Moritz Schlick

First published Tue May 28, 2013; substantive revision Fri Oct 13, 2017

Although Moritz Schlick (1882–1936) made a lasting mark in thephilosophical memory by his role as the nominal leader of the ViennaCircle of Logical Positivists, his most lasting contribution includesa broad range of philosophical achievements. Indeed, Schlick’sreputation was established well before the Circle went public. In1917, he publishedSpace and Time in Contemporary Physics, aphilosophical introduction to the new physics of Relativity which washighly acclaimed by Einstein himself as well as many others. Thefollowing year, the first edition of his influentialGeneralTheory of Knowledge appeared and, in 1922, he was appointed tothe prestigious chair ofNaturphilosophie at the Universityof Vienna. Upon his arrival at his new post, he immediately began tocollaborate with the mathematician Hans Hahn, the sociologist andeconomist Otto Neurath, forming a discussion group known as the‘Schlick Zirkel’. In the 1930s, the intellectualenergy of the Circle was increased by newcomers like Rudolf Carnap andKurt Gödel, as well as the outside influences of thinkers fromAmerica (Ernest Nagel, W. V. O. Quine), Britain (A. J. Ayer), Poland(Alfred Tarski), and Germany (Hans Reichenbach), put Schlick in themidst of a virtual whirlwind of philosophical activity which deepened,broadened, and matured his thinking. As his international fame grew,Schlick found himself lecturing in London, teaching at Stanford, andreceiving offers to join the faculties of prestigious universitiesboth at home and abroad. At the same time, he produced a number ofessays which exerted a deep and lasting influence on contemporarythought. But Schlick’s life was cut short by an assassin’sbullets in 1936, much to the loss of the intellectual world.

1. Background

Moritz Schlick is primarily remembered as the leader of the ViennaCircle of Logical Positivists, which flourished in the early1930s. Few philosophers of science today would deny thattheir views have been influenced – one way or the other – by thepositions which emerged from the group of philosophers, mathematicians,and social scientists who gathered in between-wars Vienna. Andwhile it cannot be denied that other Circle members were more prominentand influential over the long-term, none contributed more unity andcohesion to the Vienna group during its brief existence. Indeed,long before 1930, when the Circle’s Manifesto,“Wissenschaftliche Weltauffassung: Der WienerKreis”, appeared, Schlick had already made contributions toscientific epistemology which exerted a profound influence onsubsequent generations of philosophers (Neurath 1973, Ch. 9). And whileother Circle members quite deservedly continue to receive a great dealof attention, there has always been a steady interest inSchlick’s views on a range of issues, for there is much oflasting value to be discovered in them.

Schlick was born in Berlin in 1882 and grew up as the son of amiddle-class factory manager. Aftergymnasium, heattended the University of Berlin, intent from the start to studyphysics. His ambition led him to work with Max Planck and hereceived his Ph.D. in 1904. After a year of experimental work atGöttingen, he eventually made his way to Zurich where he took upthe study of Philosophy. In 1910, he secured a position atRostock, moving on to Kiel before assuming the Chair ofNaturphilosophie at Vienna in 1922. Through all thesechanges, as well as subsequent modifications of his thought, theevidence of Schlick’s training in Berlin remained just below thesurface. Schlick was, after all, the heir apparent to thetradition of philosophical physicists, a tradition founded by Hermannvon Helmholtz, the icon of 19th Century physics and an influentialleader of thezurück zu Kant movement, and continued byhis student and (later) colleague Planck (Coffa 1991, 179–183). Although few professional philosophers embraced the methods andproblems of the philosophical physicists, they were highly influentialthroughout the community of professional physicists, largely due totheir prestige.

2. The Philosophical Physicists: Helmholtz and Planck

Although Schlick was originally trained in Physics, it is importantto remember that, in late 19^th Century Germany, physicistswere deeply interested in philosophical issues, especially atBerlin. Schlick was the intellectual heir of bothHermann von Helmholtz,a major figure among 19^th Century physicists and achampion of thezurück zu Kant movement and MaxPlanck. In 1889, Planck succeeded Gustav Kirchhoff and becameHelmholtz’ colleague. Both Helmholtz and Planck integratedKantian themes in their philosophical thinking and there can be nodoubt that, even though Schlick could never be considered much of aKantian, he was deeply sympathetic with many of Kant’sideas. To begin with, Kant’s interests in epistemologicalconcerns arising from the advanced mathematical sciences attractedSchlick’s admiration and respect, much as it had drawn theinterests of Helmholtz and Planck. And all three embraced thegoal of developing a philosophical understanding of recent developmentsin physical science in the spirit, if not the letter, of Kant’sthought. For the most part, their departures from Kant’soriginal doctrines may be viewed as innovations or improvements ofKant’s insights, introduced without abandoning their own mostfundamental philosophical commitments.

For instance, one of Helmholtz’ most well-known innovations isthe study of perception in his monumentalHandbook of PhysiologicalOptics (1856–1867) (Helmholtz 1924–5). This work was thesource of his so-called ‘sign-theory’, based on the ideathat perceptions are signs or place-holders for what they signify, butdo not resemble or copy them in any way. In his early writings,Helmholtz thought sensations are signs of their external causes, so theassociations among sensations represent corresponding regularitiesamong their sources. Consequently, it is the regular changes ofsigns, their serial structure, which reflects the order of theirunderlying causes. But this latter consequence implies a causaltheory of perception which is fundamentally antithetical toKant’s understanding of causality. After all, Kant hadrestricted the operations of causality to the realm of appearances,thus excluding unobservable causes lying behind and causing observablephenomena. But this departure from a basic tenet of Kant’sthought was compounded by the fact that Helmholtz’ account of theknowledge of the location of objects in space is thoroughly empiricist,and also rests on the principle of causality, understood as a causalrealist would. But in his 1881 notes to his memoir, Helmholtzcorrected himself, recalling that Kant’s views on causality werelimited to lawfulness among appearances (Friedman 2010, 631; Friedman1997, 30–1). What Helmholtz then asserted, in his classic essay“On the Facts of Perception,” is that the inference to ahypostasized reality lying behind the appearances goes beyond what iswarranted by the lawfulness obtaining among appearances. Indeed,all localizations of objects in space are really nothing more than thediscovery of the lawfulness of the connections obtaining among ourmotions and our perceptions. The difference between what isgenuinely perceived and its realistic interpretation is just thedifference between the regularities in our perceptions and thehypothesis of enduring, substantial sources of the perceivedregularities (Helmholtz 1977, 138–140).

Although Helmholtz’ philosophical work was not particularlywell-received by professional philosophers likeHermann Cohen,co-founder of the Marburg School of neo-Kantians, it exerted a powerfulinfluence on physicists (Cohen 1885, 202–204). In particular, MaxPlanck was an early supporter of the sign-theory. But Plancknever interpreted the sign-theory causally, like Helmholtz had in hisearliest writings. Rather, Planck recognized that “ourperceptions provide, not a representation of the external world”but, rather, “measurements furnish the physicist with a signwhich he must interpret” (Planck 1960, 53; Planck 1933,84). Furthermore, Planck generalized the sign-theory, arguing thatit is not objects, in and of themselves, which are known, but thestructural relations in which they stand to one another. Hisfundamental idea was that what is known are not the natures of‘things’ but complex structures of relations connecting‘things’ to one another (Planck 1933, 84ff. and 1960,53). Thus, the ‘objects of knowledge’ are not objectsat all but, rather, what is known are the relata of the structuralnetworks of relations in which they stand to other relata. And,as recent developments have increased the level of abstraction ofscientific thought, it has become further removed from itsanthropomorphic origins. So the unification of the scientificworld-picture is achieved through increasing abstraction which, inturn, drives structural representation, thus reducing theanthropomorphic elements in the scientific image of theworld (Planck 1949, 105). The result ofPlanck’s effort is a theory of knowledge which is structuralist,generalized from Helmholtz’ sign-theory of perception, but whichnonetheless preserves the themes of unification and objectivity derivedfrom Kant.

These themes are particularly evident in Planck’s celebrated(1908) Leiden lecture on “The Unity of the PhysicalUniverse”, directed at Ernst Mach’s phenomenalisticNaturphilosophie (Planck 1960, 1–26). Without going intodetails, Mach regarded physical objects as unnecessaryhypostasizations, implying that the mechanical view underlying physicsis little more than an elaborate myth. The physics of the matterwere effectively settled when Planck secured the mechanical foundationsof irreversibility in his Radiation Law of 1900 by relying on LudwigBoltzmann’s statistical approach to thermodynamics which, inturn, implied atomism. Yet it remained to establish thephilosophical implications of these achievements. In his Leidenlecture, Planck argued that this result presented an objectiveworld-picture abstracted from its anthropomorphic origins to produce asynthetically unified image of the world (Planck 1960, 6). Such a view, Planck argued, canonly be produced through the unification of the diverse fields ofphysical phenomena if they are synthesized by means of mathematicalabstraction. Such abstraction generalizes the sign-theory toapply to theoretical as well as perceptual representations, resultingin a full-blown structuralist epistemology (Planck 1933, 84ff.; Planck1949, 105). And it is this method of abstraction thatproduces the synthetic unity grounding scientific objectivity. The result is that physical entities are ‘objective’, inthe Kantian sense, since they embody the lawfulness ofappearances. Indeed, Planck insisted that what is‘objective’ is precisely what the heroes of the history ofscience, from Copernicus to Faraday, would have regarded as‘real’ (Planck 1970, 25–6). Despite thestrident Kantian themes of Planck’s argument, his conclusion hasalways been regarded as a particularly virulent form of convergentrealism (Stölzner 2010).

3. Early Epistemology

Emerging from the tradition of the philosophical physicists,Schlick’s early thought bears the marks of his intellectuallegacy. After the completion of his graduate study in physics,Schlick soon turned his attention to philosophy (Schlick 2006a). Within a few short years he had written a youthfully enthusiasticethical tract in 1908, calledLebensweisheit, a lucid analysisof concept-formation called “The Boundaries of Scientific andPhilosophical Concept-Formation” (1910), as well as a substantialessay on “The Nature of Truth in Modern Logic” (1910)(Schlick 2006b; Schlick 1979a, 25–40, 41–103). In “TheBoundaries…”, Schlick provided a broad sketch of hisunderstanding of scientific thought, which identifies the aim ofscience as the reduction of phenomena to relationships governed by law,thus exhibiting individual events as special cases of universal,exceptionless regularities. Science is expressed mathematically, inspatio-temporal form to provide for exact measurement. And theindividual sciences are demarcated by distinctive intensive qualities,as ‘mass’ distinguishes mechanics, ‘heat’thermodynamics, etc. Although the methods of mathematico-scientificconcept-formation reduces the entire natural world to purelyquantitative relations, it is powerless in the face of irreducible purequalities. This is the task of philosophy so that philosophybecomes thetheory of qualities. Schlick’s work on“The Nature of Truth in Modern Logic” not only provides abroad survey of treatments of truth then current in German philosophy,but it also introduces an original view of truth as univocaldesignation. A judgment, as a structured complex of itsconstituents, is coordinated with the fact which consists of theentities signified by the judgment’s constituents, arranged in away which is coordinated with the structure of the particularjudgment. When the constituents are structured in a judgment sothat the whole judgment univocally designates a situation in the world,then the judgment is true; otherwise, it is false. The conceptionof truth as univocal coordination figured prominently inSchlick’s pre-Positivist theory of knowledge.

The centerpiece of Schlick’s early epistemology is a deepcleavage between intuitive acquaintance and conceptual knowledge. Although Schlick’s distinction is reminiscent of Kant’scontrast between intuitions and concepts, Schlick regarded intuition asfully naturalized, much as Helmholtz had. When the elements ofjudgments are initially identified, they are grasped qualitatively, assensory impressions, like the visual image of a particular dog or thememory image of a horse. These intuitions of acquaintanceare spatially qualitative, since they are not only extended butsituated with respect to one another in the space of the particularsensory modality through which they are perceived. They are alsotemporal, since they succeed one another in time. For an example,Schlick considered the visual image of something in the distance which,as it approaches, is identified, first of all, as an animal, then it isrecognized as a dog and, when it comes close enough, it will berecognized as my dog ‘Fritz’. Each of these casesinvolves the recognition of one thing – the image of that which isapproaching – as something else, an animal, a dog, and (finally)Fritz. Thus, each of these cases involves knowledge that theimage is that of an instance of some class (Schlick 1979a, 119–121;Schlick 2009, Sec. 2). And the same process, in which one thing isrecognized as another and therefore known, occurs in cases ofscientific knowledge. For instance, the early explanations oflight recognized that its behavior was much the same as the behavior ofwaves. Thus, in the work of Christian Huyghens, light came to beknown as a wave phenomenon or, in other words, as the wave-likepropagation of a state. Later, through the work of HeinrichHertz, it was realized that light was unlike mechanical waves whichtraveled through a medium (such as water or air) but, rather, lightbehaved more like electrical waves. Accordingly, light becameknown as an electromagnetic wave phenomenon. In this case, as inthe everyday case of the knowledge that the approaching animal is mydog Fritz, light was originally known as a wave phenomenon and onlylater did it become known as an undulatory disturbance in anelectromagnetic field (Schlick 1979a, 121–2; Schlick 2009, Sec.3).

In the early stages of everyday knowing, what is re-discovered orrecognized when something is known is an intuitive idea. Intuitiveideas present images which are signs of their contents and are drawnfrom sensory experience. Of course, images are vague, blurred, andill-defined so that when one conjures up an image, say, of one’sfather, the expression on his face may not be clear and distinct, so that itmay be impossible to tell whether he is frowning or merely lookingpuzzled (Schlick 1979a, 126–7; Schlick 2009, Sec. 4). And whileintuitive ideas are sufficient for the purposes of everyday life,scientific inquiry naturally demands more rigorous methods forcapturing and expressing ideas. For this reason, concepts –ideas with precisely delineated contents – are used. And whilethe meanings of terms used in everyday discourse are usually intuitiveideas, in science they are almost exclusively concepts. This providesscientific judgments with content which is accurately circumscribed,while at the same time eliminating their intuitive content. InhisGeneral Theory of Knowledge of 1918, Schlick explainedthat concepts are formed in clusters, just as the primitive conceptsof a mathematical field are defined in terms of one another by theaxioms of the discipline. But in his earlier epistemological writings,he explains concept-formation in a more traditional fashion, byreference to marks or characteristics (Merkmale) which belongto all the objects which fall under the concept. Concepts thusrepresent classes of objects, defined in terms of determinate traits,so that their scope is exactly demarcated. Thus they differ fromintuitions, which are indistinct representations of what is presentedto a particular sensory modality. So the intuition of a triangle ingeneral or a man in general can only be a hazy, fuzzy-edged visualrepresentation of some particular triangle or man. And while everydayknowing proceeds by comparisons of intuitions, scientific knowledgereplaces intuitions in these comparisons with precisely delineatedconcepts. In short, it is through its reliance on concepts thatscientific thinking takes knowledge to a higher level than everydayknowing.

Thus, in his earliest philosophical writings Schlick introduced aninnovative conception of truth as univocal designation and affirmed acontrast between intuitions and concepts which was ultimately derivedfrom Kant and naturalized by Helmholtz. Soon, Schlick waspresented with an opportunity to display his scientific acumen, byexplaining the philosophical import of Special Relativity.

4. Special Relativity

Schlick availed himself of the opportunity to elaborate hisepistemological views in application to the new physics of Relativityin his 1915 essay on “The Philosophical Significance of thePrinciple of Relativity” (1979a, 153–189). This essayis particularly significant in Schlick’s development since itfirst presented certain philosophical tenets which would figure in allhis subsequent work. Implicit in the general philosophical schemein which Schlick discussed Relativity is an objective, logicaldistinction between the representational framework in which scientificclaims may be formulated and those claims themselves. Anintrinsic function of the representational scheme is the constitutionof the very concepts in which the formulation of empirical claims isfirst made possible. Moreover, since the same empirical claimsmay be expressed in distinct representational schemes, the contentwhich is expressed by all the differing conceptual frameworks comprisesthe common, objective content of scientific assertions. Incontrast, what varies from one description to another reflects thefeatures of the representational systems which distinguish them fromone another.

Schlick applied these insights to the fact that no physical meanssuffice to distinguish inertial frames or, in other words, no (uniform,rectilinear) motion can be detected relative to the ether. Thereare two alternative responses to this situation. The firstalternative, due to Lorentz and Fitzgerald, accommodates experimentalfindings through the postulation of compensating contractions of movingbodies in the direction of motion. Buttressed by additionalauxiliary hypotheses, the Lorentz-Fitzgerald hypothesis preserves theabsolute space and time of Euclid and Newton, as well as Galileankinematics, while explicating experimental failures to detect theabsolute rest of the ether by positing a real effect of absolute motionon length. The alternative presented by Einstein in the SpecialTheory was simply to deny the presupposition of an absolute timereference, allowing that two spatially separated events may betemporally ordered in one way for a given system of reference and mayalso be ordered differently for a distinct, yet equally legitimatesystem. Contractions of length are then a consequence of therelativity of reference frames: the length of a measuring rod dependson its velocity for a given frame of reference (Schlick 1979a,160–1). Consequently, the facts of observation are accommodatedequally well by the Principle of Special Relativity as they are by theLorentz-Fitzgerald hypotheses. In other words, they areequivalent or “both theories do the same thing”. (Schlick 1979a, 162) The principal advantage of Einstein’sapproach is that his solution is clearly the simplest. At thisjuncture, it should be noted that Schlick did not argue that the choicebetween the available alternatives is conventional because they areempirically equivalent, implying all the same observationalconsequences. Rather, Schlick repeatedly urged that there is anunderlyingphysical equivalence from which the empirical orobservational equivalence follows. And the fact that it is thephysical rather than observational equivalence which serves as premiseof his argument is especially evident from his use of his earlieranalysis of the concept of truth to explicate the equivalence.

Schlick thought the situation in physics presented a thorough-goinganalogy with Poincaré’s treatment of the conventionalityof geometry. Schlick noted, first of all, thatPoincaré’s geometric conventionalism was founded on theKantian insight that it is only the behavior of bodies in space thatforms the object of study, so that the resulting physics is “theproduct of two factors, namely the spatial properties of bodies andtheir physical properties in the narrower sense” (Schlick 1979a,169; Cf. also 1979a, 230–233). The point of Schlick’sreference to Poincaré is to illustrate the particular variety ofconventionalism operative in Poincaré’s treatment ofgeometry, in order to apply it to the case of Special Relativity. And just as Poincaré isolated two factors in the treatment ofthe motion of rigid bodies, in general any true theory may be regardedas the product of a reference-system, or representational scheme, andthe judgments formulated in that system. Since there arealternative ways of securing univocal coordination, the components withrespect to which distinct but equivalent representations differ areartifices of the representational scheme. Parting fromPoincaré, Schlick recognized that the representational frameworkthat appears simplest when regarded in isolation may nonethelessrequire excessively complicated formulations for the description ofreality. And he insisted –contraPoincaré – that it is the simplicity of these formulations thatis the most compelling desideratum, not the simplicity of therepresentational scheme. Thus, the representational scheme thatallows for the simplest description of reality is always to bepreferred – so much the worse for Euclid, and Poincaré,too.

5. General Theory of Knowledge

Schlick’s earlier epistemological insights, as well as theconventionalist framework developed in his work on the Special Theory,set the stage for his thought in the two works which distinguish hispre-Positivist era:General Theory of Knowledge (largelycomposed in 1916, with its first edition appearing in 1918 and thesecond edition in 1925) andSpace and Time in ContemporaryPhysics. (Engler 2009, 130 fn. 51) (Spaceand Time … appeared for the first time in 1917 as anextended essay in the prestigious journal,DieNaturwissenschaften; soon it was re-issued in three more editionsand eventually translated into eleven languages). Beforeexplaining how Schlick’s epistemology embraced the new physics,it is necessary, first of all, to consider how he further developed hisearlier epistemological insights.

General Theory is notable for a key innovation in itstreatment of concepts, for they are defined in terms of mathematicalequations rather than reducing them to complexes of intuitive images(Schlick 2009, Sec. 5). In order to articulate his ideas about thenature of concepts and how they are formed, Schlick borrowed the ideaof definition by axioms from recent work in the foundations of geometryby Moritz Pasch, David Hilbert, and Henri Poincaré. In theirwork on alternative geometries, these mathematicians came to regard theeffects of altering the axioms of geometry as changing the meaning oftheir constituent terms, thus re-defining the primitive geometricconcepts. The idea is ingenious in its simplicity, for it treatsthe geometric primitives as defined by the relations they bear to oneanother according to the axioms, so the meanings of the terms‘point’, ‘lies between’, and ‘liesupon’ are fixed by the geometric axioms. The reasonmathematicians adopted this method is to insure the certainty ofgeometry by insuring that it was invulnerable to the criticism that itsprimitive elements were defined by intuition.

Schlick claimed the method of definition by axioms was implicitbecause, unlike explicit definition, occurrences of the defined termcannot necessarily be replaced by a combination of the expressions which defineit. And he praised the method for its specification ofmeanings independently of any intuitive content. Implicitlydefined terms possess a clarity and precision of scope which cannot beachieved by concepts defined by abstraction fromexperience. Since, of course, axiomatic definitionsstipulate the meanings of all their constituent concepts in terms ofthe remaining ones, the axioms effectively define concepts by theirrelations to one another. Thus implicit definitions arestructural definitions, and their constituent terms are structurallydefined (Schlick 2009, Sec. 7). The concepts thus defined areonly related to the other elements of the axiom system and are notrelated to anything external to the axiom system until the definitionis coordinated with extra-linguistic things. In Schlick’searlier writings, he had stated that concepts themselves are functionswhich signify or designate the items with which they are coordinated orassociated. Accordingly, even implicitly defined concepts must becoordinated with objects, elements of the class of things to which itapplies (Schlick 1979a, 130; Schlick 2009, 23; Ryckman 1991,Sec. 3). Of course, these objects, like the concepts whichdesignate them, are distinguished by possession of the properties interms of which the designating concepts are defined. Suchcoordinations give empirical content to implicitly defined concepts,transforming them into full-blooded concepts rather than emptyplace-holders. Moreover, the concepts which dominatescientific thought at any given stage of its development must bemodified, revised, and supplemented as science advances. Then aconceptual characterization of a given phenomena which was used at anearlier stage may not be at a later stage as, for instance, thejudgment ‘A light-ray consists of a stream of movingparticles’, drawn from Newtonian optics was later replaced by‘A light-ray consists of electromagnetic waves’.

Schlick’s new understanding of concept-formation allows him toseriously address the question of how the respective intuitive spacesof each of the senses are coordinated in the construction of a generalintuitive space, which is not specific to any particular sensemodality. The intuitive images of experience are spatiallyordered, since they exhibit relative locations as well as spatialextension. In addition, since experiences occur one afteranother, they also exhibit an intuitive temporal order. Thisresults in a distinct spatio-temporal ordering for each of the sensemodalities, so that an intuitive order of smells, as well as anintuitive order of tastes (and so forth) are given inexperience. The first step in the advance from purelysubjective experiences to the transcendent reality of scientificobjects is to coordinate the spatio-temporal frameworks of the distinctsense modalities. Thus, when a sore spot on one’s leg istouched by one’s forefinger, the feeling of the touch isaccompanied by a visual image of the finger touching the leg. Thecoincidence of these two separate and distinct types of sensory datacontributes evidence to the overall coordination of the spatio-temporalorders of the different sense modalities. This is themethod of point-coincidences which Schlick applied to characterize theadvance to knowledge of the transcendent world from the purelysubjective domain of qualitative images. Of course, the idea ofpoint-coincidences also plays a central role in General Relativity andit has generally been assumed that Schlick picked up the idea from hiswork on the new physics. But recent scholarship has demonstratedthat, in fact, Schlick worked on the notion long before Einsteinpublished the General Theory and may well have been Einstein’ssource of the notion (Engler 2009, 135ff). The importantpoint in the present context is that the coordination of a singleindividual’s sense modalities is but the first step in theconstruction of the transcendent order. The next phase consistsof the coordination of point-coincidences among differentindividuals. If an instructor wishes to draw attention to somefeature of a triangle on a blackboard at the front of a class, hepoints to the feature, thus effecting a point-coincidence between thetip of his finger and the feature of the triangle. And eventhough everyone witnessing the demonstration has a differentperspective, what they all share is their observation of thepoint-coincidence of finger-tip and the geometric feature. Further, it is to be noted that not every sensory point-coincidence isan objective one and it is generally true that not every objectivepoint-coincidence is observed directly but is constructed or inferredfrom ones that are. Finally, all measurements, all determinationsof space and time, are based on just such spatio-temporalpoint-coincidences (Schlick 2009, Sec. 31).

Earlier Schlick had argued that knowledge consists in theidentification of that which is known with that as which it is knownor, in other words, knowledge consists in the relation of onething to some other thing, as which it is known. And this is onlyachieved when one of the objects which is known is, in turn, related tostill others, as it is in the myriad spatio-temporal relations in whichit stands to other objects. Ultimately, all these relations canbe known quantitatively by specifying a number of magnitudes, thusreducing the relations of the objective spatio-temporal order toquantities. Of course, this cannot be achieved within thequalitative order since the different relations of position andtemporal order are qualitatively different and cannot, for that veryreason, be compared. But the entities populating the objectivespatio-temporal order are wholly unlike the denizens of the subjectiverealm which are the intuitive objects of experience, the immediatelygiven sensory data. Both may be univocally designated byimplicitly defined concepts and both kinds of entities are, therefore,objects of possible knowledge. As such, intuitive contents areattributed full reality and, in addition, the objects populating thespatio-temporal order, the entities of advanced theoretical science,are just as real as the contents of consciousness with which they arecorrelated.

Schlick expended considerable effort discussing the differences betweenintuitive acquaintance and conceptual knowledge, insisting that, eventhough intuitive images are real, acquaintance with them does notconstitute knowledge. This thesis directly confronts the idea,held by a number of philosophers, that acquaintance with intuitivecontents is, indeed, a species of knowledge which is more direct andimmediate than conceptual knowledge. By comparison, scientificknowledge is regarded as a poor substitute, lacking the intimacy ofintuitive acquaintance. Two champions of this belief areHenri Bergson,whothought that direct access to intuitive contents could (somehow)‘unite’ the knower with the object known, andEdmund Husserl,whoproposed that a genuinely philosophical intuition could become thebasis of a kind of scientific cognition in which the subject is indirect contact with its object, without any symbolism or mathematics,any inferences or proofs (Bergson 1955; Husserl 1965). Bergson called this intimate perception of objects‘intuition’ and Husserl called it‘wesenschau’. But the reason why intuitioncan never constitute knowledge is, of course, quite obvious toSchlick. On his view, knowledge requires two terms: that which isknown and that, as which, it is known. But intuition, consideredas an act of consciousness, involves only that which is intuited. In short, the attempt to identify intuition as a form of knowledge issimply a conflation of knowledge with acquaintance, of unelaborated,direct perception or sensation with conceptual knowledge, ofkennen witherkennen (Schlick 2009, Sec. 12).

Schlick’s discussion of the differences between intuition andknowledge laid the groundwork for his treatment of realism. Hecautioned, at the outset of his discussion, that the question ofrealism is not a philosophical problem, but an everyday one. Andthe view that guides the comings and goings of ordinary life isnaïve realism, which assumes that reality consists simply of theobjects of sense perception. Of course, the demands of day-to-dayaffairs seldom require any distinction between the perception of anobject and the object perceived, until one encounters an illusion whichdemands the differentiation of, say, a mirage from a puddle orpond. Only then is a representation first distinguished from itsobject. It is at this point that the ordinary person realizesthat the mirage was real but that the pond or puddle was not. Thus refined, the naïve criterion of reality is extended beyondthe reach of the senses once it is realized that, even when an objectis not perceived, its effects provide a sufficient condition of itsreality, as when a hunter finds a ravaged animal in the forest andconcludes that a predator is in the neighborhood. And it is inprecisely this way that naïve realism is naturally extended toinclude, not just perceptions themselves as well as the objectsperceived, but also the causal sources of observed effects. Inthis way, naïve realism naturally leads to classical causalrealism.

Then it simply becomes useful to refer to those objects which are notgiven in sensory experience – or at least not presently given– as ‘things-in-themselves’ since they are, by thecausal criterion, real. Things-in-themselves are just the transcendententities of the objective, three-dimensional world of everydaymaterial objects, as well as the unobservable, theoretical entitiespostulated by contemporary science. Unsurprisingly, the reality ofthese entities is contested by a variety of related views, whichSchlick classifies as ‘immanence’ philosophies. The mostprominent immanence view is the kind of phenomenalism found inthinkers from John Stuart Mill to contemporaries like Joseph Petzoldt,Ernst Mach, and (as Schlick added in the second edition ofGeneralTheory …), Bertrand Russell. More curious, perhaps, isthat Schlick also indicted his intellectual forebear, Hermann vonHelmholtz, as an immanence philosopher. Basically, these thinkers allrestrict reality to the given, so that reality consists exclusively ofcolors, tastes, and smells, as well as other sensations, presented inconstantly changing combinations with one another. This is, of course,just to deny the reality of transcendent objects, thus abjuring thecausal realism implicit in everyday and scientific talk oftranscendent objects which exist and endure beyond momentarysensations. Instead, the immanence thinkers claim that all talk oftranscendent objects consists entirely of discourse about complexes ofsensations which exhibit more stability and constancy thanothers. Mach stated the common view of immanence philosophies thatmaterial bodies do not produce sensations, because bodies are, atbottom, nothing more than complexes of sensations (Schlick 2009, Sec.25). Of course, immanence views differ among themselves in theirefforts to identify which particular complexes of sensation areidentified with everyday material bodies and scientific entities,especially when the latter are not perceived.

The classic immanence view is one which identifies material bodieswith the combinations of sensations which would appear, in a givensituation, if a perceiver were present. Of course, this is justJohn Stuart Mill’s definition of bodies as ‘permanentpossibilities of sensation’ – a treatment which persists inthe writings of many of his followers, in one form or another. For instance, Bertrand Russell, inOur Knowledge of the ExternalWorld, calls the stable combinations ‘aspects’,declaring that “Things are those series of aspects which obey thelaws of physics” (Russell 1922, 110). Specifically, Russellargued that so-called ‘ideal aspects’ – ones which arenot presently perceived – may be logically constructed from those whichare. Their reality may then be readily assumed. But withthis assumption, any grounds of distinguishing between given aspectsand assumed ones vanishes, nor is there any means of recovering them,without complicating the system beyond all recognition. Schlicknoted that, because of Russell’s sheer audacity in pushing hisaccount to the limit, the result is not prone to the inconsistencieswhich plague other accounts. Indeed, it is undeniable thatRussell’s “bold position” is one of the mostsuccessful efforts to carry out the immanence philosophy (Schlick2009, 502). In a different vein, Joseph Petzoldt acknowledged thatesse is not the same aspercipi, though he thenendeavored to identify the existence of objects with some limited groupof sensations, a different group for each perceiver. Despite thecountless problems this approach encountered, the critical point whichPetzoldt missed is simply that it is impossible to simply identify anyparticular sensation or group of sensations with a material body,without further conditions relating the sensation or sensations (as,for instance, Russell provided) (Russell 1922, 106). Andthat is because it is the lawful regularity among sensations whichwarrants the collection of the series of changing sensations under asingle material body. Mach very nearly realized this when, inThe Analysis of Sensation, he abandoned Mill’s‘possibilities’ and replaced them with the mathematicalnotion of a functional relation. But such a purelymathematical idea can never be substituted for an empirically-basedconcept of reality. Such efforts are, at bottom, attempts toconceptually embody a law, as epitomized in Helmholtz’ “TheConservation of Force: A Memoir” (Kahl 1977, pp. 49–50). Specifically, Helmholtz identified the objective power of a law withforce, thus reducing the reality of material bodies and scientificentities to a conceptual substitute. But concepts, according toSchlick, can never possess the reality of the contents of consciousnessor transcendent things-in-themselves (Schlick 2009, Sec. 25).

6. Relativity

In correspondence with Einstein, Schlick explained that hismonograph onSpace and Time in Contemporary Physics was“less a representation of the general theory itself than athorough-going elucidation of the thesis that space and time have nowforfeited all objectivity in physics” (Schlick 1917). Ofcourse, Schlick is referring to Einstein’s remark in his 1916paper on the General Theory, that the admission of arbitrarycoordinative transformations “removes the last vestige ofphysical objectivity from space and time” (Einstein 1916,117). In his monograph, Schlick first described the differencesbetween the space of the older physics and the space postulated byEinstein. In Newtonian physics (as well as the physics of theSpecial Theory), all measurement was founded on the notion of a rigidrod and space was still regarded as Euclidean so long as measurementswere made within the same coordinate system. Thus, in the olderphysics, space was conceived as complete with metrical properties,defined by rigid rods which possess the same length in any place at anytime. It is particularly to be noted that the metrical propertiesof space were regarded as independent of the distribution of bodies inspace and their gravitational fields. It is precisely theseconditions that are changed in General Relativity. Rather, in theGeneral Theory, the principle of general covariance implies thatproperties cannot be ascribed to space independently of anyconsideration of the things in it. Einstein showed thatnon-Euclidean methods of determining measurements must be used in thepresence of a gravitational field and this follows from the insightthat it is the things in space which give it a particular structure.The result is a complete relativization of space (Schlick 2006a, Sec.VII).

In classical mechanics, it was decided by convention (see above)that a rigid rod was the same length throughout space and thisconvention was modified in Special Relativity. But in GeneralRelativity, the length of a rigid rod may also depend on its place andposition in such a way that consistency with Special Relativity ismaintained. Thus, to maintain the general postulate ofrelativity, it is necessary to reduce the objective spatial structureof the earlier physics to a non-intuitive topology. This is aradical departure from the objectivity of the spatial structure ofthese earlier systems, which was entirely an artifact of their fixedmetrical structure. But in Relativity Theory, the resultingconceptual construction admits of distinct metrical structures indifferent regions depending on the gravitational field in that region.As Schlick reflects in the closing pages ofSpace and Time…, the very possibility of the objectivity of thisconceptual construction depends entirely on the method ofpoint-coincidences. Any features of the world-picture which do notcontribute to the systematization of point-coincidences are notphysically objective. And all world-pictures which contain lawsgoverning point-coincidences are thoroughly equivalent. Furthermore, since any functional, single-valued deformation of theworld-picture leaves all point-coincidences undisturbed, the equationsof physics retain their form under such transformations, implying thatthey are covariant under all substitutions. These substitutionsalso leave the form of physical equations unchanged forcoordinate-systems in motion, allowing for the relativity of spacewithin such coordinate-systems, thus depriving space and time of the“last vestige of physical objectivity” (Schlick2006a, Sec. VII).

Einstein was so impressed with Schlick’s presentation that, ina letter to Arnold Sommerfeld, Einstein described it as“masterly”, perhaps because Schlick was one of the firstcommentators to see that space and time have no existence or realityprior to the metric field.

Nor was it long beforeSpace and Time … was succeededby the first edition of Schlick’sGeneral Theory ofKnowledge. During the same period, Schlick spent a yearengaged in war work at Aldershof airport outside Berlin followed, in1921, by an appointment at Kiel. Since rumors were alreadyspreading about a possible appointment at Vienna, Schlick’sfamily stayed in Rostock until 1922, when they moved to Vienna where heassumed the Chair ofNaturphilosophie which had previouslybeen occupied by Ernst Mach and Ludwig Boltzmann (v. d.Velde-Schlick 2008; Ferrari 2009). Schlick’s selection forthe post was probably initiated by the mathematician Hans Hahn and thephysicist Phillip Frank, with a strong recommendation fromEinstein. When Schlick arrived in Vienna, he immediately becameinvolved with Hahn and Frank, as well as the economist Otto Neurath, intheir Thursday night discussion meetings in the Chemistry Building ofthe University of Vienna. Schlick was a welcome addition to thegroup, and together they formed the core of what would later becomeknown as ‘the Vienna Circle’ (Uebel 2003). Philosophywould never be the same.

However, before arriving in Vienna, Schlick engaged theneo-Kantians,Hans ReichenbachandErnst Cassirer,who had published their own philosophical understandingsof the new physics of Relativity. In hisRelativity Theoryand Apriori Knowledge of 1920, Reichenbach had argued for amodified conception of Kant’s syntheticapriori, whichchallenged Schlick’s thought in a decisive way(Reichenbach 1920). At Einstein’s request, Schlick wrote toReichenbach in the Fall of 1920, hoping to air the differences betweenthem (Schlick 1920; Einstein 1920). In his own essays, Schlick hadchallenged Kantian apriorism principally by identifying thepresuppositions of the new physics as conventions, inPoincaré’s sense. Since the presuppositions ofRelativity were alien to classical physics, they were nothing like theself-evident, eternal verities that comprised the Kantianapriori. But while Schlick rejected Kant’s treatment oftheapriori altogether, Reichenbach claimed to have preservedits most important element, its constitutive function (Reichenbach1920, Ch. V; Friedman 1999, 59–70; Oberdan 2009). For Kant hadattributed theapriori the far more philosophicallysignificant function of constituting the object of experience orknowledge. Indeed, such principles are the general laws for orderingexperience to produce knowledge. Since all empirical knowledgepresupposes these ordering principles, they can never conflict withexperience and are, in this sense, necessarily true. (Reichenbach1920, pp. 55–56) Schlick first wrote Reichenbach in the Fall of1920, acknowledging that he regarded the assumption of constitutiveprinciples as self-evident; indeed, he feared that the matter was soobvious that he might not have discussed it sufficiently inhisGeneral Theory of Knowledge (Schlick 1920a, p. 1; Oberdan1994, pp. 109–110). Nonetheless, it is precisely the principleswhich Reichenbach himself had identified as syntheticapriori that constitute an observation or measurement of anexperience. Yet, Schlick confessed, he was unable to discoverany characteristics of these alleged syntheticaprioriprinciples that genuinely distinguish them from conventions. Ofcourse, it then follows that the precepts Reichenbach called“syntheticapriori” were just what Schlick hadidentified as “conventions” and the differences betweenthem were, at most, terminological (Schlick 1920b, 2). But thisapparently terminological difference, Schlick thought, masked a fardeeper difference separating them since, on Reichenbach’sunderstanding, theapriori constitutes the objects ofexperience and knowledge whereas, on Schlick’s, conventions onlyconstitute concepts, which may be applied to experiences and objects,but do not constitute them. Thus Schlick insisted ondistinguishing his own realist epistemology from Reichenbach’smodified Kantianism, because of the latter’s implicitanti-realism.

Schlick also contributed a critical essay on Ernst Cassirer’s1921 work onEinstein’s Theory of Relativity to theprestigious journalKant-Studien (Cassirer 1921; Schlick1979a, 322–334). In “Critical or Empiricist Interpretationof Modern Physics?” of 1921, Schlick explained thatCassirer’s argument rested on a false dichotomy. On the onehand, Cassirer’s own Logical Idealism incorporates principles forthe ordering and measuring of sensations to constitute physicalobjects. On the other hand, the only alternative Cassirerconsidered is a variety of phenomenalistic empiricism founded on“thesensualistic concept of experience”. Inother words, Cassirer’s operative assumption is simply that theonly possible philosophical frameworks for understanding contemporaryscience are a strict empiricism or one incorporating constitutiveprinciples. Of course, Schlick regarded his own philosophicalframework as a clear counterexample, since it is an empiricistepistemology distinguished by its inclusion of constitutiveprinciples. Thus, Cassirer committed the same error asReichenbach by blithely ignoring the possibility of constitutiveprinciples which are not syntheticapriori judgments. Naturally, a combination of empiricism with constitutiveprinciples would fall somewhere between the strict empiricism Cassirerrefutes and the Logical Idealism Cassirer defends. At this point,Schlick first used what would eventually become a familiar complaintagainst Kant and the neo-Kantians among Logical Positivists, especiallytheir characterization of the constitutive principles as syntheticjudgmentsapriori. As Schlick understood constitutiveprinciples, they are certainly not syntheticaprioriprinciples, for they are conventions, which are neitherapriori nor synthetic (Schlick 1979a, 322–334). Theresult of Schlick’s critique was, in Einstein’s words,“truly inspirational” (Einstein 1921).

7. Transition

Shortly after Schlick arrived in Vienna, he was invited by themathematician Hans Hahn to participate in a seminar onPrincipiaMathematica by Alfred North Whitehead and Bertrand Russell. Uponits conclusion, Schlick organized (at the request of his students,Herbert Feigl and Friedrich Waismann) organized an extra-curriculardiscussion group, which came to be called the ‘SchlickCircle’ and (eventually) the ‘Vienna Circle’. Theirfirst reading wasTractatus Logico-Philosophicus, written by Russell’sstudent, Ludwig Wittgenstein (Wittgenstein 1961; Stadler 2001, Ch.5). Soon, Schlick was writing Wittgenstein, seeking additionalcopies of his work, telling him about the study group in Vienna, andrequesting personal meetings. After several failed attempts, Schlickfinally arranged with Wittgenstein’s sister, MargareteWittgenstein Stonborough, to visit him in early 1927 (McGuinness 1967,14). The first clear evidence that Schlick had (at last!) obtaineda copy of the Tractatus was in a letter to Einstein in June of 1927.(Schlick 1927a) The following month, Schlick effusively describedtheTractatus as “the deepest” work of the newphilosophy (Schlick 1927b). Over the next few years, Schlick andWittgenstein met as time permitted, carrying on philosophicaldiscussions ranging over a broad array of topics, from the idea ofgeometry as syntax, to verificationist and operationalist theories ofmeaning, topics in logic and mathematics, and even solipsism.

Of course, thediscussions of verifiability in the late 1920s led to widespreaddisputes in later positivist thought. But even in the early years,Schlick and his students to wondered how ethical statements might beverifiable. InProblems of Ethics, Schlick attempted tointerpret ethical statements as empirical claims about the means formaximizing happiness. Relying on relative judgments of values, Schlickargued that an empirical foundation of an ethical system based onmaximum happiness. On Schlick’s account, happiness is not to beconstrued superficially but as the elated sense of fulfillment thataccompanies actions carried out for their own sake. Hence, there are noapriori moral statements fixing absolute moral values.

Wittgenstein dictated some of his thoughts to Schlick, including astrident verificationist series of remarks, and shared severalmanuscripts with Schlick as well, including (perhaps) his so-called‘Big Typescript’ of 1932–1933 (Iven 2009,Wittgenstein 2005). Several other documents survive the period,particularly notes taken by Schlick’s student, FriedrichWaismann, when he accompanied Schlick on his visits to Wittgenstein(McGuinness 1967). In addition, there were joint travels undertaken byWittgenstein and Schlick during the period of their interaction (Iven2009; Stadler 2001, Ch. 6). The principal effect of this influence onSchlick was the assimilation, into his already well-definedphilosophical views, of insights stimulated by theseconversations.

During the sameperiod, Rudolf Carnap joined the faculty of the University of Vienna aswell as the Schlick Zirkel. He brought a manuscript with him,which he called “Konstitutionstheorie”, and which waseventually published, with Schlick’s help, as The LogicalStructure of the World (Carnap 1928). Schlick even assistedCarnap in locating a publisher for the work. It was at this timethat Schlick penned the essay “Experience, Cognition, andMetaphysics” of 1926, which represents a particularly importantjuncture in his thinking. Schlick attempted to link currentinfluences on his thought – Wittgenstein’s Tractatus and Carnap’s Aufbau – with his earlier ideas, especially thedistinction between intuitions and concepts (Schlick 2008, pp. 33–56;Wittgenstein 1961; Carnap 1928; Schlick 2009, Sec. 7).

Within a few years, Schlick wrote the essays which are characteristicof his early Positivist thought. The first one, “The TurningPoint in Philosophy,” appeared in 1930. It contains an earlyversion of the thesis that the function of philosophy is the analysisof meaning (Schlick 1979b, 154–160). A more decisive article was the1932 essay, “Positivism and Realism”, a classic piecewhich shaped some of the most characteristic philosophical work toemerge from the Positivist tradition (Schlick 1979b, 259–284). Schlickinterprets the verifiability principle strictly, by spelling outverification in terms of sensible experience, but at the same timebroadly, construed to admit any logically conceivable circumstances ofverification (like the future verification of mountains on the farside of the moon). The basis of this principle, Schlick argues, is tobe found in scientific practice. He cites Einstein’s analysis of“simultaneity” in Special Relativity as his primaryexample, an illustration which would become a staple of Positivistlore. Schlick also mentioned Planck, who acknowledged that experiencewas the source of scientific knowledge. Schlick called thephilosophical view founded on this principle, “LogicalPositivism”, using the designation introduced by A. E. Blumbergand Herbert Feigl (Blumberg and Feigl, 1931). As Schlick explained it,Logical Positivism is essentially a realist epistemology, like the onedeveloped in Schlick’s General Theory of Knowledge, which shareslittle with the classical positivism ofAuguste Comte,Ernst Mach,and Hans Vaihinger. Schlick’s principal conclusion was thatLogical Positivism never denies the reality of material objects but,rather, equates physical reality with the lawfulness ofexperience. Unfortunately, Planck, who had always supportedSchlick in the past, misunderstood the essay, interpreting it as apolemic for Machian positivism, and harshly condemning it (Planck1932).

8. The Protocol Sentence Controversy

The celebrated ‘protocol sentence controversy’ in theVienna Circle was initiated by Carnap’s syntactic analysis ofobservation sentences, or ‘protocols’ (Carnap 1932a). Thesalient feature of Carnap’s analysis was its‘syntacticism’, the idea that meaning is wholly a functionof the serial arrangements of symbols. Naturally, syntacticismprecludes any effort to explain protocols by their relation to‘experiences’, ‘sensory impressions’, or‘observations’. Otto Neurath criticized Carnap’sanalysis, arguing that protocols should be understoodphysicalistically, as sentences of the physical language, and theirorigins and grounds are to be explicated naturalistically, by means ofbehaviorist psychology (Uebel 2007, Ch. 8). But Schlick recoiled atthe very idea that the relation between observation sentences and whatthey describe should be explicated by any means other thanphilosophical analysis. So, in his classic 1934 essay, “On theFoundations of Knowledge,” he introduced so-called‘affirmations’ (Konstatierungen) in the effort toexplicate the relation between physicalistic protocols and theexperiences on which they are grounded (Schlick 1979b, 370–387).Otto Neurath responded, in his 1934 essay “Radical Physicalismand the ‘Real World’”, condemning Schlick’sview as just so much metaphysics, while Carnap regarded affirmationsas protocols of a phenomenal language, along the lines of one of thealternatives he had outlined in his 1932 paper, “On ProtocolSentences” (Neurath 1983, 66; Carnap 1932b, 458–463). Still,Carnap objected that, unless Schlick could explain how affirmationsmight be translated into sentences of the physical language, thenaffirmations violated the thesis of physicalism. Schlick respondedthat affirmations, like “Here now white”, were theresponses of investigators when asked about their personal experiencesin experimental situations. Thus construed, the demonstrativecharacter of affirmations ensures their incorrigibility (Schlick 2009,661–674). Although their demonstrative character prevents themfrom being regarded as proper physicalistic sentences, they areobviously translatable into statements of the physical language. Butthen, even though they lose their distinctive epistemic character, forthey are no longer incorrigible or indubitable, they still conveyepistemic warrant to their physicalistic translations.

To Carnap, the deeper problem was that, by the lights of his 1934 workonThe Logical Syntax of Language, affirmations are notwell-formed expressions at all. Earlier, in his (1932a) contributionto the protocol sentence controversy, Carnap’s treatment ofobservation was based on the Thesis of Metalogic, the idea that allphilosophical contentions (which are not nonsense) are metalinguisticclaims about linguistic expressions and their logical (particularlysyntactical) properties (Carnap 1932a, 435n). The function of theMetalogic Thesis was to isolate pseudo-theses or statements which seemto concern substantive matters but are really concerned with logicalor linguistic matters. Of course, these pseudo-theses became known as‘pseudo-object sentences’ and their analysis became acenterpiece of Carnap’sLogical Syntax-era philosophy (Carnap1937, Sec. 74). And the Metalogic Thesis, together with the Principleof Tolerance (which asserts that the choice of any specific languageis a conventional decision), formed the principal theses of Carnap’sphilosophy of logic in the Thirties (Carnap 1937, 51–2). OttoNeurath, who endorsed the Metalogic Thesis and the TolerancePrinciple, drew the obvious conclusion that Schlick’s defense of thecorrespondence conception of truth, explicated by his analysis ofaffirmations, committed him to the recognition of “the one, truereality” and “the real world” (Neurath 1983,pp. 106–8; Uebel 2007, Sec. 8.2). In short, Schlick’sfoundations were spelled out in nothing more than philosophicalpseudo-statements.

What Neurath and (presumably) Carnap both missed was thatSchlick’s thinking about meaning and linguistic significance hadcome a long way since his 1926 essay on “Experience, Cognition,and Metaphysics”, in which he tried to link Wittgenstein’sremarks about internal relations in theTractatus with his owndoctrine of implicit definition (Wittgenstein 1921, 4.122, 4.125,4.1251, 5.232). There the goal was to apply both these ideas to thedistinction between intuitions and concepts. The result wassomething of a disaster. For it implied what Schlick called“The Incommunicability of Contents”, the idea that anyeffort to communicate non-formal contents, like the greenness of thecolor green or the distinctive smell of wood smoke, must forever remainineffable (Oberdan 1996, Sec. 2). But it was not long beforeSchlick’s efforts to explain linguistic meaning and scientificknowledge in terms of their ‘form’ and‘content’ were abandoned and by the 1934–1935 academicyear, he was developing what might well be called ‘a semanticconception’, spelled out in terms of grammars and the rules whichconstitute them, and presenting his new vision of language in hislectures on “Logik und Erkenntnistheorie”(Schlick 1934–5).

9. Grammar and Meaning

In “Logik und Erkenntnistheorie,” Schlick thoughtthe most important component of languages are grammatical rules, whichare of two kinds. First of all, there are ‘internalrules’, which govern the use of expressions in relation to otherexpressions, much like the formation and transformation rules of formallogic. In addition, Schlick conceived of a second type ofgrammatical rule, which he called ‘application-rules’(Anwendungsregeln), regulating the use of expressions inconnection with, or application to, observable extra-linguisticsituations. Of course, application-rules govern not onlydescriptions of observable situations, but the use of indexicals anddemonstratives as well, thus legitimizing Schlick’s affirmationsby grounding them in grammar. And Schlick conceived grammar withsufficient breadth to encompass the natural languages of everyday lifeas well as the technical and highly regimented languages ofscience. Concurring with Carnap’s Principle of Tolerance,Schlick regarded the choice of grammatical rules, the choice of aparticular grammar rather than an alternative, as conventional andtherefore independent of extra-linguistic matters. And hisendorsement of grammatical conventionalism was specifically intended toaccommodate choices between languages which differed radically, asdemonstrated in his treatment of philosophical pseudo-problems(Oberdan 1996, Sec. 3).

Schlick presented his latest conception of grammar as well as itsapplication to philosophical pseudo-problems in his 1936 essay on“Meaning and Verification” (Schlick 1979b,456–481). In particular, he demonstrated that the criterion ofverifiability is rooted in grammar and concerns any grammaticallywell-formed proposition which is neither analytic norcontradictory. He reiterated his conception of grammar as thecollection of rules governing the formation and use of meaningfulexpressions, including the rules governing the use of language inconnection with experience, rules which are introduced by acts ofostension (Schlick 1979b, 464–7). Although the result is ananalysis of language which provides a powerful treatment of many‘typical’ metaphysical theses, like Platonism,psychologism, and phenomenalism, in “Meaning andVerification” Schlick demonstrated its utility by applying it tosolipsism. The upshot is that solipsism is a contingent truth which istreated by its defenders as unfalsifiable. But statements which areinsulated from the possibility of falsification are object-language‘mis-expressions’ of what are, at bottom, grammaticalrules. The parallel with Carnap’s analysis of pseudo-object sentencesas metalinguistic assertions rather than ‘real-object’sentences could not be more striking. And just as Carnap regarded theformal mode translations of philosophical theses as proposals to adopta certain language form, Schlick contended that the solipsist’s thesiswas not abona fide contingent claim but simply an attempt tointroduce a particular mode of speech. Thus, by the time of“Meaning and Verification”, he had moved well beyond his‘Form and Content’ stage, modulating the virulentPositivism of his earlier thinking, to arrive at a more mature andbalanced conception of the issues at the focus of his philosophicalconcerns (Oberdan 1996, Sec. 5).

10. Death

As Schlick was leaving class on June 22, 1936, he was shot four timesin the legs and abdomen by Johann Nelböck, a former philosophystudent who had been threatening Schlick for several years. In fact,Nelböck had been confined in an asylum for observation anddiagnosed as a paranoid schizophrenic. Eventually, other factors–both social and political- emerged which may also haveinfluenced Nelböck. The number of possible motivations make itnearly impossible to fully understand what was in Nelböck’s mindat the time of his murderous actions. But the result of his misdeedis clear: with the death of Moritz Schlick, philosophy lost one of itsmost creative thinkers. See Stadler 2001 (Part 2, Sec. 3–3.2) for acomprehensive account of Schlick’s death.

Bibliography

Primary Literature

Note: The publication of the entire corpus ofSchlick’s writings is appearing under the titleMoritzSchlick Gesamtausgabe (Vienna: Springer), under the generaleditorship of Friedrich Stadler (Vienna) and Hans Jürgen Wendel(Rostock). The volumes which have appeared (Schlick 2006a, 2006b, 2008,2009, and 2012) have already established new editorial standards forthe eventual publication of the works of all the major figures of earlyLogical Positivism. At the same time, through the dedication of asmall group of editors under the leadership of Stadler and Wendel, theSchlick collection is far more advanced than the collections of otherearly Positivists, which are also currently under way.

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