contextof physical theory. As Gassendi argues, while we might abstractlyconceive of matter with one feature such as extension (or none at all,per the Scholastics), matter cannot actually come into existencewithout the features that God assigns at Creation—namely, size,shape, weight, and solidity.

The essential feature of atoms which does the most work inGassendi’s physics—and also generates the mostdifficulties—is their inherent weight, which gives them anintrinsic, naturaltendency to move. Given this tendency,atomic rest is either provisionary or else an illusion. Atomic weightgives rise not only to a simple capacity for constant motion, but alsoto a range of more complex behaviors, enabling atoms to“…disentangle themselves, to free themselves, to leapaway [prosiliendi, to spring out], to knock against otheratoms, to turn them away [retundendi, to check], to move awayfrom them, and similarly [they have] the capacity to take hold of eachother, to attach themselves to each other, to join together, to bindeach other fast…” Three other facets of atomic motionmerit our attention. First, it must be the general tendency of atomsto move in straight lines given that the atoms here do not feature theclinamen, or swerve (contrary to the Epicurean tradition,though perhaps as Epicurus himself would say). Second, Gassendiproposes that God endows atoms with a robust set of capacities formoving themselves to varying degrees—leading some commentatorsto see Gassendi as a vitalist or animist. Finally, Gassendi subscribesto a seamless compositionality of matter and scalar invarianceregarding the nature and laws of motion, each of which lead him intomurky waters. On the micro-level, he is committed to a constancy ofmotion that cannot be permanently arrested, whereas on themacro-level, he holds that a principle of inertia governs the motionand rest of all bodies.

Gassendi’s compositionality thesis consists of the claim thatthe varied combinations of atoms give rise to all manner of physical,chemical, and biological features of the world and the phenomena theyexhibit. Two elements of this thesis are noteworthy. First, atomscombine into particular molecular structures that correspond toparticular macro-level features and phenomena. This pre-Daltonian viewoffers no suggestion that diverse collections of atoms are the sourceof molecular variety. Yet this molecularism is novel all the same forthe broad suggestion that such micro-structures are intermediate-levelbuilding blocks of macro-structures, and for the particular proposalthat the four Aristotelian basic elements be conceived of as molecularaggregates. Second, molecular structuresen gros behave inthe same ways as macro-level structures: they can be set in motion,pulled, elongated, compressed, and so on. In the case of molecularcrystal structures, they can replicate, much as their macro-levelcounterparts can. On the other hand, there are significantdissimilarities among atoms and molecules: motion, density, andelasticity are all points of difference, which suggest the difficultyof a unified and internally consistent matter theory, relative tophysical norms or laws. Yet Gassendi is confident that, at least inprinciple, the universe could have been created by God with any givencomposition of particles, as varying in size, shape, or any otherdimension. This suggests that from that level of abstraction the lawsgoverning motion (not contingencies for Gassendi) are intended to bescalar invariant. Even in cursory review, these tantalizing claimssuggest significant and controversial consequences of stipulating thatatoms have inherent weight and resulting tendencies to motion.

A further hallmark of Gassendi’s atomic and molecular theoriesis his suggestion, following the views of early atomists (prominentlyLucretius), that some atoms are endowed with greater activity thanothers. The varied activity of such special atoms, orseminarerum, gives rise to a differential dynamism in matter (of purelymaterialist nature), allowing for special organic structures, as wellas growth of crystals. By contrast, neither atoms nor molecules areendowed with powersper se. Nor do atoms bear forces, thoughcertain forces such as gravity can be explained by reference to thebehavior of atoms. Chemical forces, on the other hand, have molecularexplanations.

One of the greatest challenges to Gassendi’s atomism from aninternal perspective is the seemingly quixotic nature of his searchfor empirical foundations for atomism. In his era there is not thebarest hint of perceptually-derived knowledge of anything so small.There is, he thinks, an empirically viable source of at least someclaims concerning atoms—the indirect data of indicative signs.Yet the general tenor of his characterization and defense of physicalatomism signals a departure from his customary empiricism. As in hisdefense of an indivisibility thesis, Gassendi relies foremost onreason, not experience, to account for the origin and quantity ofatoms and what he takes to be their essential and inessentialproperties, their internal impetus, motion, and causal role, and theircontribution to the motions and qualities we attribute tomacrophysical objects. He is hardly to be faulted in this regard giventhe lack of direct empirical evidence available. Moreover, hisresponses to ancient and early modern critics of atomism are firmlywithintheir strategic bounds, as they typically rely onreasoned argument without appeal to empirical force.

6. Atomist Natural Philosophy

For Gassendi, the great promise of the atomist hypothesis is theexplanatory power across diverse domains of material phenomena (andthe great test, where feasible, is the gathering of empirical evidenceon behalf of that hypothesis). Gassendi’s advance here is todevelop atomist accounts that are mechanically viable, where nonepreviously existed—whether because prior mechanical approacheswere thought inapplicable or because no solutions as such approachesyielded were actually successful.

In what we today think of as chemistry and physics, Gassendi developsa great range of applications for his atomist hypothesis. In hisoptics, the atomist theory of light provides a counter toDescartes’s view of light as pressure. For Gassendi, light is aproperty carried by particular atoms (atomi lucificae) thatare identical with heat atoms. These tend to travel at greater thanaverage velocity because they generally have fewer obstacles in theirpaths than most atoms (O I 422a-432b). Sound, too, is particulate, andtravels as such particles travel. In contrast to a typical sound-waveview, the surrounding medium does not play an important role: Gassenditakes the velocity of sound particles, like that of light particles,to be invariant with respect to the air or wind in which they travel.In an experiment he models after a similar one of Mersenne’s, hejudges the velocity of sound to be 1,473 ft/sec [478 meters/sec] (hiscalculations are off by 435 ft/sec [146.7 meters/sec]) and invariantto the pitch of the sound (O I 418a-419a). Even planetary motion hasan ultimately atomist explanation, as the underlying forces drivingthe planets are magnetic forces borne by dedicated atoms (this is anatomist modification of a view developed, though later abandoned, byKepler).

Gassendi’s atomist accounts of chemical phenomena are equallyambitious, suggesting among other things how vapors are created andmetals are soluble. Vapors are brought about by increases in thedistance between atoms in a liquid volume. Heat atoms remove some ofthe atoms present in the volume, resulting in a greater percentage ofvoid and the matter taking the form of vapors (O I 398b-399a). Asconcerns solubility, we account foraqua regia dissolvinggold, andaqua fortis dissolving silver, as a result of theircomplementary atomic structures: gold atoms fit the pores ofaquaregia and silver atoms fit the pores ofaqua fortis (OII 33b ff, 39a-b).

In the realm of biological phenomena, Gassendi offers greatly diverseaccounts drawing on an atomist framework. His most significantproposal in this regard is an account of generation and inheritance interms of a material ‘soul’ oranimula bearingontogenetic information. In sexual reproduction, two sets of seminalmatter and corresponding animulae meet and jointly determine thedivision, differentiation, and development of matter in the neworganism. The determination of inherited traits requires combining orchoosing among each parent’s contributions, entailingcompetition and dominance among the animulae (O II 284b-285a). Theanimula is defined in terms of its constituent atoms, which must beuniform in order that animulae may operate equivalently acrossdifferent modes of generation, whether ‘pre-organized’ orspontaneous. Further, Gassendi offers his molecular model as amaterial means of storing ontogenetic information received from thesouls of parent organisms (O II 170b-171a, 280b).

Rather more curious stories are found in his accounts of development,physiology, and behavioral psychology. Thus, the root cause ofincreased shellfish growth and marrow production during full moons isincreased humidity, stemming from the excitement of lunar moisturecorpuscles by sunlight. These corpuscles are then transported to theEarth by rays from the sun reflected off the moon (O I 450a-451a). Heaccounts for toxicological phenomena, such as the stunning capacity ofelectric rays (torpedine), as emission of corpuscles with adulling power (O I 454b-455a). Other poisons provoke strange behavior,such as those of the tarantula. These may work by producing activityin the victim sympathetic to the attacker’s activity, a resultof chemical alterations the poisons bring about in the victim’ssensory capacities and attunements (O I 456a). As concerns animalpsychology, Gassendi endorses Lucretius’s suggestion (RN IV)that lions avoid roosters at dawn because the latter can injectharmful corpuscles into the former’s eyes (O I 453b-454a). Sheepavoid unfamiliar wolves because wolves emit corpuscles of an odoroffensive to sheep (O I 456a).

As concerns human psychology, Gassendi offers a materialist (henceultimately atomist) account of the passions as a function of thevegetative soul, including desire and fear, and motivating pleasureand pain (O II 474f, 495f); these are ultimately governed, however, bythe rational and immaterial soul. There are, broadly, any number ofcognitive faculties and attributes that may be built out of or beproduced by atoms, Gassendi suggests, countering Lactantius’scomplaint that the ‘senses, thought, memory, the mind, genius,[or] reason’ cannot so be constructed. As with the passions,though, there are limits. A viable atomist story can be told ofsensory phenomena and idea-formation though not reason and its alliedphenomena (O I 282b). Yet there is clearly some grey area, as memoryin particular seems open to a purely materialist account. Memory lossresults from a physical change in the brain resulting fromundernourishment; folds in brain matter preserve the physicalembodiment of memory, but a deficiency in nutrition leads to thedeterioration of those folds (O II 406b-407b; a similar Cartesian viewappears in theTreatise on Man (AT XI 177–178)).

7. Materialism, Libertinism, and Ethics

The thoroughgoing nature of Gassendi’s atomism has led numerouscommentators from Descartes to Marx to view him as taking all worldlystructures and behaviors to be explicable by the interaction ofmaterial bodies. According to this picture, Gassendi leaves little ifany room for the existence of non-material substance or its relevanceto metaphysical or natural accounts. One piece of putative evidencefor materialism in Gassendi’s corpus is his extension of atomistexplanation, from all physical phenomena to a large range ofnon-physical phenomena, including aspects of the mental, social, andethical. This is not entirely compelling, as we have seen that thematerial underpinnings of our mental apparatuses is relevant to onlysome portion of his psychology.

A second piece of suggestive evidence for Gassendi’s materialismis historiographical and rhetorical in character. Epicurus andLucretius were the great ancient materialists, Gassendi is their greatearly modern exponent, hence Gassendi too was a materialist—hisChurch-oriented misgivings notwithstanding. This thesis requiresthinking of Gassendi as holding closeted views relative to the Churchand Holy Writ, and indeed many of his views are highly nuanced in thisregard (q.v. his stance on Galileo). It is not clear, however, thatGassendi intends anything other than a carefully delimited set ofaccounts of materialist ilk, within what he considers to be the properrealm of the physical. Strictly speaking, though, materialism is not adoctrine by degrees, and that Gassendi’s proposed realm of thematerial extends beyond the reach of other, competing views of histime does not make him a materialist in the pure sense.

A third piece of suggestive evidence was Gassendi’s membershipin the group known as thelibertinsérudits.Other members of this diverse group, on a broad construal, includedGuy Patin, Pierre Charron, François Le Vayer La Mothe, GabrielNaudé, Théophile de Viau, and Cyrano de Bergerac.Molière is also sometimes considered to have belonged to thelibertins, and he is thought to have studied underGassendi’s informal tutelage (Sortais 1922). Gassendi’sties to thelibertins also brought him in contact with arange of other intellectuals and artists—the latter including,most notably, Nicolas Poussin. Thelibertins, constitutingmore of a literary salon than the philosophically- andscientifically-oriented Mersenne circle, promoted a moralitydetermined by reason, stripped of theological considerations, anddefined on an individualist basis. In their commitment to intellectualliberty, they professed a diverse mix of metaphysical and epistemicviews, especially materialism, skepticism, rationalism, deism, andEpicureanism—each party to the group offering a different mix.They were politically and socially savvy enough to promote theirlibertine views in a manner and style that verges on the secretive.Such secrecy as a guiding stylistic force can be seen in aspects ofGassendi’s writing and rhetorical style, as he frequently makesallusions likely to be understood only by his friends or the equallyerudite, constantly draws on expressions from ancient sources to makehis own points, and offers a variety of quasi-coded rhetoricalelements, most famously including his somewhat hesitant and qualifiedendorsement of the Copernican model.

Owing to their largely individualist conception of ethics—and inkeeping with late Renaissance tradition, thelibertins tendedto avoid political theory and larger social issues, focusing insteadon self-governance and morality understood in terms of character.Gassendi generally follows this conception in his ethics (Sarasohn1996), though he also outlines a broader political theory (Paganini,1989–1990). Aside from elements of his ethics and rhetoric, itis an open question as to how much effect Gassendi’s associationwith thelibertins had on his views—or for that matter,how much influence he may have had on them. In one area inparticular—obeisance to the Church and its teachings—hediverges significantly from hislibertin counterparts.Gassendi routinely emphasizes the sacred nature of Holy Writ and thenecessity (as well as benefits) of amending Epicurean thought to meetstrictures of accepted dogma. This adherence suggests thatGassendi’s interests in personal responsibility, empiricalinvestigation, and the underlying nature of matter did not signal aconsummate atheistic humanism, denial of spiritual activity, ormaterialism. If anything, one might suppose that his innovativeethics, scientific method, and physics were artificially constrainedby his canonical beliefs. A more accurate reading is that he trod aline between Church orthodoxies and the most radical alternativesassociated with the mechanical philosophy and early modern ethics,such as we find in Hobbes. Gassendi was a moderate modern thinker,promoting the new against a background of opposition the potential ofwhich he knew quite well.

Though we lack grounds for calling Gassendi a complete materialistmoralist, a broad look at his ethics may suggest strong links to hisphysics, in a Hobbesian manner (Sarasohn 1996). This parallel shouldnot be taken too far: Gassendi and Hobbes diverge in their views ofhuman agency and disagree about our unfettered, non-physicallydetermined capacity for moral deliberation. However, they each acceptthat pleasure in some way motivates moral choice (though Gassendi alsomakes allowance for the role of irrational appetite).

Indeed, insofar as Gassendi considers pleasure to be amaterially-realized phenomenon, he shares Hobbes’s view of themorally correct as something that can be defined in physical terms.However, according to Gassendi and the lessons he draws from hisEpicurean and Stoic sources, any spirtually-related pleasure trumpsany materially-related one (O II 710a-b). The truestpleasures—hence goods—are defined along the lines ofEpicureanataraxia (attainment of tranquility) and Christianvirtues, including in particular love of God, and friendship and goodwill among persons. The guarantee of our ability to seek tranquilityor fulfill these virtues is our free intellectual judgment(libertas). Such a freedom consists in the ability of ourintellects to choose between good and evil, and this is turn yieldsour capacity for volition, or free will (O II 821b-822b).

Free will and the ability to exercise conscience are also key conceptsunderlying Gassendi’s views on society and the body politic.Gassendi agrees with Hobbes (and shares a Lucretian inspiration(Sarasohn 1996)) that individuals in a pre-social setting aremotivated by fear and desire for betterment, which leads them to joinin a commonwealth and concede at least some rights. For Hobbes, thismotivation is driven mechanically, and the commonwealth entailsforegoing individual rights in return for security. For Gassendi, onthe other hand, the motivation is driven by irreducible reasonedconsideration, in favor of the stability of social convention.Further, this social contract leaves intact at least those freedomsand liberties which, to begin with, figured in rational choice of thecontract over the state of individual insecurity. Gassendi veers froma strict physicalism, proposing that societies are organized by socialagreements chosen through operations of the immaterialanimus(O II 795a).

8. Space and Time

Even putting aside the framework of atoms and void, the Gassendistontology poses an alternative to rival Aristotelian and Cartesianviews, with respect to space and time. Gassendi’s conception oftime and space is absolute. Time flows uniformly irrespective of anymotion, and space is uniformly extended regardless of any objects thatmay be contained within it (O I 183, 285). Indeed, both space and timepre-date Creation, and are infinite in character.

Gassendi borrows heavily on themes set out by earlier Italian spaceand time theorists, including Campanella, Bruno, Telesio, and Patrizi.One possible advance is suggested by his discussion of such anontology as a prelude to his matter theory: space and time arepre-conditions for the existence of substance, rather than propertiesof substances (as the Aristotelians would have it). In this regard,Rochot (1971) proposes that Gassendi’s ontology provides atomsas stable entities and absolute space-time as a stable environment,which together allow for a greater reliability of empirical data hencea greater reliability of our data reception. The notion is that thosedata have some fixity at the source, at least, given that thespace-time environment that contains material elements giving rise tosuch data are unbended by relativistic position to anything else.Naturally, such fixity would be only a necessary condition, and evenfails to provide guarantees at the level of basic sensory data, whichGassendi recognizes in his discussion of the Skepticist tropes.

Gassendi’s notion of non-relative space stands in directcontrast to the Cartesian plenist account, which suggests that spacejust is place, as defined by the extension of the resident (anduniversal) matter. This contrast bears a clear result relative tomatter theory: Descartes is locked into a view of matter as infinitelydivisible, in order to account for the absence of void or, whatamounts to the same thing, the omnipresence of matter. Gassendi, onthe other hand, is free to pose the existence of atoms and the void,where matter is located in space but is neither defined by nordefinitive of that space.

9. Logic

Broadly speaking, Gassendi expresses some three notions of logic intheSyntagma. The first, enunciated in the history of logicsection that appears immediately prior to theInstitutioLogica, suggests a picture of logic along heuristic and didacticlines, in the manner of Ramus, whose theory Gassendi lauds as a guideto organizing and presenting existing knowledge (O I 59a-62b). Thesecond suggests that logic consists in the Aristotelian syllogistic,the understanding thereof, and related methodological concerns. Thethird suggests that logic consists in the study and use of causalreasoning, and related methodological concerns—most notablyincluding an exposition ofregressus demonstrativa theory inthe manner of Zabarella and Nifo (this notion expressly contradictshisExercitationes view that such causal reasoning cannot bejustified). These latter two notions yield the main thrust of theInstitutio (though the discussion of demonstration in Book IVhas clear Ramist debts). They also have great currency for Gassendi,who typically crafts his use of syllogism and causal inference andmethod after hisInstitutio conceptions, or at least signalsthat he intends to do so. The same may not be said for his Ramistconception. For although he makes ample use of rhetoric, he does notturn to definition, distribution, or division for the purposes ofdiagramming or expounding existing knowledge—per the logic ofRamus—in any way that matches his interest in the traditionallyAristotelian conception of analysis as problem-solving.

It has been suggested that a fourth notion—a psychologisticaccount of cognitive operations, and perception in particular—isa prominent goal of Gassendi’s logic (Michael, 1997). While suchdiscussion forms part of theInstitutio presentation, it isby no means the main goal of the work or of Gassendi’sconception of logic. This can be seen from the thrust and length ofhis discussion of the first three elements, and in particularsyllogistic and causal reasoning, and their attendantmethodologies.

10. The Scientific Endeavor: Astronomy, Optics, and Mechanics

Gassendi’s science is philosophically noteworthy in the way thatDescartes’ or Kepler’s science is, drawing on a robust setof views on the nature of the world and what we know of it. Hisscientific work in astronomy, optics, and mechanics is of particularimport in suggesting how we should pursue a purely empirical pictureof the world, within the limitations of our sensory access and theconstraints of tradition.

The principal elements of Gassendi’s astronomy include a globalembrace of empirical method, advanced instrumentation, andmeasurement, an interest in unusual celestial phenomena, and apartially masked defense of Copernicanism. His embrace of anempiricist astronomy can be gauged by his voluminous recordedobservations—some presumably with the telescope lenses sent byhis friend Galileo—carried out in concert with a league offellow observers strung across Europe and the Near East. A primarygoal of these recorded observations was to confirm and extend theRudolphine Tables, the project set up by Tycho Brahe and completed byKepler, to facilitate calculation of the planet’s positions(which goal in itself suggests Gassendi’s adherence to aKeplerian heliocentrism). Another facet of Gassendi’s empiricistastronomy was his denunciation of astrology as crafted independent ofany ideas from the senses, impervious to correction by experiment orobservation, and thus as failing to qualify as natural or experientialknowledge. This view brought him into direct and bitter conflict withJean-Baptiste Morin, who also suspected Gassendi of anarch-Copernicanism that was not only against Church teaching but wouldobviate the astrological structures central to Morin’s theories.Gassendi’s close interests in observation also led to employingthecamera obscura to gauge variations in the apparentdiameter of the moon—in accordance with its orbit of the Earthand the apparent diameter of the Sun. Further, in his work withPeiresc, Gassendi tackled the problem of determining longitude byreference to lunar eclipses, later working towards this goal withClaude Mellan on the first effort to chart the moon.

Gassendi’s interests in unusual celestial phenomena dates backas early as 1621, when he observed the colorful illumination of thesky and dubbed these lights ‘aurora borealis’. Based onhis correspondence with observers as far away as the Levant, helocated the source of the illumination at very high altitude, abovethe Northern Polar region. In 1629, he observed the rare phenomenon ofparhelia, or false suns, which he explained in his Parheliaseu soles…, in terms of the reflection of sunlight by ice orsnow crystals at high altitude. This account, shown to be accurate inthe nineteenth century, relies on the views of Gassendi andPeiresc—based on their microscopical observations—thatcrystal formations of snow and ice are highly reflective. The greattriumph of Gassendi’s scanning of the skies was his observationof Mercury’s transit before the Sun (1631), the first suchrecorded observation and a confirmation of Kepler’s predictionof the planetary orbits in accordance with the Three Laws. Thisconfirmation in turn enabled the subsequent calculations (Halley andGallet, 1677) of the distance between the Earth, the Sun, and theother planets.

The most controversial element of Gassendi’s astronomy concernswhether, and to what extent, he may be counted as a defender ofGalileo and the Copernican view. There is little question that hesympathized with Galileo, and that he was fully aware of the merits ofCopernicanism, at times defending the view and some of its main planksopenly. Yet he was also clearly concerned with allegiance to Holy Writas interpreted by the Church, and to this end offers a Church-friendlyaccount of the condemnation that focuses not on the underlyingheliocentrism but on particularities of the Galilean model (O V 60b).His considered judgment is that the Tychean model is preferable to thePtolemaic model, but also to the Copernican model—in the lattercase simply because the heliocentric picture does not fit with Churchteachings. He hastens to suggest, however, that those teachings arethemselves warranted by our own current empirical evidence—theimplication being that such truths and the concomitant rejection ofCopernicanism might well be revisable.

Closely related to Gassendi’s interests in astronomy are anumber of issues in optics, where he sought to articulate aphysiological model of vision and a physical model of light. In sodoing, Gassendi contributed to early modern efforts that wouldeventuate in distinguishing these two ends of traditional optics.

His integrated optics model follows an Epicurean and Lucretianintromission view, that vision is a function of rays of light atoms orimage-bearing atoms that are received by our internal apparatus forvision. The structure of this apparatus was of great concern toGassendi and his early collaborator on naturalist projects, Peiresc.The premise of their work was that Kepler was largely correct inpostulating an optical image that gathers many rays into a coherentrepresentation in the eye, focused on the retina by the crystallinelens. What troubled Gassendi and Peiresc, however, was the notion thatsuch an image as cast upon the retina would be inverted, leaving theproblem of identifying how we see the world as right-side up. Seekinga physiological solution—as against any psychological capacitythat rights the inverted image—they suggested that the retinaitself acts as a mirror which rights the inverted image projected uponit.

Another aspect of this integrated approach to optics was a reliance oninternal perceptual phenomena to account for external phenomenaregarding appearances, illusory or otherwise. This was not auniversally-held view, even in the age of the optics of light andvision. In addition to Gassendi’s interest in parhelia, he alsosought to explain apparent discrepancies in the size of the sun andmoon at different hours by reference to visual experience produced bylight phenomena (De apparente magnitudine…, 1642).Thus, these bodies appear larger on the horizon than at their apogeebecause the pupil dilates from the differential exposure to the lightat the horizon. (In fact, all such apparent differences are producedby the distance effect of surface features of the area from which thecelestial body is viewed.) One key driver of such an appeal to theinteraction of light behavior and our visual apparatuses isGassendi’s view that some explanatory role must be played hereby the common atomic structure underlying the images intromitted intoour eyes and the light rays cast by celestial bodies which areunderstood as creating such images.

Gassendi’s mechanics shows the strong influence of the Galileanprogramme. He addresses the law of free-fall twice, first in a faultytreatment inDe Motu (1642), and next in corrected fashion inDe proportione qua gravia decidentia accelerantur (1646). Inthe earlier work, Gassendi focuses on forces compelling the fallingbody, which he takes to comprise the attractive force of magnetism andthe propelling force of air behind the falling body. This combinationof forces, he suggests, allows for the Galilean law that the distancetraveled by bodies in free-fall is proportional to the time of fallsquared. However, Gassendi mistakenly takes increases in velocity andin distances to be equivalent, leading him to manufacture a false needfor greater velocity attained than what would be produced by theattractive forces alone. InDe Proportione, he acknowledgesthis error, amends his calculations, and retreats to a causal accountthat rests on the single force of the terrestrial magnetic attraction.This is not one of Gassendi’s empirical triumphs,though—in neither work does he make any specific reference toobservations or experiments.

One notable success in the experimental domain is his performance ofthe Galilean test of dropping a stone from the mast of a moving ship,recorded inDe Motu. Once dropped, Gassendi shows, the stoneconserves its horizontal speed (equal to that of the ship, beforebeing released) and its motion describes a parabola given its downwardfall. This result successfully refutes one simple anti-Copernicanargument, by showing that the Earth can move without superaddingmotion to terrestrial objects otherwise in motion (whichsuperaddition, opponents of Copernicanism correctly maintained, wouldgenerate much havoc in the motion of terrestrial objects). This muchGalileo surmised in his original thought experiment, though theperformance was excellent publicity for the Galilean perspective andan opportunity for Gassendi to think through the issues at stake.

In this regard, Gassendi was able to take a step beyondGalileo’s conclusions, drawing from this test a generalizedprinciple of inertia (the Galilean version of inertia wasfundamentally circular, given that bodies in motion would trace theearth’s curve). Gassendi saw that the motion of the droppedstone at a sustained speed—in the absence of any contrary forceor obstacle—is an instance of inertial motion, albeit one wherethe motion is compositional (describing the parabola). Indeed, neithercompositionality nor directionality had any impact on inertial motion,Gassendi concluded: any body set in motion in any direction continues,unless impeded, in rectilinear path.

Other accomplishments in physics included a compelling measurement ofthe speed of sound (showing that sound travels at the same speed, nomatter the nature of its pitch), and the first satisfactoryinterpretation of the Pascalian barometry experiment. In his accountof the Puy-de-Dôme experiment, Gassendi proposes that variationsin air pressure are relative to atmospheric conditions and altitude,as the air is an elastic gas. He also suggests that this experiment(which he repeats at Toulon in 1650) shows that created vacuum ispossible, at least as accumulated among part of the air particles inthe instrument ‘sealed’ by the mercury column in theexperimental apparatus. In establishing the elasticity of air as a gasand accumulated void as a result of particle displacement, Gassendievokes his ontology of atoms and the void.

11. Impact and Influence

Gassendi’s views were often transmitted in the early modern erathrough the medium of François Bernier’sAbrégé (1678/84), which work highlights theatomist views and materialist tendencies of Gassendism. Such themes,as well as empiricist threads of Gassendism, were attractive to anumber of late seventeenth century physicists and physicians (viz.Nicholas de Blégny, Guy Patin, Antoine Menjot, and GuillaumeLamy) and other philosophers (viz. Gilles de Launay), as well as thoseamong the Montmor circle orlibertins érudits (viz.Samuel Sorbière, Jean Chapelain, and Cyrano de Bergerac). Stillothers, especially Cartesians such as Desgabets and Cordemoy, wererather distasteful of those themes, as were hard-line theologians suchas Louis Le Valois.

As Lennon (1993), Brockliss (1997), and others have noted,Gassendi’s overall influence in the French education system wasnot a match for the Cartesian alternatives, and his views wereconsidered especially unworthy after his atomist views gained currencyin England.

The British success of Gassendism had three textual sources. Inaddition to theOpera Omnia and Bernier’sAbrégé, Walter Charleton produced a selectiveand amended English translation of parts of the Animadversiones,intermingled with other sources and his own perspectives (1654). Therewas as well a group of atomist enthusiasts in the Newcastle Circle,and a small existing British Epicurean club, whose members includedKenelm Digby and Nathaniel Highmore. This backdrop of sympatheticsources, not entirely faithful to the original, allowed a substantialand diffuse influence of Gassendi’s views in British thought. Wesee Gassendism shaping the work of lesser figures such as FrancisGlisson (who embraced avis motrix) and Thomas Willis (whocrafted a materialist theory of neural transmission based onGassendi’s view (Wallace 2003)) but also such major thinkers asBoyle, Locke, Newton, Hume, and Reid. Those sources of influencethemselves were sufficiently diffuse that it is difficult to makeprecise Gassendi’s imprint on these later authors, except wherethey explicitly acknowledge their debts.

Boyle finds Gassendi’s thinking agreeable in three respects.First, he embraces Gassendi’s criticism of Descartes’ontological argument as rooted in an assumption as to the nature ofGod impervious to proof. Second, he follows in the Gassendist model ofplacing empiricism and experiment at the center of a viable scientificmethod. Third, he praises Gassendi’s corpuscularian theory as aworthy ontology for the mechanical model of explanation, hastening toadd that further experimentation should give sufficient demonstrationof the verity of atomism. Indeed, he refuses to judge between theGassendist and Cartesian alternatives, presumably on the grounds thatwe cannot produce evidence to decide the issue of matter’sinfinite divisibility.

As Locke is concerned, it is by now well established that he may haveread Gassendi directly, and almost certainly read Bernier. Theevidence of influence shows up in some central Lockean theses: thecorpuscularian philosophy (here he follows Boyle as surely as he doesGassendi), primary and secondary qualities distinction (a view alsoheld by Boyle, Descartes, Galileo, and others still), and broadcommitment to empiricism, including the negative thesis against innateideas and the positive thesis identifying sensory data as the primarysource of ideas. We also see Gassendi’s likely inspiration inLocke’s probabilist embrace of an understanding of naturalphilosophy through less-than-certain claims about the world, thoughhis sub-par ranking of ‘sensitive apprehension’ of theworld is a rejection of the Gassendist picture of sensory knowledge asthe best for which we might hope. Locke’s theory of language,too, reveals Gassendi’s influence: the notion of nominalessences resonates with the proposal in the Institutio Logica that themeaning of general terms is a function of our sensory-based ideas,which contribute to our picture of the properties we typicallyassociate with the objects of those terms. Finally, in regard toethics, Locke offers a perfectly Gassendist linkage between good andevil on the one hand and pleasure and pain on the other, and likeGassendi celebrates the notion of personal autonomy, though he locatesthe seat of moral judgment in external norms (most prominently, thenatural law) rather than any internal ideals or virtues such asGassendi upholds.

Newton reveals various interests in Gassendist themes, dating to anearly reading in his student days (see theTrinityNotebooks). For one, he adopts the notion that Aristoteliansubstance and accident fail to define all existents, and (along withBarrow, who likely read Gassendi as well) suggests that absolute spaceand time represent the fundamental ontological framework into whichmatter and its phenomena are located. For another, he espouses a formof the mechanical philosophy, albeit one that departs from orthodoxy(as pronounced by Gassendi) in that God plays a significant andsustained role in determining the course of natural phenomena. Here hefollows Gassendi’s thought most closely in admitting atoms tohis ontology, nearly replicating Gassendi’s list of atomicproperties, proposing that atomic structures yield chemical bonds thataccount for the structures of larger bodies, and endorsing theGassendist notion of light as flowing in a stream of atoms (inopposition to the Cartesian wave theory promoted by Hooke andHuygens). In the spirit of Boyle, though, Newton tends to treat hismatter theory as instrumentally useful rather than as a universalhypothesis in search of further instances. In this way he hopes toavoid the hard questions about our ability to summon empiricalverification of their existence or precise character. One famousNewtonian methodological dictum indicates there are aspects of atomswe can know, however. In thePrincipia (1687), Newtonsuggests a transdictive principle of Gassendist provenance (alsoembraced by Locke), according to which the basic properties of bodieson the micro-scale (“the least particles of all bodies”)may be inferred from such properties of bodies as we have evidence of,on the macro-scale.

Hume is less interested in affirming ontologies than in showing why wehave no good reason to invest belief in them, and accordingly picks upon the rather different Gassendist theme of coming to terms with theancient Skeptics. His moderate or constructive skepticism(pace Popkin) is founded on doubts concerning the possibilityof justified belief, focusing on the problem of induction as the greatdifficulty undercutting our ability to know about the world. Lackingrational justification, we simply fall back on induction as apracticable means of grasping and managing our experience of events.Here we see a striking similarity with Gassendi’sassessment—beginning with the observation that justifying anygeneralization on particulars requires something beyond our cognitivepowers, namely, our empirical knowledge of all such particulars. Fromthis point, Hume draws the Gassendist lesson that induction cannot bedemonstrative, for lack of this generalization step or the supposition“that apart from those enumerated there occurs none which isdifferent” (O I (Institutio Logica) 113a). Finally,Hume’s proposed resolution also resembles Gassendi’snotion that we might simply posit, as a matter of utility, theconformity of all remaining unenumerated particulars.

Into the late eighteenth century, we see Gassendi’s influence inReid’s theory of external knowledge. This theory is centered onthe notion of what he calls ‘suggestion’, or the evincingin us by our sensory data of concepts corresponding to the qualitiesof things in the world. In its broad sense, ‘suggestion’consists in a signing relationship—as a matter of convention,custom, or biology—between things or events in the world whichmay be construed as signs (in the case of conventional signs, thesemay be linguistic or symbolic entities) and what those things orevents signify. Here Reid draws on the long tradition of theories ofsigns, likely relying in this instance on Gassendi in particular,relative to the distinction between conventional(‘artificial’) and customary and biological(‘natural’).

Gassendi’s influence spread further still, beyond Britain or themodern era. The young Leibniz consciously followed Gassendi inembracing atomism, later retaining high regard for mechanism butabandoning the material model of substance in favor of the monadology(Moll 1982). Christiaan Huygens pursued numerous Gassendist themes,including anti-Aristotelianism, probabilism, a method of hypothesis,and atomist matter theory. Gassendi’s libertine, atomist,empiricist, and quasi-heliocentrist views also met with keen interestfurther afield, among like-minded philosophers and natural scientistsin early modern Poland, Italy, and Spain (Murr, 1997). In more recenttimes, Gassendi would come to be seen as anticipating such notableviews as Mill’s proposal that mathematical knowledge isempirical, and Popper’s notion that empirical falsifiability isa test of a hypothesis’prima facie viability.

12. Recent Commentary on Gassendi

The precise place of Gassendi in the history of early modernphilosophy and science is only partly articulated by recentscholarship, which has tended to focus on one aspect or another of histhought, and to portray Gassendi primarily as an opponent of one oranother contemporary, to the neglect of his positive theses. Thelaudable goal of such contextualist studies is to demonstrate his keyrole in important debates of the era, yet the picture that emergesfrom deliberation on these commentaries is rather Gassendi’srelative eclipse by other figures, notably Descartes. For example, onehistorical approach (Brundell, 1987) highlights a stronganti-Aristotelian strain which guides Gassendi’s earliercriticisms of the Scholastics as well as his later Epicurean works.From this perspective, Gassendi may be seen as fighting the samebattles as Descartes, and losing in any such comparison because heengages his foes with generally lesser flash and apparently lesssophisticated, or at least less novel, weaponry. Another commonapproach (Joy, 1987; Darmon, 1998; Mazauric, 1998; Taussig, 2001 and2003) is to emphasize historicist and rhetorical elements ofGassendi’s method, as employed in his conversations andcorrespondence with members of the Mersenne circle. Gassendi’srole in that context was by no means marginal, and it is impossible todownplay the centrality of that circle in early modern scientificdebate. Yet the most important figure to this group was not actuallyan active participant in it, and this was Descartes. Mersenne, ofcourse, is the other core personality in this context, and so Gassendiby default is at best a third. Gassendi perhaps fares worst incomparison with Descartes in recent discussions of their directconflict over theMeditations, where Gassendi’santi-Cartesian views are presented as a prism through which we maybest perceive the spectrum of his views (Osler 1994, Lennon 1993,Grene and Ariew 1995). There is undoubtedly a case to be made that herepresents the most prominent alternative to Descartes in his times.However, highlighting this story encourages the view that Gassendideserves no more than footnote status and emphasizes, at leasthistorically speaking, his role as thelosingalternative.

Another fashion has it that Gassendi’s doctrinal beliefs formthe foundation of, or otherwise influence, his philosophical andscientific views. One such perspective suggests that his spiritualconcerns and materialist ontology jointly shape the character of hismetaphysics—leading to irresolvable internal conflict (Bloch1971, Sortais 1922). Another perspective has it that his theologicalviews, and specifically his voluntarism, lead him to his empiricism(Osler 1994, Sarasohn 1996). But it is not clear that Gassendi is bestunderstood as laboring in service of a doctrinal credo, or asmotivating his philosophical views by appeal to his theologicalsensibility. He indeed tailors his Epicurean views to meet theologicalconstraints and endorses the only astronomical world-view he believesacceptable to the Church, that of Tycho Brahe. Yet Gassendi’sdefinitive criterion for any physical, metaphysical, orepistemological thesis is approximation to the truth, which isempirically-determined. On the other hand, some theologically inspiredclaims are woven into the fabric of his metaphysics and psychology.For example, there are two souls, one sensitive and the otherspiritual, and the latter is required in order to satisfy religiousdemands for an immortal unity attached to, but not susceptible to thefate of, the material body. But in such cases Gassendi is generallyclear about non-philosophical motives, introducing such corrections oradditions to his reasoned or empirically demonstrated views as arenecessary by the dictates of faith or Scripture. He frequently defendsthe primacy of Roman Catholicism and faith over natural reason (O I5a, O I 49a, O II 237a-b) yet easily distinguishes between objects ofscientific and theological investigation and reflection (O III (DeProportione) 636a). To suggest that he arrives at the core tenetsof his metaphysics or epistemology in order to draw out the ultimateconsequences of his theology thereby misconstrues his broadphilosophical motives as well as his particular reflective andinvestigative strategies.

By contrast, another element of recent scholarship highlightsGassendi’s philosophical motivations and strategies insensustrictu. In the years during and following the Second World War,Bernard Rochot began this trend by bringing to light numerouslesser-known texts as well as the manuscript background to Gassendistatomism. More recently, Fred and Emily Michael have called attentionto empiricist sources and features of Gassendi’s psychology andepistemology. Others offering assessments of Gassendi’s views insimilarly strict philosophical terms include Wolfgang Detel, MarcoMesseri, and Antonia LoLordo. In this interpretive tradition, RichardPopkin elegantly poses the global character of the empiricism linkingGassendist philosophy and science. Popkin (1967) ties together twocentral facets of Gassendi’s thought, proposing that the‘constructive skepticism’ at the core of his epistemologyis an attempt (among other things) to show how to have an atomistscience—through inferences based on our data concerningappearances.

The starting point of Gassendi’s philosophy, in Popkin’sview, is skepticism about knowledge of essences, mitigated byallowance for warranted beliefs about appearances and causal knowledgeto which we are entitled just because it helps us to make sense ofbeliefs about appearances. Among the intriguing elements ofPopkin’s assessment is the suggestion that Gassendi promotes anearly prototype of inference to the best explanation (IBE), defendingatomism by appealing to its explanatory value. Gassendi’sstrategy is a bit more complicated, for he cannot grant that theevidence could be equally compelling for all competing theses, givenhis view that atomism is the physical thesis which best makesintelligible our experiential data to begin with. The underlyingmethodological suggestion is that, in considering among physicaltheses, the way we understand and interpret correlative data aboutappearances may depend on which such thesis we are entertaining. Incalling attention to Gassendi’s appeal to IBE, Popkin identifiesa principal challenge in binding together principal themes ofGassendi’s corpus, how to be an atomist and a thoroughgoingempiricist at once (Fisher 2005).

Bibliography

Gassendi’s Principal Works

Exercitationes paradoxicae adversus aristoteleos, in quibuspraecipua totius peripateticae doctrinae fundamenta excutiuntur,opiniones vero aut novae, aut ex vetustioribus obsoletae stabiliuntur,auctore Petro Gassendo. Grenoble: Pierre Verdier, 1624 [BookOne]; Lyon: Laurent Anisson and Jean Baptiste Devenet, 1658 [BookTwo].
Epistolica exercitatio, in qua principia philosophiae RobertiFlvddi medici reteguntur; et ad recentes illius libros, aduersusr.p.f. Marinvm Mersennvm ordinis minimorum Sancti Francisci de Paulascriptos, respondetur. Cum appendice aliquot obseruationumcoelestium. Paris: Sebastian Cramoisy, 1630.
Parhelia, sive soles quatuor, qui circa verum apparueruntRomæ, die xx. mensis Martij, anno 1629: et de eisdem PetriGassendi ad Henricum Renerium epistola. Paris: AntoineVitré, 1630.
Mercvrivs in sole visvs, et Venvs invisa Parisiis, anno 1631:pro voto, & admonitione Keppleri. Paris: Sebastian Cramoisy,1632.
Viri illvstris Nicolai Clavdii Fabricii de Peiresc, senatorisaqvisextiensis vita. Paris: Sebastian Cramoisy, 1641.
De motu impresso a motore translato. Epistolæ duæ.In quibus aliquot præcipuæ tum de motu vniuersè,tum speciatim de motu terræattributo difficulatatesexplicantur. Paris: Louis de Heuqueville, 1642.
De apparente magnitvdine solis hvmilis et svblimis epistolaeqvatvor: in qvibvs complvra physica, opticaque problemata proponuntur,& explicantur. Paris: Louis de Heuqueville, 1642.
Disquisitio metaphysica. seu, Dubitationes et instantiæadversus Renati Cartesii Metaphysicam, & responsa. Amsterdam:Johann Blaev, 1644.
Oratio inavgvralis habita in Regio collegio die nouembrisxxiii. Paris: Louis de Heuqueville, 1645.
De proportione, qva gravia decidentia accelerantvr epistolaetres: quibus ad totidem epistolas R.P. Petri Cazraei Societatis Iesvrespondetur. Paris: Louis de Heuqueville, 1646.
De vita et moribus Epicuri libri octo. Lyons: GuillaumeBarbier, 1647.
Institvtio astronomica, iuxta hypothesis tam vetervm, qvamCopernici, et Tychonis. Dictata à Petro Gassendo …Eivsdem oratio inauguralis iteratò edita. Paris: Louis deHeuqueville, 1647.
Syntagma philosophiae Epicuri cum refutationibus dogmatum quaecontra fidem christianam ab eo asserta sunt. Lyon: GuillaumeBarbier, 1649
Apologia in Io. Bap. Morini librum, cui titulus, Alae tellvrisfractae: epistola IV. de Motu impresso a Motore translato. Vnàcum tribus Galilaei Epistolis de conciliatione … nuneprimùm M. Nevraei cura prodeunt. Lyon: Guillaume Barbier,1649.
Animadversiones in decimum librum Diogenis Laertii: qui est Devita, moribus, placitisque Epicuri. Continent autem Placita, quas illetreis statuit Philosophiae parteis 3 I. Canonicam, …; –II. Physicam, …; – III. Ethicam, … Lyon:Guillaume Barbier, 1649.
Opera omnia… haetenus edita auctor ante obitumrecensuit… posthuma vero, totius naturae explicationemcomplectentia, in lucem nunc primum prodeunt ex bibliotheca…Henrici-Ludovici-Haberti Mon-Morii… [Accessit Samuelis Sorberiipraefatio, in qua de vita et moribus Petri Gassendi disseritur.]Lyon: Laurent Anisson and Jean Baptiste Devenet, 1658

Early Translation and Commentary

François Bernier.Abrégé de laphilosophie de Gassendi. Lyon : Anisson, Posuel et Rigaud, 1684.Reprint edition. Sylvia Murr et Geneviève Stefani, eds. Paris :Fayard, 1992.
Walter Charleton.Physiologia Epicuro-Gassendo-Charltoniana,or, A fabrick of science natural, upon the hypothesis of atoms foundedby Epicurus, repaired [by] Petrus Gassendus ; augmented [by] WalterCharleton. London : Printed by Tho. Newcomb for ThomasHeath…, 1654.

Modern Editions and Translations

Exercitationes Paradoxicae Adversus Aristoteleos (1624).Ed. and trans. Bernard Rochot. Paris: J. Vrin, 1959.
Disquisitio Metaphysica (1644). Ed. and trans. BernardRochot. Paris: J. Vrin, 1964. Cited above as ‘R’.
Opera Omnia. Six Volumes. Reproduction of 1658 Editionwith introduction by Tullio Gregory, Stuttgart-Bad Cannstatt:Friedrich Frommann Verlag, 1964. Cited above as ‘O’.
Pierre Gassendi’s Institutio Logica 1658: a criticaledition with translation and introduction. Ed. and trans. HowardJones. Assen, The Netherlands: Van Gorcum, 1981.
Selected Works. Trans. Craig Brush. (Texts in EarlyModern Philosophy). New York: Johnson Reprints, 1972. Cited above as‘B’.
Pierre Gassendi (1592–1655): Lettres Latines. Twovolumes. [Book VI (Latin correspondence) of Opera Omnia.] Trans.Sylvie Taussig. Turnhout: Brepols, 2004.
Pierre Gassendi, Du principe efficient,c’est-à-dire des causes des choses (Syntagmaphilosophicum. Physique, Section I, Livre IV). Trans. SylvieTaussig. Turnhout: Brepols, 2006.
Pierre Gassendi, De la liberté, de la fortune, dudestin et de la divination (Syntagma Philosophicum, Éthique,Livre III). Trans. Sylvie Taussig. Turnhout: Brepols, 2008.
Pierre Gassendi, Le principe matériel,c’est-à-dire la matière première des choses(Syntagma philosophicum, Physique, Section I, Livre III). Trans.Sylvie Taussig. Turnhout: Brepols 2009.
Gassendi, La Logique de Carpentras. Trans. SylvieTaussig. Turnhout: Brepols, 2012.

Secondary Sources

Selected Books and Collections of Articles

Centre international de synthèse, 1955.PierreGassendi, sa vie et son oeuvre, Paris.
Bellis, Delphine, Daniel Garber, and Carla Rita Palmerino (eds.),2023.Pierre Gassendi. Humanism, Science, and the Birth of ModernPhilosophy, New York and London: Routledge.
Bloch, Olivier, 1971.La philosophie de Gassendi. Nominalisme,matérialisme et métaphysique, La Haye: MartinusNijhoff.
Brundell, Barry, 1987.Pierre Gassendi: from Aristotelianismto a new natural philosophy, Dordrecht; Boston: D. Reidel.
Chalmers, Alan, 2009.The Scientist’s Atom and thePhilosopher’s Stone: How Science Succeeded and Philosophy Failedto Gain Knowledge of Atoms (Boston Studies in the Philosophy ofScience 279), Dordrecht: Springer.
Darmon, Jean-Charles, 1998.Philosophie Épicurienne etLittérature au XVIIè Siècle en France:Études sur Gassendi, Cyrano de Bergerac, La Fontaine,Saint-Evremond, Paris: Presses Universitaires de France.
Detel, Wolfgang, 1978.Scientia Rerum Natura Occultarum:Methodologische Studien zur Physik Pierre Gassendis, Berlin; NewYork: De Gruyter.
Fisher, Saul, 2005.Pierre Gassendi’s Philosophy andScience, Leiden; Boston: Brill.
Gregory, Tullio, 1961.Scetticismo ed empirismo: Studio suGassendi, Bari: Laterza.
Grene, Marjorie and Roger Ariew (eds.), 1995.Descartes andHis Contemporaries: Meditations, Objections, and Replies,Chicago: University of Chicago Press.
Herrera Balboa, Samuel, 2019.Pierre Gassendi. El Proyecto deuna Filosofia de la Naturaleza, Barcelona: Herder Editorial.
Joy, Lynn Sumida, 1987.Gassendi the Atomist: Advocate ofHistory in an Age of Science, Cambridge; New York: CambridgeUniversity Press.
Lennon, Thomas M., 1993.The Battle of Gods and Giants: TheLegacies of Descartes and Gassendi, 1655–1715, Princeton,NJ: Princeton University Press.
LoLordo, Antonia, 2007.Pierre Gassendi and the Birth of EarlyModern Philosophy, Cambridge; New York: Cambridge UniversityPress.
Mazauric, Simone, 1998.Gassendi, Pascal, et la Querelle duVide, Paris: Presses Universitaires du France.
Messeri, Marco, 1985.Causa e Spiegazione: la Fisica di PierreGassendi, Milan: F. Angeli.
Moll, Konrad, 1982.Der junge Leibniz II. Des Übergangvom Atomismus zu einem mechanistischen Aristotelismus: der revidierteAnschluß an Pierre Gassendi), Stuttgart-Bad Cannstatt:Fromann-Holzboog.
Murr, Sylvia (ed.), 1997.Gassendi et L’Europe(1592–1792), Paris: J. Vrin.
Osler, Margaret J., 1994.Divine Will and the MechanicalPhilosophy: Gassendi and Descartes on Contingency and Necessity in theCreated World, Cambridge; New York: Cambridge UniversityPress.
Popkin, Richard, 2003 [1960, 1979],The History of Scepticism:From Savonarola to Bayle, revised and expanded edition, Oxford,UK: Oxford University Press.
Rochot, Bernard, 1944.Les travaux de Gassendi sur Epicure etsur l’atomisme, 1619–1658, Paris.
Sortais, Gaston, 1922.La Philosophie Moderne depuis Baconjusqu’à Leibniz: Études Historiques, Paris:P. Lethielleux.
Sarasohn, Lisa T., 1996.Gassendi’s Ethics, Ithacaand London: Cornell University Press.
Sorell Tom, G. A .J. Rogers, and Jill Kraye (eds.), 2009.Scientia in Early Modern Philosophy: Seventeenth-Century Thinkerson Demonstrative Knowledge from First Principles (Studies inHistory and Philosophy of Science 24) Dordrecht: Springer.
Taussig, Sylvie (trans., intro, annot.), 2001.PierreGassendi: Vie et Mœurs d’Épicure, Paris:Éditions Alive.
Taussig, Sylvie, 2003.Pierre Gassendi (1592–1655):Introduction à la Vie Savante, Turnhout, Belgium:Brepols.
Taussig, Sylvie (ed.), 2008.Gassendi et laModernité (Les styles du savoir 7), Turnhout, Belgium:Brepols.
Wilson, Catherine, 2008.Epicureanism at the Origins ofModernity, Oxford; New York: Oxford University Press.

Biographies

Taussig, Sylvie, 2003.Pierre Gassendi (1592–1655).Introduction à la vie savante, Turnhout: Brepols.
Jones, Howard, 1981.Pierre Gassendi (1592–1655): AnIntellectual Biography, Nieuwkoop: B. de Graaf.
Bougerel Joseph, 1970.Vie de Pierre Gassendi, prévotde l’église de Digne et Professeur deMathématiques au Collège Royal, Paris: JacquesVincent, 1737; Geneva: Slatkine Reprint.

Bibliographies

Bloch, Olivier and Thomas Lennon, 1993. “Gassendi,Gassendismus, Libertinismus”, in Jean-Pierre Schobinger (ed.),Grundriss der Geschichte der Philosophie. Die Philosophie des 17.Jahrhunderts, Band 2: Frankreich und Niederlande, Basel: Schwabe& Co.

Dedicated Journal Issues

XVIIe siècle (Journée d’étudede la Société d’étude du XVIIesiècle) 233 (2006) 4: “Pierre Gassendi”.

Selected Articles or Essays Not Appearing in Collections Listed Above

Alexandrescu, Vlad, 2013. “Regius and Gassendi on the HumanSoul”,Intellectual History Review, 23:433–452.
Begley, Justin, 2023. “Pierre Gassendi (1592–1655):Vegetarianism and the Beatific Vision”, in Andrew Linzey andClair Linzey (eds.),Animal Theologians, Oxford and New York:Oxford University Press, 25–43.
Bloch, Olivier René, 1966. “Gassendi critique deDescartes”,Revue Philosophique de la France et del’Etranger, 156: 217–236.
Bloch, A.G., 1963. “Pierre Gassendi and his ScientificExpedition of 1640”,Archives internationalesd’histoire des sciences, 63: 133–134.
Forgie, J. William, 2007. “Gassendi and Kant onExistence”,Journal of the History of Philosophy, 45:511–523.
Galluzzi, Paolo, 2000. “Gassendi and l’AffaireGalilée of the Laws of Motion”,Science inContext, 13: 509–545.
Garau, Rodolfo, 2021. “Who was the Founder of EmpiricismAfter All? Gassendi and the ‘Logic’ of Bacon”,Perspectives on Science, 29: 327–354.
Johnson, M. R., 2003. “Was Gassendi an Epicurean?”,History of Philosophy Quarterly, 20: 339–360.
LoLordo, Antonia, 2005. “Gassendi on Human Knowledge of theMind”,Archiv für Geschichte die Philosophie, 87:1–22.
Michael, Fred, 1997. “Why Logic Became Epistemology:Gassendi, Port Royal, and the Reformation in Logic”, inLogic and the Workings of the Mind: The Logic of Ideas and FacultyPsychology in Early Modern Philosophy (North American KantSociety Studies in Philosophy 5), ed. Patricia A. Easton, Atascadero,CA: Ridgeview Publishing Company, 1–20.
Michael, Emily and Fred S. Michael, 1989. “Two Early ModernConcepts of Mind: Reflecting Substance vs. Thinking Substance,”Journal of the History of Philosophy, 27: 29–48.
Michael, Emily and Fred S. Michael, 1991. “Hierarchy andEarly Empiricism,” inAntifoundationalism Old and New,ed. Beth Singer and Tom Rockmore, Philadelphia: Temple UniversityPress.
Paganini, Gianni, 1989–1990. “Epicurisme etphilosophie au XVIIe Siècle, Convention, Utilité etDroit selon Gassendi”,Studi Filosofici,XII–XIII: 5–45.
Palmerino, Carla Rita, 2004. “Gassendi’sReinterpretation of the Galilean Theory of Tides”,Perspectives on Science, 12: 212–237.
Popkin, Richard, 1967. “Gassendi, Pierre,” inTheEncyclopedia of Philosophy, ed. Paul Edwards, New York: Macmillanand the Free Press, Volume 3, 269–273.
Rochot, Bernard, 1971. “Pierre Gassendi”,Dictionary of Scientific Biography, ed. Charles S. Gillespie,New York: Scribner.
Sakamoto, Kuni, 2009. “The German Hercules’s Heir:Pierre Gassendi’s Reception of Keplerian Ideas”,Journal of the History of Ideas, 70: 69–91.
Willis, Wes, 2003. “The Vibrating Nerve Impulse in Newton,Willis and Gassendi: First Steps in a Mechanical Theory ofCommunication”,Brain and Cognition, 51:66–94.

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Other Internet Resources

Catalogue du Fonds Gassendi – Oeuvres, biographies, études critiques, articles de revues scientifiques, hosted by the Médiathèque intercommunale des TroisVallées (Digne-les-Bains)
Pierre Gassendi, The British Museum
Pierre Gassendi (1592–1655), Bibliothèque nationale de France
Pierre Gassendi, J.J. O’Connor and E.F. Robertson, for the MacTutor History ofMathematics Archive (University of St Andrews)

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