Aristotle is properly recognized as the originator of the scientificstudy of life. This is true despite the fact that many earlier Greeknatural philosophers occasionally speculated on the origins of livingthings and much of the Hippocratic medical corpus, which was writtenbefore or during Aristotle’s lifetime, displays a seriousinterest in human anatomy, physiology and pathology. And Plato hasTimaeus, in the eponymous dialogue, devote a considerable part of hisspeech to the human body and its functions (and malfunctions).Nevertheless, before Aristotle, only a few of the Hippocratictreatises are both systematic and empirical, and their focus is almostexclusively on human health and disease.

By contrast, Aristotle considered the investigation of living things,and especially animals, central to the theoretical study of nature.Constituting roughly 25% of the extant corpus, his zoological writingsprovide a theoretical defense of the propermethod forbiological investigation; and they provide a record of the firstsystematic and comprehensive study of animals. There was nothing ofsimilar scope and sophistication again until the 16^thcentury. In the nineteenth century the great anatomist Richard Owenintroduced a two lecture survey of Aristotle’s zoologicalstudies by declaring that “Zoological Science sprang from his[Aristotle’s] labours, we may almost say, like Minerva from theHead of Jove, in a state of noble and splendid maturity” (Owen1992, 91). Before examining this remarkable achievement, a few wordsabout its creator are in order.^[1].

• 1. Life and Work
• 2. Aristotle’s Philosophy of Science
• 3. Caveat lector
• 4. Philosophy of Biology
• 5. Aristotle’s Biological Practice
  • 5.1 TheHistory of Animals as a Report of the results of aHoti-Investigation
  • 5.2 From Inquiry to Understanding; fromhoti todioti.
• 6. A Concluding Puzzle
• Bibliography
  • Selected Texts, Translations, Commentaries
  • Secondary Sources on Aristotle’s Biology
• Academic Tools
• Other Internet Resources
• Related Entries

1. Life and Work

Aristotle was born in Stagira on the northern Aegean coast in 384BCE.His father Nicomachus was physician to King Amyntas III of Macedon,and his mother was of a wealthy family from the island of Euboea. Hewas sent at the age of 17 to Athens, where he studied in Plato’sAcademy for 20 years, until Plato’s death in 347. By then he haddeveloped his own distinctive philosophical ideas, including hispassion for the study of nature. He joined a philosophical circle inAssos on the coast of Asia Minor, but soon moved to the nearby islandof Lesbos where he met Theophrastus, a young man with similarinterests in natural science. Between the two of them they originatedthe science of biology, Aristotle carrying out a systematicinvestigation of animals, Theophrastus doing the same for plants.

In 343 Aristotle was asked by Philip II of Macedon to tutor his sonAlexander. By 335 he had returned to Athens, now under the control ofhis former student Alexander. With Theophrastus he founded a‘school’ in a public sanctuary known as the Lyceum. Heheaded the Lyceum until the death of Alexander the Great in 323. Withanti-Macedonian feelings running high in Athens, Aristotle retired tohis mother’s birthplace. He died there in 322BCE.

The surviving corpus of Aristotle derives from medieval manuscriptsbased on a 1^st century BCE edition. There were nocommentaries on the biological works written until they werecollectively translated into Arabic. The first appearance ofAristotle’s biological writings in the West are Latintranslations, by Michael Scot, of an Arabic edition, which forms thebasis of Albertus Magnus’De animalibus. In the13^th century, William of Moerbeke produced a Latintranslation directly from the Greek. The first printed editions andtranslations date to the late 15^th century, the most widelycirculated being that of Theodorus Gaza. In addition to the threeworks traditionally referred to asHistory of Animals(HA),Parts of Animals (PA) andGeneration of Animals (GA), there are a number ofbriefer ‘essays’ on more specialized topics:On animalmotion,On animal locomotion,On respiration,On life and death,On youth and old age,Onlength and shortness of life,On sleeping and waking,On the senses and their objects (the last six being includedin the so-calledParva naturalia). Whether one shouldconsiderDe Anima (On the soul) part of this projector not is a difficult question. What is certainly clear, however, isthat there are important connections between the theoretical approachto the relationship between body and soul defended in that work andthe distinctive way that Aristotle approaches the investigation ofanimals.

In order to understand Aristotle’s distinctive approach to thestudy of living things, it is imperative to situate it within hisnatural philosophy and his philosophy of science. The first book ofAristotle’sParts of Animals is, in fact, largelydevoted to doing just that, and after a brief discussion ofAristotle’s general views about scientific inquiry andexplanation, we will turn to it.

2. Aristotle’s Philosophy of Science

In sections 4, 5 and 6, we will explore the ways in which Aristotlesystematically organizes and explains an extraordinary body ofinformation about animal anatomy, physiology and development. ButAristotle was able to accomplish what he did in zoology because he hadgiven a great deal of thought to the nature of scientific inquiry. Howdoes one progress from the superficial and unorganized state ofeveryday experience toward organized scientific knowledge? To answerthis question, you need a concept of the goal to be achieved, andAristotle developed such a concept in hisPrior andPosterior Analytics (henceforth abbreviated asAPr.andAPo., respectively). The goal of scientific inquiry, heargued, was a system of concepts and propositions organizedhierarchically, ultimately resting on knowledge of the essentialnatures of the objects of study and certain other necessary firstprinciples. These definitions and principles form the basis of causalexplanations of all the other universal truths within the domain ofstudy. Those other universal truths should identify attributesbelonging to a subjectper se, in virtue of thatsubject’s nature. The example he uses when he introduces hisaccount of scientific demonstration to illustrate such propositions isfrom geometry: having interior angles equal to two right anglesbelongs to all and only triangles in virtue of their being triangles(APo. I 4, 5). This attribute belongs to allequilateral triangles as well—not, however, becausethey are equilateral, butbecause they are triangles. Thusscientific knowledge of such a proposition, knowledge that displaysthe reason why any triangle has this property, must explain why thisproperty belongs to trianglesas such. The explanation, ofcourse, will appeal to the essential character of three-sidedrectilinear plane figures, i.e. to what it is to be a triangle.

The second book of thePosterior Analytics discusseshow to achieve this goal of scientific knowledge, one centralconcern being how knowledge of essences, expressed in definitions, isrelated to explanations expressed in the form of causaldemonstrations. Plato had formulated a famous paradox of inquiry inhis dialogueMeno: either you know the object of yourinquiry, in which case inquiry is unnecessary; or you don’t knowthe object of your inquiry, in which case inquiry is impossible(Meno 80d5–e5). Aristotle reminds us of this paradox in thefirst chapter of thePosterior Analytics, but his fullsolution only emerges in book II. There, he argues that perceptualexperience gives us a grasp of the target of inquiry that, though itdoes not count as scientific knowledge, does serve to direct furtherinquiry. He begins the discussion by presenting us with a claim abouthow objects of inquiry are linked to objects of scientificknowledge.

The things about which we inquire are equal in number to the things weknow scientifically. We inquire about four things:the fact,the reason why,if something is,what somethingis. (APo. II 1, 89b23–25)

Aristotle conceives of these four inquiries aspaired, andthere is a naturalsequence in each pair. Knowing that somestate of affairs is the case, we can inquire into the reason why it isthe case.

When we knowthe fact we inquire aboutthe reasonwhy (e.g., knowingthat it is eclipsed orthatthe earth moves, we inquire intothe reason why it iseclipsed orwhy the earth moves). (APo. II 1,89b29–31)

Similarly, if we conclude an inquiry into whether something exists, wecan go on to investigate its nature, what it is.

And having come to knowthat it is, we inquirewhatit is (e.g.: Then what is a god? Or what is a man?). (APo. II1, 89b34–35)

The examples reveal a distinction that structures much of thediscussion for the next ten chapters. For it looks as if‘factual’ inquiries concern whether some attribute belongsto some subject (movement to the earth, eclipse to the moon), and thesearch for the reason why will be a search for the causal explanationof the attribute belonging to that subject. By contrast, it looks likethe move from ‘if’ to ‘what’ is a move fromestablishing the existence of some subject (‘god’,‘man’) to establishing what it is.

However, the distinction is not, it turns out, so clear-cut. Havingbegun to illustrate the distinction between inquiryif orwhether something is andwhat it is with thequestion ‘whether there is or is not a centaur or a god’,he then characterizes the knowledge achieved as ‘knowingthat it is’. And in the second chapter, he begins tolink the two sequences of inquiry by means of his syllogistic conceptof “middle term,” the term that is common to the twopremises in a syllogistic proof.

Thus it results that inall our research we seek eitherif there is a middle term or what the middle term is. For themiddle term is the cause, and this isin every case what issought. (APo. II 2, 90a7–9)

That is, in any valid syllogistic inference, the middle term shared bythe premises is the warrant for the conclusion. In scientificexplanation, however, the middle term mustalso identify thecause of the fact given in the conclusion—what that termidentifies is the causal link between the subject and attribute. Touse another of his common examples, if we seek to explain the periodicsound of noise in the clouds, the middle term must identify the causeof the connection between that noise and those clouds. Moreover, onAristotle’s account of the relationship between causaldemonstration and scientific definition, knowing thecause ofthunder is at the same time knowing theessence of thunder,what thunder really is.

There is a difference between saying why it thunders and what thunderis. In the one case you will say: Because the fire is extinguished inthe clouds. But: What is thunder?—A noise of fire beingextinguished in the clouds. Hence the same account is given indifferent ways: in one way it is a continuous demonstration, in theother a definition. (APo. II 10, 94a4–8)

In theAPo., Aristotle returns regularly to such standardexamples of natural phenomena as thunder and eclipses—but healso, and importantly, provides an extended biological example, theseasonal loss of leaves in broad-leafed plants.^[2] In ch. 16, Aristotle imagines an inquiry that begins with questionssuch as ‘Why do fig trees and grape vines lose theirleaves?’. The model answer is ‘Because they are bothbroad-leafed.’ That is, the inquiry seeks some other feature,common to both kinds, related to the target of inquiry, theseasonal loss of leaves. The ‘because’ is, however,preliminary—it is best to see being broad-leafed as a steptoward causal explanation. Chapter 17 picks up the example, in thecontext of arguing that basic scientific inquiry seeks, whereverpossible,co-extensive predications, which those between leafloss and fig trees, or leaf loss and grape vines, are not. Thecandidate major premise, however—‘Whatever is broad-leafedloses its leaves’—does identify a co-extensiverelationship between subject and predicate. It may thus serve as aproper scientificexplanandum, and ‘broad-leafed’can serve to identify a kind, all and only the members of which losetheir leaves.^[3] Thus, the middle term of the preliminary explanation becomes thesubject of a more basic, co-extensive predication. The causeof broad-leafed trees losing their leaves will, then, be somethingmore fundamental about broad-leafed trees, here identified as thesolidification of moisture at the leaf juncture, which can thus serveas the middle term in a causal explanation of this fact. But it willalso serve as part of a definition of leaf loss.

The middle is the account of the first major term [i.e. the predicatein the conclusion], for which reason all the sciences come aboutthrough definition. (APo. II 17, 99a22–23)

That is, we will have, if our research goes well, an account of whatloss of leaves is. Along the way a process of identifying the kind,all and only the members of which will lose their leaves due to sapcoagulation, is assumed. Yet theAnalytics provides nosystematic discussion about whether there are general criteria foridentifying these basic scientific kinds. As we will see, this is thetopic of one of the most interesting sections ofOn the Parts ofAnimals, book I.

There are two quite different questions we need to ask about how theseideas about inquiry and explanation in theAnalytics arerelated to Aristotle’s investigations of animals: first, how isthephilosophy of biology presented inPA I relatedto the general account of explanation, definition and inquiry in thePosterior Analytics^[4]; and second, to what extent do the treatises reporting his actualinvestigations of animals conform either to his general account ofscientific knowledge and inquiry inAPo., or to the normsregarding the study of animals laid down inPA I. Theremainder of this entry will be organized around these twoquestions.

3. Caveat lector

First some preliminary remarks are in order about what weare—and are not—discussing. It seems obvious, once stated,that the actual activity of studying animals is different from theactivity of writing or teaching about animals based on that study. Wehave access to a number of Aristotle’s systematically organizedwritings on animals; we donot have direct access to hisactual investigations. Some authors studied by historians of sciencediscuss, in their written work, the methods they used to gather theinformation and work out their theoretical ideas and even provide‘diaries’ describing their day-to-daystudies—Aristotle is not one of them. Nor did anyone else reportobserving Aristotle carrying out his studies. There are reasonableinferences we can make from his writings; for example that heconsulted with bee-keepers, fishermen and sponge divers, that he (orsomeone under his guidance) performed a great many dissections on awide variety of animals, that there were at least some diagramsproduced based on these dissections, and so on. Moreover, on thequestion of how he reasonedto specific explanations we canmake some reasonable inferences from things he says about propermethods of biological inquiry. But it is important to keep in mindthat we are studying texts that present, in a highly structured andtheoretical manner, theresults of an actual investigation,the details of which we know very little.

It is also unclear what is the intent of the texts wedo havethat report on these investigations. It is sometimes said they are‘lecture notes’. That seems pretty clearly wrong; they aretoo carefully written and structured. But it does seem clear, fromcross-references, that some of them were to be studied in a certainorder, and this ordermay conform to a course of study in theLyceum. Interestingly, while all of the other biological treatisesrefer for further information to ‘the animalinquiries’,that is to something like theHistory ofAnimals that has come down to us, often in conjunction with‘the dissections’, ourHistory of Animals has noreferences to the other, explanatory studies. This suggests that the‘inquiries and dissections’ had a different function insuch a course of study, perhaps something akin to ‘referenceworks’.

Finally, it is also worth recalling that the series of treatises wehave was likely compiled hundreds of years after Aristotle’sdeath from whatever he left. It seems unlikely we will ever be able todetermine the exact relationship between the so-called‘Andronican’ edition, the likely source of our texts, andwhat was produced during Aristotle’s lifetime.

These three caveats place constraints on what I can reasonably claimto be doing. I will be discussing the treatises that report theresults of Aristotle’s investigations of animals. I will assumethat the texts that have been passed down to us reflect what he wroteon this subject, and that the cross-references in those texts are hisand reflect his own views about how these various studies are relatedto each other.

4. Philosophy of Biology

On the Parts of Animals, book I (PA I) begins byoutlining its purpose, which is to establish a set of standards forjudging natural investigations (639a15). Its five chapters pursue thispurpose, discussing the appropriate level of generality for suchstudies, the modes of causality and of necessity to be used inbiological explanations, the relation of form to matter in livingthings, the proper method of logical division for this subject matter,the means of identifying kinds and their activities at the properlevel of abstraction, and much more. Two sorts of evidence support theconclusion that this book is intended to deal with problems andquestions that arise in the application of Aristotle’s generalphilosophy of science, found in thePosterior Analytics, tohis theoretical investigation of living nature.

The first kind of evidence consists of passages introducing hisbiological investigations that appear to make explicit reference tothe account of scientific knowledge inAPo. The followingpassage from theHistory of Animals (a better though lessfamiliar translation would beAnimal Inquiries), for example,suggests that the entire biological project is organized in accordancewith the theory of inquiry developed inAPo. II. This passagecomes near the end of chapter six in the first book ofHA.After five chapters in which Aristotle lays out the kinds ofsimilarities and differences among animals to be studied and sketchesthe ways in which they are to be investigated, he makes the followingprogrammatic statement about the investigation to come, and where itfits in the entire scientific study of animals.

These things, then, have now been said by way of outline to provide ataste of what things need to be studied, and what it is about themthat needs to be studied, in order that we may first grasp thedifferences and the attributes belonging to all animals. After we dothis, we must attempt to discover the causes. For it is natural tocarry out the investigation in this way, beginning with the inquiryinto each thing; for from these inquiries it becomes clear both aboutwhich things (peri hôn) the demonstration(tên apodeixin) should be and from which things(exhôn) it should proceed. (HA I 6,491a7–14)

The natural way to proceed, then, is to begin with inquiry(historia), with the aim of grasping the differences between,and attributes of, all the animals; andthen to attempt todiscover their causes. This is natural because, given that our goal isdemonstrative understanding, we want to end up with a cleardistinction between the facts to be explained (theperihôn) and their explanation (theexhôn). This statement echoes the summary, inAPo. I 10, of the components of demonstrative knowledge:

Nevertheless there are by nature these three [components ofdemonstrative knowledge]: that about which (peri ho) itproves, what it proves, and those things from which (exhôn) it proves. (76b21–22)

TheHistory of Animals characterizes itself as establishingthe attributes and the differences that belong to all animals, andclaims that by carrying out this inquiry we are prepared to go on tosearch for the causes. Indeed, he appears to suggest that a successfulhistoria or factual inquiry will prepare us to grasp thedifference between those facts that need to be explained and thosethat will be invoked in our explanations. In the language of thePosterior Analytics:HA establishes thefact, e.g.that all animals with lungs havewindpipes, orthat all cetacea have lungs and are viviparous,typically seeking to identify groups by means of discoveringco-extensive differentiae with the aid of the method of division.^[5] The proper use of division, moreover, will give clear indications ofwhich predications are basic and which derivative. Works such asParts of Animals orGeneration of Animals, on theother hand, seek to establish the reason why—the cause—ofthe fact. If Aristotle is following the method described in theAnalytics, these causal explanations should at the same timepoint us to essential definitions of what it is to be a windpipe or tobe viviparous. It is a question currently much debated whetherdefinition was, in fact, an explicit goal ofHA or simply aconsequence of the explanatory goal clearly identified in the abovepassage fromHA I 6; and if so, whether definitions of animalkinds were sought, or only definitions of their attributes.As we will see, there are a number of chapter summaries in theexplanatory treatises that make a point of claiming thatbothan explanation ofwhy a part is found in those animals thathave it,and an account ofwhat that part is, havebeen provided; but one must work very hard to reconstruct anydefinitions of animal kinds in those treatises.^[6]

A number of texts in Aristotle’s causal investigations reinforcethe message ofHA I 6, stressing that the preliminary work ofinquiries that establish and organize the facts at various levels ofgenerality has been accomplished; and they regularly refer tosomething like what is reported in ourHA as the place tolook for the results of this preliminary work. Two explicit statementsto that effect follow, one from the beginning of his study of thecauses of the differences in animal locomotion, one from the beginningof his study of the causes of the differences among the parts ofanimals.

Clearly there needs to be a study of all of these questions aboutanimal locomotion and any others of the same kind; forthat(hoti) these things are thus is clear from our inquiries intonature (tês historias tês phusikês);the reason why (dioti) must now be investigated.(IA 1, 704b7–10)

From which parts and from how many parts each of the animals isconstituted has been exhibited more clearly in the inquiries aboutthem (en tais historiais tais peri autôn); it is thecauses owing to which each animal has this character thatmust now be examined, on their own and apart (chorisantaskath’hauta) from what was said in the inquiries.(PA II 1, 646a8–12)

Each of these passages explicitly describes the study of animals withwhich Aristotle is engaged in the language of Aristotle’s theoryof research inAPo. II 1. Indeed, the passage fromHA I 6 does so by insisting that thenaturalmethod to use is to first get clear on the differences andattributes to be demonstrated (‘establish the factthat…’) before going on to find the causes(‘the reason why, i.e. the cause’) to be appealed to inthese demonstrations. Animal inquiries (historiai) are a kindofhoti inquiry—that is, theHistory ofAnimals presents the facts to be explained, organized so as to beprepared for causal demonstration.^[7]

TheIA andPA, on the other hand, refer tothemselves as pursuing a causal inquiry intothe reasonwhy the various kinds of animals are differentiated as theyare, and they acknowledge that they are able to do this preciselybecause the factual investigation into the locomotion and parts ofanimals has been accomplished. In both cases Aristotle emphasizes thedistinction on which we are focused, perhaps in order to remind hisreaders of his philosophy of scientific research.

There is a second line of evidence, quite independent of theseprogrammatic statements, which leads to the same conclusion. Thetopics covered inPA I take the form of specifications of thecentral topics of thePosterior Analytics. Thesespecifications are required because animals are [a] complex unities ofmatter (body) and form (soul); [b] arise by a complex process ofdevelopment; [c] the end—that for the sake of which thedevelopment occurs— is both causally and definitionally prior tothat process; [d] a distinctive kind of necessity, conditionalnecessity, is operative; and [e] a special method ofmulti-differentiae division is required. Such a discussion is requiredby the fact that although thePosterior Analytics intends itsepistemic standards to be applicable to natural science – as isclear from the many examples drawn from natural science in book II– it provides no details as to how this application is to beaccomplished.

What, then, doesPA I tell us about the proper way toinvestigate animals? Aristotle begins by posing a problem about how toidentify the proper objects of investigation. Should we begin bystudying the features of groups close to the level of perception, suchas human beings, horses, dogs and such, or should we look forattributes that ‘belong in common according to kind, and thenlater study their distinctive attributes’ (639b4–5). Henotes that since there are many attributes that are common to many ofthese more concrete kinds, focusing our study on them will have theresult of our repeating ourselves—much as if, to use an examplefromAPo II discussed in Section 2, we were to remain at thelevel of ‘olive trees lose their leaves’, ‘grapevines lose their leaves’. Among these common attributes,Aristotle distinguishes those that seem not to differ across the kindsthat have them (he cites respiration and death) from those that are‘ distinctive in form ’ such as locomotion. As he puts it:“it is apparent that locomotion is not one in form, becauseflying, swimming, walking, and crawling differ” (639b1–2).Aristotle deals with this question, so reminiscent ofAPo. I4–5, inPA I 4, but only after he has introduced a newway of thinking about differentiae and division appropriate forinvestigating animals. After discussing his recommendations regardingthe use of logical division in biology, we will return to look at hisanswer.

Animals are complex structures organized so as to be able to performan integrated set of functions and activities; yet thePosteriorAnalytics provides one with very little guidance as to how toapply its norms to such things. AgainPA I, and especiallychapters 1 and 5, appears designed to provide that guidance. It seeksto establish [a] the priority of goal-causation to motive-causation,[b] the priority of the study of an animal’s form (which, heargues, should be identified with its soul) to the study of itsmaterial constituents (i.e. its body), and [c] the presence of aspecial kind of necessity operative where goals and form takepriority, namely hypothetical or conditional necessity (cf.PA I 1, 640a10–641a32, 642a1–31).

The argument is complicated in virtue of its manner of presentation.First, it is a narrative in which Aristotle gradually develops his ownviews by exposing the errors of those who investigated nature beforehim; it is structured as presenting an alternative to views expressedby Empedocles and Democritus, and as in the spirit of Socrates(642a24–31). Second, as is so typical of him, what initially mayappear to be three separate narratives turn out to be a single,complex case for emphasizing the study of form, teleologicalexplanation, and conditional necessity when studying living things.Form, in the case of living things, turns out to be the capacity toperform living functions such as nutrition, perception, or locomotion,i.e. soul; and thus the form of a living thing is causally prior tothe matter, because it is the goal for the sake of which the parts ofthe animal—its matter—come to be and exist. This, in turn,provides us with the appropriate way to understand ‘conditionalnecessity’—parts and the processes that produce them donot necessitate the outcome; on the contrary, the outcome necessitatesthat the developmental processes bring about the parts that arenecessary for the organism to live its life, and do so in a temporallyand spatially coordinated manner (cf.GA II 4,740b19–34; II 6, 743a16–36).

Chapters 2 and 3 have a similar narrative structure. Gradually, apositive theory of biological division emerges from the ashes of adetailed critical analysis of those (Plato and certain of hisstudents) who “attempt to grasp the particular by dividing thekind into two differences” (PA I 2, 642b5), a practicehe finds in “the written divisions” (642b11), perhaps areference to divisions we find in some of Plato’s laterdialogues, or perhaps to lost works by other members of Plato’sAcademy. The method he is criticizing combines two basic techniquesthat lead to things being grouped together that are fundamentallydifferent and things being grouped separately that are fundamentallysimilar: dichotomy and division by non-essentials. Dichotomy is themethod of dividing the more general differentia into two exhaustivealternatives, which often entails that one of the alternatives issimply the privation of the other (winged, wingless). Division bynon-essentials involves dividing a prior differentia-class by means ofan unrelated difference. For example, you might first divide animalsinto winged and wingless, and then winged animals into wild andtame.

I mean the sort of thing that results by dividing animals into thewingless and the winged, and winged into tame and wild, or pale anddark. Neither tame nor pale is a difference of winged; rather each isthe origin of another difference, while here it is incidental.(PA I 3, 643b19–22)

To avoid the problems created by this dichotomous and arbitrarymethod, Aristotle recommends a method that divides each widerdifferentia by more and more determinate forms of that differentia(wings into forms of wing, beaks into forms of beak), and does sosimultaneously on as many differentiae as are correlated at a givenlevel of universality.

Rather, one should try to take animals by kinds, following the lead ofthe many in demarcating a bird kind and a fish kind. Each of these hasbeen defined by many differences, not according to dichotomy.(PA I 3, 643b9–12)

Thus, if all birds have beaks, feathers, wings of a sort, are bipedal,etc. , the biologist needs to perform the proper sort of division onall of these in order to grasp the various sub-kinds of bird. Thiswill not, of course, give us demonstrative knowledge; but it will helpus to grasp the co-extensively correlated features, at each level ofspecificity, that are the proper things about which to seekdemonstrative knowledge.

An interesting feature of this extended criticism of dichotomous,arbitrary division and the development of a systematic,multi-differentiae alternative is that it takes for granted the‘naturalness’ of certain kinds that ‘the many’have identified. As he says above, ‘these [birds and fish] havebeen defined by many differences’; earlier he had said that theterms ‘bird’ and ‘fish’ name a‘similarity’, a group of animals that are ‘alike inkind’ that dichotomous division inappropriately tears apart(642b13–19). During the discussion of division there is verylittle clarification of what underlies this notion of similarity orlikeness in kind. However, armed with a method of division suited tothe study of animals, the discussion quickly turns to the question ofwhat it is that makes it appropriate to treat all birds or all fish asa single kind, and to the specification of rules for identifying othersuch kinds. What ‘bird’ and ‘fish’ name are,he claims, kinds with “common natures, and forms not very farapart” (644b2–3). Prior to understanding these kindsthrough a scientific account of this common nature, we can—asthePosterior Analytics argues—grasp these kinds, i.e.grasp that all birdshave a common nature.^[8] We do this by noting that they have many general differences thatvary in measurable ways—by the more and less, as he puts it.

…[these kinds] are correctly defined in this way. For thoseanimals that differ by degree and the more and the less have beenbrought together under one kind, while those that are analogous havebeen kept apart. I mean, for example, that bird differs from bird bythe more or by degree (for one has long feathers, another shortfeathers), while fish differs from bird by analogy (for what isfeather in the one is scale in the other). (PA I 4,644a16–22)

It is with this very topic of different degrees of similarity anddifference of parts that theHistoria Animalium begins,extending this way of characterizing similarity and differenceimmediately to differences in activities, ways of life and traits ofcharacter. (HA I 1, 486a5–487a13) This is, then,clearly a discussion of how one achieves ‘knowledge of thefact’, rather than ‘knowledge of the reasonwhy’.

The closing section ofPA I (treated since the Renaissance asits fifth chapter) is often thought of as having two, essentiallyunrelated parts. And there is some justification for this; if one wereto remove the first half of the chapter, one would be left with anargument the flows quite naturally out of the conclusion of chapter 4.At that point, Aristotle states that once one has made an initialdivision of the attributes that belong to all the animalsperse, the next step is to attempt “to divide theircauses,” after which he applies the analysis of sameness anddifference from the previous discussion of parts to the activitiesperformed by these parts. He then closes the discussion by arguingthat the differences we find in animal parts are to be explained byreference to differences found among their activities. Thus a properdivision of activities is a division of the causes of the parts ofanimals.

Nevertheless, a good case can be made that this ‘chapter’forms a coherent whole, a sort of culmination of the book. It beginswith perhaps the best known passage in Aristotle’s biologicalworks, a stirring and beautifully crafted encomium to the joys ofstudying animals, even the most lowly. An elegant introduction dividesnatural beings into those that are eternal and those that partake ofgeneration and perishing, noting that there are attractions tostudying both: though access to information about the former islimited, he likens it to “…a chance, brief glimpse of theones we love”; on the other hand the latter, perishable things“take the prize in respect of understanding because we know moreof them and know them more fully” and they are “more ofour own nature” (644b23–645a3). He then elaborates on thevalue of the study of the living things around us. It is a passageworth quoting in full.

Since we have completed stating the way things appear to us about thedivine things, it remains to speak about animal nature, omittingnothing in our power, whether of less or greater esteem. For even inthe study of animals disagreeable to perception, the nature thatcrafted them likewise provides extraordinary pleasures to those ableto know their causes and who are by nature philosophers. Surely itwould be unreasonable, even absurd, for us to enjoy studyinglikenesses of animals—on the ground that we are at the same timestudying the art, such as painting and sculpture, that madethem—while not prizing even more the study of things constitutedby nature, at least when we can behold their causes.

For this reason we should not be childishly disgusted at theexamination of the less valuable animals. For in all natural thingsthere is something marvelous. Even as Heraclitus is said to havespoken to those strangers who wished to meet him but stopped as theywere approaching when they saw him warming himself at theoven—he bade them to enter without fear, ‘For there aregods here too’—so too one should approach research abouteach of the animals without disgust, since in every one there issomething natural and good. For what is not haphazard but rather forthe sake of something is in fact present most of all in the works ofnature; the end for the sake of which takes the place of the good. Ifsomeone considered the study of the other animals to lack value, heought to think the same thing about himself as well; for it isimpossible to look at that from which mankind has beenconstituted—blood, flesh, bones, blood vessels, and other suchparts—without considerable disgust. Just as one who discussesthe parts or equipment of anything should not be thought of as doingso in order to draw attention to the matter, nor for the sake of thematter, but rather in order to draw attention to the overall shape(e.g. to a house rather than bricks, mortar, and timbers); likewiseone should consider the discussion of nature to be referring to thecomposite and the overall substantial being rather than to thosethings which do not exist when separated from their substantial being.(PA I 5, 645a4–36)

Readers, often carried away by the rhetoric of this passage, mightfail to notice that there is a compelling argument here, with two keyconclusions. The first is that, while studying the Sun, Moon, startsand planets may be a noble pursuit, if scientific understanding isyour goal, you are much more likely to achieve it in the study ofanimals and plants: “…anyone wishing to laborsufficiently can grasp many things about each kind…we know moreof them and we know them more fully…they are nearer to us andmore of our own nature…” (excerpted from644b29–645a3). The second is that if one has the properphilosophical focus, then one realizes that the somewhat unpleasanttask of dissecting blood vessels and the like, is a means tounderstandingthat for the sake of which andsoul,those objects of inquiry argued to be primary in chapter 1. For thelesson of chapter 1 is that understanding living matter is achievedprimarily by means of an understanding of the functional goals servedby an animal’s parts, discovering what each of its parts is for,what it contributes to the life of the animal. This is thephilosophical way to investigate animals, and by doing so you learnthe value of an animal’s parts and activities to its life.

The remainder of the chapter, therefore, recommends approaching theactivities associated with animals and their parts in amanner exactly analogous to the approach to the study of partsrecommended in chapter 4 (645b1–14); and it concludes with aschematic discussion of the variety of teleological relationships thatholdamong parts,between parts and theiractivities, andamong activities. Aristotle encourages us toconceive of these relationships in a yet moreunified way, asa single complex relationship between a single complex activity(living, I suppose) and a single complex instrument, theanimal’s body. (645b15–36)

In the first book ofOn the Parts of Animals, then, we have asystematic philosophy of biology, which in many respects seems toprovide what is missing in theAnalytics regarding theapplication of its program to the study of living nature. But doesAristotle’s biological practice carry through on this program?It is worthwhile keeping that question in mind as we survey thosebooks that report the results of Aristotle’s animal studies. Tothose books we now turn.

5. Aristotle’s Biological Practice

5.1 TheHistory of Animals as a Report of the Results of aHoti-Investigation

As we saw earlier, Aristotle introduces his systematic study of thedifferences and attributes of animals as ahoti-investigation, a factual investigation preliminary tothe search for causal demonstrations. By studying it, then, we oughtto be able to develop a rich picture of what this theoreticallymotivated, preliminary stage of investigation aims to achieve, andperhaps a glimpse of what such an investigation entails.

As many studies, following up on the pioneering work of David Balme(1961, 1987b) have now established, theHistory of Animals(HA) is a work that from first to last displays and buildsupon multi-differentiae division of animal differences (see Gotthelf1988, 1997b; Lennox 2001b, chs. 1, 2; Pellegrin 1986). It is organizedas a study of four kinds of animal differences first mentioned inHA’s first chapter as the principal objects of study(at 486b22–487a14)—differences in parts (the topic ofBooks I–IV), in modes of activity and ways of life (thoserelated to generation in Books V–VI—and human generation inIX—others in Book VII) and in characters (Book VIII). These in turnare sub-divided; for example, discussion of thenon-uniformparts (organs, as we say) of animals with blood (I 7–III 1) isfollowed by that of theiruniform parts (tissues, III2–22). A discussion of the parts of animals without blood thenconcludes the discussion of differences in parts (IV 1–8). BookIV concludes with a discussion of differences in sensory faculties,voice, and differences related to sex.^[9]

It is only once Aristotle begins to distinguishdifferencesamong, say, uniform parts that various groupings of animals play animportant role in organizing the discussion. And in so far as thereare relatively stable general groupings of animals, these areidentified by noting their possession of stable correlations amongdifferentiae—for example, there are a large number of differentanimals all of which have wings, feathers, beaks, and two fleshlesslegs, and this group of animals has been given the designation ‘bird’.^[10] In other cases, such groups have not been generally recognized, andAristotle simply refers to them by means of some of their mostimportant correlated differences—the four-legged andlive-bearing animals, for example, corresponding to our land mammals(with one important exception).

What is clear from the practice of theHistory of Animals isboth the value of division and its limitations. Division by itselfdoes not provide you with theaxes of division; rather theyare presupposed. Division does not give you animal kinds; as we saw inthe previous section, one needs to turn toPA I 4 andHA I 6 for Aristotle’s thoughts on how those kinds areestablished. Something besides division is needed in order for aresearcher to recognizetheoreticallysignificantkinds, such as cephalopods or cetaceans. Why group animals togetherbased on their possession of four legs and the ability to give birthto living offspring (rather than eggs)? Certainly each of these traitsis the product of a division, one of modes of locomotion and one ofmodes of reproduction. But those divisions do not tell you thatanimals with four legs that bear living young constitute ascientifically significant group.

A second limitation of division is its indifference to the distinctionbetween causally fundamental characteristics and proper attributes, touse the language of theAnalytics. Yet, being able todistinguish these is absolutely fundamental to Aristotelian science. Acareful comparative study of theHistory of Animals, on theone hand, and works such asOn the Parts orOn theGeneration of Animals, on the other, provides insight into howAristotle understands and deploys this distinction in his actualscientific practice. And as we have seen above, Aristotle drawsexplicit attention to its importance for his biological investigationsin a number of key texts within those investigations themselves. Tostudy in detail the interplay between definition, causal demonstrationand division in the biology is to see Aristotle working through justthose problems which form the central question ofPosteriorAnalytics II—how precisely are definition, causaldemonstration and division related to one another in the quest for,and achievement of, scientific understanding?

It is impossible to present even a hint of the richness of theempirical content of theHistoria Animalium here. Beforegoing on to a discussion of the works that report the results ofAristotle’s causal investigations of animal parts and animalgeneration, however, two examples of reports fromHA areprovided for comparison with corresponding discussions inPAandGA. The first example discusses the organs of respirationin blooded animals; these are the firstinternal organsdiscussed after Aristotle has concluded his review of theirexternal parts. Here is how he introduces thatdiscussion.

So, then, the number and character of the external parts of theblooded animals and how they differ from one another has been stated.We must now discuss how the internal parts are situated, first in theblooded animals.

As many as (hosa) are four legged and live-bearing all(panta) have an esophagus and windpipe, arranged just as inhuman beings; it is also arranged similarly in as many of the fourlegged animals as lay eggs, and in the birds; but they differ in theforms (tois eidesi) of these parts. Generally, all and only(panta hosa) those receiving air by inhaling and exhaling inevery case (panta) have a lung, windpipe and esophagus; andtheposition of the esophagus and windpipe is alike in all,but the organs are not, while the lung is neither alike in all nor isit positioned in a like manner. And again as many as (hosa)have blood all (panta) have a heart… . But not all[blooded animals] have a lung, for instance fish do not, nor any otheranimal there might be that has gills. (505b23–506a12,excerpts)

There are a number of features in this passage that are commonthroughout theHistoria Animalium and provide insight intoits methods and aims. First is the syntactically redundant linguisticpatternhosa…panta (“as many as...all”),variants of which are common in this treatise. Aristotle appears touse the sentence form “As many as are X, all have Y” for aquite specific reason. It is notjust to note a universalcorrelation; it is to do so while leaving the extension of thecorrelation open—a brilliant methodological innovation. Newanimals with the correlation can be discovered, but the generalizationwill not change, since it is about the universal correlation amongdifferentiae—in this case internal organs—not about thekinds that exemplify it. It appears that when Aristotle intensifiesthe expression by writingpanta hosa, as he does once here,he means to signal aconvertible universal, an‘entailment’ as we would say. Aristotle first lists anumber of distinct groups, all the members of which have the threeorgans being discussed, windpipe, lung and esophagus. Then, using theterm ‘generally’ to signal what he is about to do, heidentifies a differentia that all these groups have in common, andwhich iscoextensive with these three organs—inhalingand exhaling air. The inductive pattern has the following form:

‘As many as areP all haveY; As many as areQ all haveY… .

Generally, all and only those that areX (a feature common toP,Q…) haveY’.

By going on to note that as many as have blood have a heart, heimplicitly is warning the reader about a potential false inference onemight draw from the examples so far: that all blooded animals have alung. He mentions fish as an example of blooded animals without alung, but immediately identifies therelevant differentia:‘those blooded animalsthat have gills do not havethese organs [the lung and its associated parts]’. He is carefulnot to restrict the universal to a kind—the relevant correlationis withgills, in whichever animals they might be found.

While the inductive strategy of this work, directing us to high-level,convertible universals is, I hope, now clear, it is also important tonote what isabsent from this passage. Aristotle rarely inthis work claims any of these correlations isnecessary, orthat others areimpossible. He does not distinguish featuresthat are part of theessence of a kind from others that aremere attributes; and he typically avoids any hint ofcausalexplanation. All of this is to be expected, given themethodological guidelines forhistoria that we discussedearlier—historia is preliminary to causal investigationand prepares us for it. In the passage we are currently considering,for example, it is striking that he notes the convertible correlationbetween lung, windpipe and esophagus, on the one hand, and inhalingand exhaling of air, on the other, but doesnot claim thattwo of the organs are present for the sake of breathing. (In fact, theword for ‘breathing’ is never used!) Though he uses theterm ‘nature’ regularly inHA, he doesnot, as he does so often in his causal investigations, claimthat nature does nothing in vain, or that it always does what is bestfor each organism. Nor does he talk about the parts of an animal asits material nature, nor about its living capacities as aspects of itsformal nature. Indeed there is virtually no mention of the matter-formdistinction inHA. It is only when we turn to the variousbiological treatises devoted to causal investigation that thislanguage associated with the search for definitions and demonstrationscomes to the fore.

The aim of this brief analysis of one small passage is to convey ataste of the methodological depth and complexity of this greatscientific treatise, so often misunderstood as a poorly organizedcompendium of nature lore. I’ll conclude this section with onemore example, from the books dealing with generation, so that we maycompare it with a corresponding discussion inDeGeneratione Animalium.

HA V–VI discuss all aspects of animal generation, moving fromconsideration of differences in modes and timing of copulation andreproduction to the actualprocess of generation (or‘development’, as we more often say). As in his discussionof parts, he moves through the various blooded kinds and thendiscusses generation in bloodless kinds and from identifying theuniversals common to all members of a group to identifying thepeculiarities of more specific kinds. AtHA VI 3, havingpreviously described the common and peculiar characteristics ofcopulation in birds, he turns to recording his observations of thedevelopment of the chick at the critical fourth day after the egg hasbeen laid.

Generation from the egg occurs in an identical manner in all birds,though the time taken to termination varies, as we have said. In thecase of the hen, the first signs of the embryo are seen after threedays and nights; in larger birds it takes more time, in smaller birdsless. During this time the yolk travels upwards to the point of theegg—that is where the starting point of the egg is and where itopens up, and the heart is no bigger than just a small blood-spot inthe white. This spot beats and moves as though it were alive; and fromit, as it grows, two vein-like vessels with blood in them lead on atwisted course to each of the two surrounding membranes. A membranewith bloody fibers already surrounds the white of the egg, at thistime coming from the vessel-like channels. A bit later the body canalso be distinguished, at first very small and pale. The head isapparent, and its eyes, very swollen; and this continues for a longtime, for it is later that they contract and become smaller.(561a4–21)

He begins with a wide generalization about all birds, followed by a‘more and less’ correlation between thesize ofthe bird and therate of development. This device allowsAristotle to use the careful description of the chick egg opened onday four as a universal description of development; the reader islicensed to infer that the same stage of development will occur in allbirds, but may occur either earlier or later, depending on whetherthey are larger or smaller than the domestic chicken.Aristotle’s description of this classic experiment led to itsbeing repeated many times in the Renaissance.^[11] Anyone who has seen modern films of the chick at this stage ofdifferentiation can appreciate the accuracy of Aristotle’sdescription, especially when one takes into account the size of thechick embryo at this stage of growth.

5.2 From Inquiry to Understanding; fromhoti todioti.

For Aristotle, ‘historia’, the scientificorganization of information about animals—serves the goal ofcausal explanation; and, as I discussed in section 4., explanation byreference to goals and functions is the primary form of causalexplanation in biology.

On the Parts of Animals II–IV presents Aristotle’sattempt to provide causal explanations for the sort of information onefinds organized inHA I–IV, information about the uniform andnon-uniform parts of animals. (PA I, it will be recalled, isa discussion of the norms that are needed to guide the scientificinvestigation of animals; see section 4, above.) Here, I will benarrowly focused on just a couple of passages inPA II–IV,but will begin with a very brief sketch of its overall structure. Itbegins (PA II 1–2) with a careful and complexdiscussion of the causal relationships between uniform and non-uniformparts (roughly, this distinction corresponds to our distinctionbetween bodily fluids and tissues and organs), stressing theteleological priority of the whole organism to the parts, and amongparts the priority of the non-uniform to the uniform.PA II3–10 then discusses the uniform parts, beginning with that outof which all the others are nourished, blood, and ending with flesh,bone, and analogous materials (nail, horn, hoof). From II 10 to III 3,Aristotle discusses the external parts of blooded animals associatedwith the head such as eyes, ears, nose and mouth. But when he gets tothe neck, he turns to the internal parts, and from III 3 to IV 4 hediscusses the ‘innards’ of the blooded animals, parts suchas heart, lung, liver, kidneys, and so on. From IV 5 to 9 he discussesthe parts, both internal and external, of the ‘bloodless’animals, i.e. the crustaceans, testaceous mollusks, cephalopods andinsects. Finally, at IV 10, he returns to the external partsassociated with the torso and limbs of the live bearing and egg layingquadrupeds (10–11), birds (12), and fish (13); and ends bydiscussing a number of animals that ‘dualize’ betweenbeing land-dwellers and water dwellers or flyers.

In order to compare the methods of this treatise with the discussionof the parts inHA, it will be useful to look briefly atPA III 3, a discussion of the lung, windpipe and esophagus,the part discussed in the passage from HA II quoted in section 5.1,above.

Not all animals have a neck, but only those with the partsfor thesake of which the neck isnaturally present—theseare the windpipe and the part known as the esophagus. Now the larynxis presentby nature for the sake of breathing; for it isthrough this part that animals draw in and expel air when they inhaleand exhale.This is why those without a lung have no neck,e.g. the kind consisting of the fish. The esophagus is the partthrough which nourishment proceeds to the gut; so that animals withoutnecks manifestly do not have an esophagus. Butit is notnecessary to have the esophagusfor the sake ofnutrition; for it concocts nothing. And further, it ispossible for the gut to be placed right next to the positionof the mouth, while for the lung this isimpossible. Forthereneeds first to be something common like a conduit,which then divides in two and through which the air is separated intopassages—in this way the lungmay best accomplishinhalation and exhalation.

So, then, the organ connected with breathingfrom necessityhas length; therefore it isnecessary for there to be anesophagus between the mouth and the stomach. The esophagus is fleshy,with a sinuous elasticity—sinuousso that itmay dilate when food is ingested, yetfleshyso thatit is soft and yielding and is not damaged when it is scraped by thefood going down. (664a14–34)

I have highlighted the language ofnature, necessity, possibility(and impossibility), and being for the sake of in this passage inorder to highlight the contrast with the discussion of the sameorganic correlations in the correspondingHA passage. Herethe goal isexplanation—parts are present and have thecharacter they do primarily due to the conditional necessity imposedby the organism’s functional requirements. One sees here theAristotle that so impressed the great French naturalist GeorgesCuvier: Aristotle is not only systematically discussing the adaptivefunctions of each of these organs; he is also displaying the complexway in which the internal parts of animals constitute an organicsystem.

The lack of names for animal kinds is also noteworthy; as in thecorresponding passage fromHA II, fish are mentioned once asan instance of blooded animals that lack the organs in question; butthe stress throughout is on this particular system of organs inwhichever blooded animals have them. Aristotle’s goal is toexplain why it is that certain animals have these organs, and why itis that,if they have one of these organs, theymusthave the others. Some, but not all, of the explanations specify thefunction for the sake of which the parts are present; and even thematerial nature of the tissues, whether fleshy or sinuous, may beexplained in functional terms. This discussion also displays ahierarchy of teleological connections of the sort describedat the close ofPA I 5, 645b28–33—one activity ispresent for the sake of another more basic one; a part that performs asubordinate activity is present for the sake of a part that performs amore important activity. Inhaling and exhaling are for the sake ofrespiration (which is for the sake of cooling the blood); a windpipeis present for the sake of transporting air to and from the lung; aneck is present to protect the windpipe.

For reasons that will become clear, the relationship between the booksof theHistoria Animalium dealing with generation andOnthe Generation of Animals (GA) is somewhat more complex.GA has a reasonably clear organization of its own; but itscentral (though notonly) project of explaining the causalroles of the male and female in sexual generation and the causality ofembryological development raises a host of topics and problems wellbeyond the scope ofHA. But a study of how the two works arerelated is nonetheless illuminating. This discussion ofAristotle’s biological practice will thus close by consideringthe causal explanation of embryological development and in particularthe explanation for the early appearance of the heart, with a finallook at the application of this explanation to the case of embryonicbirds.

As I noted earlier, taken on its own terms,GA has areasonably clear structure. Here again, as with PA II–IV, I will beginwith a brief sketch of its overall structure, before focusing narrowlyon its method as applied to one problem. It begins (715a1–18) bynoting that it will explain two sets of facts left unexplained inPA: the differences among the parts related to generation;and thegeneration of the parts generally. Though heacknowledges that some animals do not have males and females, hetreats sexual generation as his central topic. Initially he provides atheoretically ‘neutral’ account of the distinction: themale is what generates in another, the female what generates in itself(716a14–15). It is not until late in book I that he begins todevelop his own detailed theory of their distinctive contributions togeneration.

The first 13 chapters characterize the reproductive organs in themales and females of blooded animals, while 14–16 do the samefor the bloodless animals that have males and females. Beginning inchapter 17, the discussion turns to the relevantuniformparts related to generation,sperma (roughly‘seed’) and milk, but the discussion of milk is postponeduntil book IV. This immediately raises the contentious issue ofwhetherboth male and female contributesperma, andif both, then what the nature of their respective contributions is.This is a large part of the discussion from I 17–II 5, one of the mostdifficult stretches of text in the Aristotelian corpus, and the one onwhich our attention will be focused. But to continue our overview: theremainder of book II (from chapter 5 on) discusses the causes of theembryological development of live-bearing animals, while theegg-laying animals are the primary focus in book III, which closeswith a discussion of animals that arenot sexually generated,including those that arise ‘spontaneously.’GA IVturns to the development of inherited differences within kinds,beginning with the most important intra-specific difference for histheory of generation, the difference between male and female. Fromthere it moves on to family resemblance, differences in the number ofoffspring produced and to the causes of deformities.GA Vaims to explain ‘more and less’ variations within kindsthat appear late in development and that may be fully accounted for byidentifying material level causal interactions—differenceswithin a kind in the color, texture or density of a part, forexample.

The remainder of this discussion will focus on the general causaltheory of animal generation developed in the first half ofGA II.^[12] In the closing chapters of book I, Aristotle argues that both themale and female contributions are formed from a ‘usefulresidue’ of blood by a concocting process, the male’sbeing more fully concocted than the female’s. From this point onthe male’s contribution is typically termedgonê(semen), and the female’skatamenia (menses). Aristotleis not entirely consistent, however: occasionally he uses the generictermsperma for the male contribution and explicitlycontrasts it withkatamenia (727a27–30); while at othertimes he refers tokatamenia as a sort ofsperma(728a26–29).

The two contributions are variously described. The male contributes asource of movement ordunamis (‘power’ or‘potential’), which, as the argument unfolds, turns out tobe a special sort of capacity to heat present in the semen’spneuma or air, which is part of its nature. (This gets fullyworked out inGA II 2–3) The semen itself is mere avehicle for delivering this heating capacity; the male makes nomaterial contribution to the offspring. The female contributes whatmight be called ‘prepared matter’; all it needs is thepresence within it of the heating capacity from the male and it beginsa more or less lengthy and complicated developmental process, whichAristotle analogizes to a sort of automaton performing a complex setof coordinated movements once it is set in motion.

He relies at several points in the argument on an analogy with crafts,such as house building:

In animals that emit semen the nature in the male uses the semen as aninstrument possessing active movement, just as the tools are moved inthings that come to be by craft; for the movement of the craft issomehow in these tools. (730b20–23)

This obscure analogy gradually gets unpacked in the first fourchapters ofGA II. The general principle common to art andnature is this:

As many things as come to be by nature or by art come to be by meansof a being in actuality from that which is potentially such as thatbeing. (734b22–23)

It is the prepared portion of the female’skatameniathat is potentially such as the contributor of semen is actually. Andthe semen conveys to it a movement or power, such that “when themovement ceases each of the parts comes to be and is ensouled(734b24–25).” That is, in embryological development, eachpart emerges within a system of parts that is organized to providenutrition for its growth, and that is guided by a complex‘program’ for its development. Notice that as each partcomes to be it already has the functional capacity associated withit—it comes to beand is ensouled.

As for hardness, softness, toughness and fragility and all the othersuch affections present in these ensouled parts, these affectionsmight be produced by heat and cold, but not the defining character(logos) in virtue of which the one part is flesh and theother bone; that is the result of the movement derived from thegenerator, being in actuality what that out of which it comes to be ispotentially, just as in things that come to be by craftsmanship.(734b31–35)

This passage comes immediately after Aristotle has stressed tworelated points: that the uniform parts and the instrumental partsarise simultaneously; and that even flesh and bone have a function toperform. These points are tightly connected. The defining features oftissues are not merely their affective qualities such as being hard orsoft, but their biological functions as well; and their biologicalfunctions are intimately connected to their roles inconstituting—and being able to play functional rolesin—instrumental parts; many, if not all, of a part’saffective qualities are a consequence of its biological role.

In the process of making this argument, Aristotle also stresses acrucial and problematicdis-analogy: Natural things, oncetheir generation begins, ‘grow by means of themselves’(735a13–14). This is the most fundamental difference between artand nature for Aristotle; a nature is a source of change within thething itself (Physics II. 1). Natural development, then,though initiated by the warmth contributed by the male parent,continues by means of a source of change within the developing embryo.The carpenter may not mix any of his own material in his buildings;but he must be continuously, physically involved in the movements thatcreate those buildings. Not so with the male parent in naturalgeneration. So how does a complex process that has its origins in anexternal generator become a natural process of development?

For Aristotle, the heart (or its analogue in bloodless animals) iscrucial. It is the first part created by the heat derived from thesemen of the male parent, and henceforth it is the primary internalsource of that heat and thus of further development (735a16–26).The following explanation begins to bring us into contact with ourpassage on generation from theHistory of Animals.

…in the embryo (kuema), while in a way all the partsare present potentially, the source [of development] is most along thepath to actuality. This is why the heart is first to be differentiatedin actuality. And this is not only clear to perception (as ithappens), but is also clear to reason. When the developing thing isdistinct from both the male and female contributions, it must manageitself, as when a son sets up a home away from his father. So inanimals there must be a source of generation from which the laterorganizing of the body comes about. … Wherefore the heartappears differentiated first in all blooded animals; for it is thesource of both the uniform and the non-uniform parts. … And theprepared blood or its analogue is nutrient for the animal, and theblood vessels are its repository; for this reason the heart is theirsource. This is clear from a study of ‘the histories’ and‘the dissections’. (740a2–23, excerpted; compare735a12–26, 738b17–18 740a27–36, 742b34–743a1,743b26)

Having developed this general explanation during his discussion of hiscentral case, viviparous development, inGA II, Aristotlemoves on to egg-laying animals in book III.GA III 1 carriesover to them whatever is common to the two cases, with discussion ofthe development of birds in their eggs beginning inGA III 2.A recurring aspect of his argument, here as inPA, is torefer us for descriptive details to thehistories (presumablythe basis of ourHA) and to a collection of representationsof dissections (tragically not preserved, but cited repeatedly inAristotle’s biological writings and in ancient catalogues of hiswritings).

The most general differences among egg-layers relate to the‘completeness’ of the egg when laid. Because birds layeggs that become hard as soon as they are exposed to the air(752a30–b2), they are taken to be better prepared when laid than theeggs of other egg-laying animals. Ignoring much interesting andimportant detail, we will take up the discussion of development withinthe eggs of birds as they incubate. Aristotle distinguishes the‘white’ and the ‘yolk’, not descriptively ashe did inHA, but functionally (752b18–28).

…it is the white out of which the animal is constituted, whilethe yolk becomes nutrient, and growth for the constitution of theparts is from it. This is also why the yolk and the white, havingdistinct natures, have been kept distinct by membranes. For precisedetails concerning how these parts are situated in relation to eachother in virtue of the sources of generation and the constitution ofanimals, as well as the membranes and umbilical cords, one shouldstudy what has been outlined in the histories. The following appearsto be sufficient for the present investigation: the heart is the firstthing constituted; after this the great blood vessel is marked off,and two umbilical cords extend from this blood vessel, one to themembrane around the yolk, the other to the membrane surrounding theanimal itself. This latter is thus next to the membrane of the shell.(753b11–23)

In this case (though not always) one does get far more detail inHA. These references to histories and dissections can bemisleading unless one takes into account the differences in the aims,and thus in the organization, of these treatises. In this case, forexample, nothing is said inGA about the heart ‘beatingand moving as though it were alive’. As we saw, however,GA II stresses that in the development of live-bearinganimals, the heart is first to be formed, is ensouled from the start,and is the source of development for all the other parts—a muchmore ‘theory-laden’ characterization that stresses theheart’s causal role in development. And because of theorganizational structure ofGA, much of what is said in hisdiscussion of the live-bearing animals (those that are ‘morecomplete’ when they are born) is assumed to apply to animalsthat lay eggs (that are ‘less complete’ when born).

Recall the stunningly accurate discussion of the head and eyes of thefour day old chick embryo inHA (in section 5.1, above). Thisis not discussed inGA III 2; however inGA II 6, ina long discussion of early organ formation inlive-bearinganimals, Aristotle has a good deal to say on the subject:

What happens concerning the eyes of animals presents a problem. Forfrom the beginning, whether in land animals, swimmers or flyers, theyappear very large and yet they are among the last of the parts to becompleted and in the mean time contract in size.This isbecause the sense organs of the eyes are, as with the other senseorgans, on channels; but while those for touch and taste are simplybodily, or some part of the body of animals, and those for smell andhearing are channels connected to the air outside and are full ofconnate pneuma…the eyes alone have a proper sensory body.(743b33–744a6)

The full explanation goes on much longer, but we need not follow itout for the purposes of making two important points about therelationship ofGA toHA. The first is that theorganization ofGA dictates that for the explanation of factsof wide generality such as this one, we must look in bookII—notice that he claims that this explanation for the largesize of eyes early in development and for their subsequent contractionapplies to all land, air and water animals. The second point to bestressed is the relentlessly causal/explanatory focus of theGA discussion, a feature (properly) completely absent in thecorresponding discussions inHA. As impressive as thedescriptive accuracy of the embryological passage cited earlier fromHA is, we again need to remember what isabsent fromthat discussion. For the equally impressive embryologicaltheory, the reader of Aristotle’s biology must turn totheGeneration of Animals.

6. A Concluding Puzzle

This entry on Aristotle’s biology and its philosophy closes witha puzzle about the organization of his biological works when comparedwith the remainder of the Aristotelian corpus. I began by noting thatit is a fundamental aspect of Aristotle’s theory of science thatinvestigation proceeds from a stage where one establishes theexistence of the things being studied and the facts about them to astage where the focus is on causal explanations by reference to thenatures and essences of those things. It seems clear that thebiological works honor this distinction, and do so self-consciously.Yet Aristotle never suggests, in thePosterior Analytics oranywhere else, that these stages should be represented bydistincttreatises devoted to the same subject. Indeed, in no other domaindoes Aristotle do this: whether we look to meteorology, cosmology,psychology, ethics, drama or rhetoric, we find single treatisespresenting both the facts and their explanation. Nor can this puzzlebe easily dismissed as an artifact of later editing—as I havepointed out a number of times, these treatises have a most interestingand consistent pattern of cross-referencing. The treatises that reportthe results of causal investigations regularly refer toHA(and the dissections) for more detail regarding the facts beingexplained; theHA, in contrast,never refers to thecausal treatises. Moreover, the striking avoidance in theHistoriaAnimalium ofall of the concepts associated withdefinition and explanation cannot reasonably be laid at the feet ofsome imagined later editor. We are left, then, to ponder what it wasabout the investigation of animals that led Aristotle to take amethodological distinction regarding stages of investigationand reify it in methodologically distinct treatises devoted to thesedifferent stages.

Bibliography

Selected Texts, Translations, Commentaries

• Balme, D. M., 1991, Aristotle.History of Animals, BooksVII–X, Cambridge, MA: Harvard University Press.
• –––, 1992,Aristotle. De Partibus AnimaliumI and De Generatione Animalium I (with passages from II. 1–3)With a Report on Recent Work and an Additional Bibliography by A.Gotthelf, Oxford: Oxford University Press.
• –––, 2002,Aristotle: Historia Animalium,Volume I, Books I–X Text (prepared for publication by A.Gotthelf), Cambridge: Cambridge University Press.
• Carbone, A., 2002,Aristotele: Le Parti degli Animali,Milano: Biblioteca Universale Rizzoli.
• Drossaart Lulofs, H. J., 1965,Aristotelis De GenerationeAnimalium, Oxford: Oxford University Press.
• Düring, I., 1943/1980 repr.,Aristotle’s DePartibus Animalium: Critical and Literary Commentaries, NewYork: Garland Publishing.
• Epstein, K., 2019,Aristoteles: Historia Animalium Buch VIIIund IX, Berlin: De Gruyter.
• Kullmann, W., 2007,Aristoteles: Über die Teile derLebewesen, Berlin: Akademie Verlag.
• Lanza, D., Vegetti, M., 1971,Aristotele, OpereBiologiche, Torino: UTET.
• Le Blond, J. M., 1945,Aristote, philosophe de la vie: Lelivre premier du traité sur les Parties des Animaux.Paris: Aubier.
• Lennox, J. G., 2001a,Aristotle: On the Parts of Animals,Oxford: Oxford University Press.
• Louis, P., 1956,Les parties des animaux, Paris:Budé.
• –––, 1961,De la générationdes animaux, Paris: Budé.
• Ogle, W., 1882/1987,Aristotle on the Parts of Animals.New York: Garland.
• Peck. A. L., 1961,Aristotle: Parts of Animals(introduction, text, translation), Loeb Classical Library. Cambridge,MA: Harvard University Press.
• –––, 1963,Aristotle: Generation ofAnimals (introduction, text, translation), Loeb ClassicalLibrary. Cambridge, MA: Harvard University Press.
• –––, 1965,Aristotle: Historia Animalium,Books I–III (introduction, text, translation), Loeb ClassicalLibrary, Cambridge, MA: Harvard University Press.
• –––, 1970,Aristotle: Historia Animalium,Books IV–VI (introduction, text, translation), Loeb ClassicalLibrary, Cambridge, MA: Harvard University Press.
• Pellegrin, P., 2011,Aristote: Les Parties des Animaux,Paris: GF Flammarion.
• –––, 2017,Aristote: Histoire desAnimaux, Paris: GF Flammarion.
• Primavesi, O. and K. Corcilius eds., 2018,Aristoteles De motuanimalium: Über die Bewegung der Lebenwesen (Greek Text andGerman Translation), Hamburg: Felix Meiner Verlag.
• Rapp, C. and O. Primavesi eds., 2020,Aristotle’s DeMotu Animalium (Symposium Aristotelicum, with Greek Text andEnglish Translation), Oxford: Oxford University Press.
• Ross, W. D., 1949,Aristotle’s Prior and PosteriorAnalytics: A Revised Text with Introduction and Commentary,Oxford: The Clarendon Press.
• Schneiders, S., 2019,Aristoteles: Historia Animalium BuchVIII und IX, Berlin: De Gruyter.
• Whitteridge, G., 1981,William Harvey: Disputations touchingThe Generation of Animals, Oxford: Blackwell ScientificPublications.

Secondary Sources on Aristotle’s Biology

• Anagnostopoulos, G. (ed.), 2009,A Companion toAristotle, Malden, MA: Wiley-Blackwell.
• Balme, D. M., 1961, “Aristotle’s Use of Differentiaein Zoology,” in S. Mansion (ed.),Aristote e lesproblèmes de méthode, Louvain: PublicationsUniversitaires de Louvain, pp. 195–212.
• –––, 1987a, “The Place of Biology inAristotle’s Philosophy,” in Gotthelf & Lennox 1987,pp. 9–20.
• –––, 1987b, “Aristotle’s Use ofDivision and Differentiae,” in Gotthelf & Lennox 1987, pp.69–89.
• –––, 1987c, “Aristotle’s biology wasnot essentialist,” in Gotthelf & Lennox 1987, pp.291–312.
• –––, 1990, “Matter in definition: a replyto G. E. R. Lloyd,” in Devereux & Pellegrin 1990, pp.49–54.
• Bartos, H. and C. G. King (eds.), 2020,Heat, Pneuma, and Soulin Ancient Philosophy and Science, Cambridge: CambridgeUniversity Press.
• Bolton, R., 1987, “Definition and Scientific Method inAristotle’sPosterior Analytics andGeneration ofAnimals,” in Gotthelf & Lennox 1987, pp.120–66.
• –––, 2010, “Biology and metaphysics inAristotle”, in Lennox and Bolton, pp. 30–55.
• Bowen, A. (ed.), 1991,Science and Philosophy in ClassicalGreece, New York: Garland Press.
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• –––, 1990, “Meaning, natural kinds andnatural history,” in Devereux & Pellegrin 1990, pp.145–67.
• –––, 2000,Aristotle on Meaning andEssence, Oxford: Oxford University Press.
• ––– (ed.), 2010,Definition in GreekPhilosophy, Oxford: Oxford University Press.
• –––, 2012, “Teleological Causation,”in Shields 2012, pp. 226–266.
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• –––, 1997, “The Priority of Final Causesover Efficient Causes in Aristotle’sParts ofAnimals,” in Kullmann und Föllinger 1997, pp.127–144.
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• ––– (ed.), 2021,The Cambridge Companion toAristotle’s Biology, Cambridge: Cambridge UniversityPress.
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• Devereux, D. & Pellegrin, P. (eds.), 1990,Biologie,Logique et Métaphysique chez Aristote, Paris:Éditions du CNRS.
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• Föllinger. S. (ed.), 2010,Was ist ‘Leben’?Aristoteles’ Anschauungen zur Entstehung und Funktionsweise vonLeben, Stuttgart: Franz Steiner Verlag.
• –––, 2010, “Das Problem des Leben inAristoteles’ Embryologie,” in Föllinger 2010, pp.225–236.
• Fortenbaugh, W. W., & Sharples, R. W. (eds.), 1988,Theophrastean Studies, New Brunswick: Rutgers UniversityPress.
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• –––, 2018, “Two Ways of Being for anEnd”,Phronesis, 63: 64–86.
• Gill, M. L., 1989, “Aristotle on Matters of Life andDeath,”Proceedings of the Boston Area Colloquium in AncientPhilosophy, 4: 187–205.
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• Gotthelf, A. (ed.), 1985a,Aristotle on Nature and LivingThings: philosophical and historical studies presented to David M.Balme on his seventieth birthday, Pittsburgh: Mathesis.
• –––, 1985b, “Notes towards a study ofsubstance and essence in Aristotle’sParts of AnimalsII–IV,” in Gotthelf 1985a, pp. 27–54.
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• –––, 2012,Teleology, First Principles, andScientific Method in Aristotle’s Biology, Oxford: OxfordUniversity Press.
• Gotthelf, A. & Lennox, J. G. (eds.), 1987,PhilosophicalIssues in Aristotle’s Biology, Cambridge: CambridgeUniversity Press.
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• Henry, D., 2003, “Themistius and Spontaneous Generation inAristotle’sMetaphysics,”Oxford Studies inAncient Philosophy, 24: 183–208.
• –––, 2006a, “UnderstandingAristotle’s Reproductive Hylomorphism,”Apeiron,39: 269–300.
• –––, 2006b, “Aristotle on the Mechanismsof Inheritance,”Journal of the History of Biology, 39:425–455.
• –––, 2008, “Organismal Natures,”Apeiron: A Journal for Ancient philosophy and science, 41:47–74.
• –––, 2011, “Aristotle’s PluralisticRealism,”The Monist, 94(2): 198–222.
• –––, 2013,“Optimality and Teleology inAristotle’s Natural Science,”Oxford Studies inAncient Philosophy, XLV (Winter): 225–263.
• –––, 2019,Aristotle on Matter, Form, andMoving Causes: The Hylomorphic Theory of Substantial Generation,Cambridge: Cambridge University Press.
• –––, 2021, “Essence and Definition inAristotle’sParts of Animals,”BritishJournal for the History of Philosophy, first online 02 Mar 2021doi:10.1080/09608788.2021.1881442
• Johnson, M., 2005,Aristotle on Teleology, Oxford: OxfordUniversity Press.
• Keil, G. and N. Kreft (eds.), 2019,Aristotle’sAnthropology, Cambridge: Cambridge University Press.
• Korobili, G. and R. Lo Presti (eds.), 2021,Nutrition andNutritive Soul in Aristotle and Aristotelianism, Berlin: DeGruyter.
• Kullmann, W., 1974,Wissenschaft und Methode, Berlin:Walter de Gruyter.
• Kullmann, W. and Föllinger, S. (eds.), 1997,Aristotelische Biologie, Stuttgart: Franz Steiner.
• Labbarrière, J-L., 2004,Language, vie politiques etmouvement des animaux: Études aristotéliciennes,Paris: Librairie Philosophique J. Vrin.
• Lennox, J., 1990, “Notes on David Charles onHA,” in Devereux & Pellegrin 1990, pp.169–183.
• –––, 2001b,Aristotle’s Philosophy ofBiology: Studies in the Origins of Life Science, Cambridge:Cambridge University Press.
• –––, 2001c, “Aristotle on the Unity andDisunity of Science,”International Studies in Philosophy ofScience, 15 (2): 133–144.
• –––, 2005, “Getting a Science Going:Aristotle on Entry Level Kinds,” in Wolters & Carrier 2005,pp. 87–100.
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• –––, 2011, “Aristotle on Norms ofInquiry,”HOPOS: The Journal of the International Societyfor the History of Philosophy of Science, 1: 23–46.
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• –––, 2020, “Aristotle on the Unity of theNutritive and Reproductive Functions”,Phronesis,65(4): 414–466. (Co–authored with Cameron Coates)
• –––, 2021, “Biology and Cosmology inAristotle”, inCosmology and Biology in Ancient Philosophy:From Thales to Avicenna, R. Salles (ed.), Cambridge: CambridgeUniversity Press, pp. 109–130.
• –––, 2021,Aristotle on Inquiry: EroteticFrameworks and Domain Specific Norms, Cambridge: CambridgeUniversity Press.
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• Leroi, A. M., 2014,The Lagoon: How Aristotle InventedScience, London: Bloomsbury Circus.
• Lesher, J. (ed.), 2010,From Inquiry to DemonstrativeKnowledge: New Essays on Aristotle’s Posterior Analytics,Kelowna BC: Academic Printing and Publishing.
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• –––, 2010b, “Aristotle’s SyllogisticModel of Knowledge and the Biological Sciences: Demonstrating NaturalProcesses,” in Lesher 2010, pp. 31–60.
• –––, 2010c, “Nature as a goodHouse-keeper: Secondary Teleology and Material Necessity inAristotle’s Biology”,Apeiron, 43(4):117–142.
• –––, 2017,From Natural Character to MoralVirtue in Aristotle, Oxford: Oxford University Press.
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• Lloyd, G. E. R., 1987, “Empirical research inAristotle’s biology,” in Gotthelf & Lennox 1987, pp.53–64.
• –––, 1990, “Aristotle’s zoology andhis metaphysics. Thestatus quaestionis. A critical review ofsome recent theories,” in Devereux & Pellegrin 1990, pp.7–36.
• –––, 1996,Aristotelian Explorations,Cambridge: Cambridge University Press.
• Marcos, A., 1996,Aristóteles y Otros Animales,Barcelona: Promociones y Publicaciones Universitarias.
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• Owen, R., 1992,The Hunterian Lectures in Comparative Anatomy(May and June 1837), Phillip Reid Sloan (ed.), Chicago:University of Chicago Press.
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