Aristotle the philosopher of natureDavid Furley1THE TREATISES ON NATUREThe subject-matter of the present chapter is what Aristotle has to say aboutthe natural world—the subject that in classical Greek is most accuratelyrendered as
ta physika. But of course this includes many topics that wouldnot now count as natural science—indeed Aristotle’s own book called
Physics contains discussions that according to twentieth-century categoriesbelong rather to philosophy or metaphysics. Book 1 criticizes the views ofAristotle’s predecessors on the first principles of natural objects, anddefends his own view that they are three—matter, form, and privation.Book 2 analyses the kind of explanation that is to be expected of thenatural philosopher, introducing the doctrine of ‘the four causes’. The thirdbook deals with motion and change, and infinity; the fourth with place,void and time. The second quartet of books seems to form a separate entity—or perhaps two. Books 5, 6 and 8 are sometimes referred to bycommentators under a separate title:
On Change (
kinêsis—the word maydenote motion or change in general). Book 5 analyses concepts essential tothe study of motion, book 6 deals with continuity, Book 8 argues for theeternity of motion and an eternal mover. Book 7 (part of which has beentransmitted in two versions) perhaps contains a preliminary version ofBook 8.In the traditional ordering of Aristotle’s works,
Physics is followed bythree theoretical treatises concerned with different aspects of the cosmos:
On the Heavens, On Generation and Corruption, and
Meteorologica.After a short essay
On the Cosmos, generally and rightly held to bespurious, these are followed by a sequence of works on biology, whichconstitutes one fourth of the surviving Corpus Aristotelicum. First comesthe treatise
On the Soul (the principle of life), and a collection of relatedshort essays concerning sensation, memory, sleep, dreams, etc., known asthe
Parva Naturalia.Then follow the three principal works of zoology:
History of Animals (
Zoological Researches would be a more appropriatemodern title),
Parts of Animals, and
Generation of Animals. (Thetraditional Corpus contains also a number of works on the natural worldnow held to be spurious:
On Colours, On Things Heard,Physiognomonics, On Plants, On Marvellous Things Heard, Mechanics,and
Problems.)
2ARISTOTLE’S SCIENTIFIC METHODS IN POSTERIOR ANALYTICS AND ELSEWHEREBefore entering upon a discussion of Aristotle’s researches into the naturalworld, something must be said about the book in which he theorizes aboutscientific proof—the
Posterior Analytics.<sup>1</sup>The book sets out a system of proof by syllogisms. We have scientificunderstanding of something, says Aristotle, ‘when we believe we know thecause (the
aitia)<sup>2</sup> of the thing’s being the case—know that it
is the cause ofit—and that it could not be otherwise’ (1.2, 71b10–12). From premissesthat are known to be true, the scientific theorist draws a conclusion that isthen also known to be true because it follows necessarily from thepremisses. If the argument is to qualify as part of a science
(epistêmê), itspremisses must have certain qualities: they must be ‘true and primitive andimmediate and more familiar than and prior to and explanatory of theconclusion’ (1.2, 71b22–24, tr. Barnes).Now when one turns to the treatises in which Aristotle sets out hisphilosophy of nature (the treatises listed above in section 1), it is at onceobvious that they do not even attempt to meet these conditions. They are,in general, inquiries, or the records of inquiries, rather than proofs. Theydo not confine themselves to necessary truths, which cannot be otherwise.In many cases, particularly in the biological works, they start frompropositions based on observation. They do not proceed by syllogisticproofs alone.It is clear that we are dealing with two different phases in thepresentation of science, and it is important that this be recognized if thereader is not to be disappointed by the apparent difference between theideal set out in the
Analytics and the more dialectical nature of the othertreatises. The
Posterior Analytics are generally held to describe the way inwhich a completed science should ideally be presented; the treatises on thenatural world present the inquiries or researches that are preliminary to thefinished product. ‘In a perfect Aristotelian world, the material gathered inthe
Corpus will be systematically presented; and the logical pattern willfollow the pattern of the
Posterior Analytics’ (Barnes [1.28], p. x).It should be added that the pattern of the Analytics evidently suits themathematical sciences rather than biology, and Aristotle would bein difficulties if he confined his biology to the knowledge that could satisfyexacting demands for necessary truths and syllogistic proof.In the two treatises (
Physics and
Generation and Corruption) that dealwith the concepts most fundamental to our study of the natural world,Aristotle uses methods that are based neither on the scientific syllogism nordirectly on empirical studies of natural phenomena. Most typically, hestarts from the views expressed by others—by his philosophicalpredecessors, or by educated and thoughtful ordinary men in general.<sup>3</sup>For example, in book 4 of the
Physics he analyses the concept of place.We should assume, he says (4.4, 210a32), whatever is rightly believed tobelong to it essentially: i.e. that it is the first thing surrounding that whoseplace it is, that it is not a part of the thing, that it is neither bigger norsmaller than it; and that it is detachable from its content when the latterchanges place. It is only because of locomotion, he adds, that we enquireabout place. The object of the enquiry is to determine what place is in sucha way that the problems are solved and the beliefs about its properties areshown to be true, and to show the reasons for the difficult problems about it.The first of Aristotle’s statements about place—namely that it‘surrounds’
(periechein) its contents—turns out to be highly significant.This at once distinguishes ‘place’ from ‘space’; Aristotle’s place is a surface—the inner surface of a container that is in contact with the outer surface ofthe contents. Thus place is not measured by its volume, as space is, or asspace would be measured if Aristotle allowed its existence. In fact, hedenies it: it is not necessary, he claims, for the analysis of locomotion,because the concept of place will supply all that is needed (and he findsother problems with the idea of space).It follows, in Aristotle’s view, that there can be no such thing as thevoid. The void could only be an empty place: but place is a container, anda container is nothing if it contains nothing. When something changesplace, its former place is occupied
pari passu by something else, or else theformer container collapses on to itself as an empty bag does.In this analysis there are no experiments, no measurements, and noobservations other than those of ordinary everyday experience. What wehave is a study of descriptions of motion, and of the assumptionsunderlying these descriptions. We have also an exhibition of the problemsarising from alternative and incompatible descriptions in terms of spacerather than place.There is a somewhat similar but more far-reaching conceptual analysis inbook 1 of the
Physics. It begins by asking: what are the
principles ofnature? That is to say, what are the things that are essential to the existenceof any natural object? To find the principles, we have to start with what isfamiliar to us, because the principles themselves are not accessible directlyto our minds, nor universally agreed. It is not principles that we are directlyacquainted with, but the changing compounds of the natural world.After a criticism of the ideas of earlier philosophers of nature about theprinciples, Aristotle continues with reflections on our common notionsabout the essential features of
change, since change is a necessary feature ofeverything in the sublunary natural world. Change takes place betweenopposites: things are said to change from hot to cold, for example, or fromdry to wet, or from unmusical to musical. So opposites must be among theprinciples. But it is false to say that
hot changes to
cold: it is not theopposites themselves that change, but something that is characterized firstby one opposite, then the other (or if not from one extreme to the other,from one position on the continuum between the two to another position
in the direction of the other). What, then, is the ‘something’, thesubstratum, presupposed by such change?Aristotle’s answer is ‘matter’
(hylê). His concept of matter is one thatwould be thought of now as belonging to metaphysics rather than tophysics. Matter is an abstraction: it is arrived at, in thought only, bystripping away from a physical object all the attributes that belong to itsform. It never exists in separation from all attributes. The simplest kind ofobject with substantial existence in Aristotle’s hierarchy of existent thingsis a piece of one of the four elements: but any such piece is analysable intheory into matter and certain qualities that give it form.In the sublunary world, as opposed to the heavens, everything that existsis liable to change, from a quality to its opposite, from a given size to alarger or smaller one, or from being what it is to being something else (forexample from being a table to being a heap of firewood, from beingfirewood to being smoke and ash, etc.). What underlies physical change ismatter: matter has the
potentiality for losing one form and taking on another.A favourite example of physical change in Aristotle’s works is themaking of a piece of sculpture. An amount of bronze or stone is thematter: it has the potentiality for becoming an image of a man, and thesculptor gives it that form in actuality. But this is rather too static ananalysis: at each stage of the process of making the statue, the material inits penultimate state is matter (potentiality) for the actuality of the nextstage. Matter and form, and potentiality and actuality, are pairs of relativeterms.The elements themselves, better named ‘the primary bodies’—earth,water, air, and fire—have the potentiality for changing into each other. Forexample water has the potentiality for vaporizing into ‘air’ or forsolidifying into ‘earth’—the names themselves in Aristotelian usage eachdenote a range of solid, liquid, gaseous, and fiery substances.<sup>4</sup>
3ARISTOTLE’S WORLD PICTUREWe shall begin with an outline of Aristotle’s picture of the natural world asa whole, contrasting it with others of the classical period, and continuewith comments on his contribution to each of the major fields, fromastronomy to biology.The general character of Aristotle’s interpretation of the natural world isdetermined primarily by two theses: that the cosmos had no beginning andwill have no end in time, and that it is a finite whole that exhausts thecontents of the universe.The first main point—that the cosmos is sempiternal—is argued in book8 of the
Physics. The first premiss is that there can be no time withoutchange: change is necessary, if parts of time are to be distinguished fromeach other. But according to Aristotle’s analysis of change, there can be no
first change, and correspondingly no
last change. It follows that bothchange and time are eternal (
Physics 8.1). Further argument (in
Physics 8.6) shows that if change is to be eternal, there must be both somethingeternal that causes change (we shall return to this all-important being insection 7), and something eternal in which this change occurs. This latterbeing is the ‘first heaven’, the sphere of the fixed stars. Since the rest of thecosmos is determined in its essentials by the motions of the heavens, thewhole cosmic order is also eternal.These claims (defended, of course, by arguments to which this baresummary does no justice) distinguish Aristotle from all major philosophersof the classical period, with the possible exception of Heraclitus.Anaxagoras held that the cosmos emerged from a primitive mixture of allits contents; Empedocles that it grows from unity, passes through a periodof plurality, and returns to unity, in repeating cycles; the Atomists arguedfor a plurality of cosmoi, each with a finite lifetime; Plato maintained thatthe single cosmos is indeed eternal, but he wrote (in the
Timaeus) adescription of its creation at a particular point in time, which Aristotle atleast believed was to be taken literally; the Stoics returned to a cyclictheory.The second of these claims—that the universe is finite—follows from aset of prior assumptions and arguments. In
Physics book 4, Aristotleargues that there can be no such thing as a vacuum anywhere in theuniverse, and hence that there cannot be an infinitely extended vacuum.What people mean when they talk about a vacuum or void, as Leucippusand Democritus did, is an empty
place. But Aristotle produced argumentsto show that there can be no such thing. The place of a thing is its
container, or rather the inner boundaries of its container. According to ourexperience, when we try to empty a container, either the contents arereplaced instantly by something else (usually air), or the container collapsesupon itself. In either case we have no empty place. A place is always theplace of something or other. It follows from this that there can be no voidplace within the cosmos, and it follows from Aristotle’s theory of themotions of the elements (which we shall examine shortly) that there can beno place outside the cosmos, since all of the body in the universe isconcentrated in the cosmos.In order to show that the universe is finite, then, it remains to show thatthere cannot be an infinitely extended
body or plurality of bodies.This Aristotle aims to do in
On the Heavens 1.5–7. He begins with anargument concerned with the ‘first body’—i.e. the body of which thesphere of the fixed stars is composed (for which see section 5). Like mostGreeks of the classical period Aristotle believed the earth to be stationaryat the centre of the spherical heavens. The fact that it was stationaryseemed to be given by experience: once that thesis was accepted, it followedthat the heavenly bodies move around the earth. Before Aristotle’s time, ithad been established that there was a difference in the motions of theheavenly bodies: the stars appear to move in concert without changingtheir relative positions, while the sun, moon, and five ‘wanderers’
(planêtai) move around the earth in orbits different from each other andfrom the ‘fixed’ stars.The appearance of the fixed stars suggests that they are placed on asphere that rotates as a whole on its axis, with the earth at its centre. Weobserve that this sphere completes one revolution in a day. If it wereinfinite in radius, each radius drawn from the centre would sweep aninfinitely large distance in every segment traversed. But that is impossible:it is not possible to traverse an infinite distance, since the infinite is ‘that ofwhich there is always more beyond’ (
Physics 3.6, 207a1).In dealing with the four sublunary elements—earth, water, air, and fire—Aristotle takes as given his theory of their natural places and naturalmotions.
All earth tends to move towards a single centre,
all fire to a singlecircumference, and the other two to intermediate positions. Consequentlythere cannot be any portion of the four elements, either simple or incompounds, outside the boundary of the sphere of the stars. But neithercan there be any empty place outside this sphere, since, as Aristotle hasargued, all place must be the place of something. Hence the universe (notmerely the cosmos bounded by the starry sphere) is finite.
4THE NATURAL MOTIONS OF THE ELEMENTSAristotle’s theory of the elements is defended in detail in his
On theHeavens; books 3 and 4 deal with the four elements that had becometraditional since the time of Empedocles—earth, water, air, and fire—whilebooks 1 and 2 introduce what Aristotle calls ‘the first element’ or ‘the firstbody’ and subsequent writers called ‘aether’, the element of which theheavens are composed.Observation of the natural world suggests a distinction between forcedand natural motions: a stone can be thrown upwards, but falls downwardsif not prevented; fire and hot vapours rise upwards unless confined bysomething above them. Aristotle systematizes these simple observationswith the help of the geometrical picture of the cosmos described in the lastsection. ‘Downwards’ is defined as ‘in a straight line towards the centre ofthe universe’; ‘upwards’ is the contrary direction, away from the centre.These two rectilinear movements are contrasted with motion in a circlearound the centre of the universe.The rectilinear motions are natural to the elements contained within thesphere of the heavens—commonly called the ‘sublunary’ elements, since themoon is the innermost of the heavenly bodies. These motions are definedaccording to the ‘natural place’ of each element. Each element has anatural tendency to seek its natural place, if displaced from it. Earth andwater move naturally downwards, towards the centre; fire and air upwards.The tendency to move in these directions is what is meant by ‘weight’ and‘lightness’ respectively—thus lightness is not a relative property but anabsolute one. Earth has more weight than water, and fire has morelightness than air.It is important to note that Aristotle takes the centre, and therefore theelementary motions, to be defined by the spherical shape of the universe asa whole, not by the shape of the cosmos. Later philosophers abandonedAristotle’s notion that the sphere of the stars has nothing whatever outsideit, and posited an infinite volume of empty space around the cosmos. Insuch a cosmology no centre of the universe as such could be defined, andAristotle’s theory of natural motion had to be changed. To deal with thisproblem, the Stoics made the highly significant claim that the body of thecosmos is naturally attracted towards
its own centre. This theory ofattraction began to make clear what Aristotle never elucidated: what is the
cause of the natural motions of the elements? We shall discuss this problemlater (section 7).
5THE STRUCTURE OF THE HEAVENSThe natural motions of the four sublunary elements were rectilinear. But theheavenly bodies move in circular orbits, carried around on the surfaces ofrotating spheres (we shall describe the arrangement of the spheres in thenext sections). But physical spheres must have physical
body. So Aristotleis faced with the question: what are the heavenly spheres made of? Theycan hardly be made of any of the four elements which have rectilinearmotions. The motion of the heavens, according to Aristotle’s view in the
On the Heavens, requires us to posit a fifth element whose natural motionis not rectilinear but circular. Since he regards it as superior, in more thanone sense, to the other four elements, he names it ‘the first body’. Butalthough he made a technical term out of it, the idea of a special element inthe heavens was not his alone, and others referred to it with the old word‘aether’—originally used for the bright sky above the misty air. Forconvenience I shall adopt this term for Aristotle’s ‘first body’.We can distinguish more than one argument for the existence of aether.<sup>5</sup>The main argument in Aristotle’s
On the Heavens is the argument frommotion that we have just described. A second argument is also found there:it may be called the argument from incorruptibility. Earth, water, air, andfire are perishable in that they are all liable to change into each other. Butthe heavens are eternal: they must therefore be made of a different element.This argument can be found, in rather disguised form, in Aristotle’s
On theHeavens 1.3 (there is a very similar statement of it in
Meteorologica 1.3). Itis disguised in this sense. Aristotle first states the argument for the existenceof what he calls ‘the first body’ from the need for a body endowed withnatural circular motion. He then
deduces that it must be ungenerated,indestructible, and unchangeable. His reasoning is that all generation takesplace between opposites, opposites have opposed motions, and there is noopposite to circular motion (it is not clear why he dismisses the notion thatclockwise has its opposite in anticlockwise—if we may use such modernterms). Hence, the body that moves in a circle is not liable to generationand destruction. He continues the chapter with some less technicalthoughts about this element. These include the idea that ‘according to therecords handed down from generation to generation, we find no trace ofchange either in the whole of the outermost heaven or in any of its properparts’. Moreover, he says, the name ‘aether’ was given to the first body ‘bythe ancients…choosing its title from the fact that it “runs
always”
(aeithein) and eternally’ (270b13–24). It is not, in other words,
circular motionthat is the primary characteristic of this element, but
eternal motion. Theseideas at least produce the materials out of which the incorruptibilityargument for the existence of the fifth body can be constructed, and theetymology suggests that in Aristotle’s view this might have been the earliestargument for its existence.There are indications that Aristotle rather tentatively gave a role toaether in the sublunary world as well as in the heavens. Cicero knewsomething to this effect, from his acquaintance with some of the works ofAristotle that are now lost:He [sc. Aristotle] thinks there is a certain fifth nature, of which mindis made; for thinking, foreseeing, learning, teaching, making adiscovery, holding so much in the memory—all these and more,loving, hating, feeling pain and joy—such things as these, he believes,do not belong to any one of the four elements. He introduces a fifthkind, without a name, and thus calls the mind itself
‘endelecheia’,using a new name—as it were, a certain continual, eternal motion.(Cicero
Tusculan Disputations 1.10.22)It is hardly likely that Aristotle
identified the mind with aether, but it ispossible that at some time he wrote of the soul, or some of its faculties, asbeing based in an element different from the usual four. There is someconfirmation of this in his own more cautious words:Now it is true that the power of all kinds of soul seems to have aconnexion with a matter different from and more divine than the socalledelements; but as one soul differs from another in honourand dishonour, so also the nature of the corresponding matter differs.All have in their semen that which causes it to be productive; I meanwhat is called vital heat. This is not fire or any such power, but it isthe breath included in the semen and the foam-like, and the naturalprinciple in breath, being analogous to the element of the stars.(Aristotle
Generation of Animals 2.3, 736b29–737a1)The evaluative strain in this quotation is significant. The extra element iscalled ‘divine’ and is associated with the ranking in ‘honour’ of the soulthat is based on it—this refers, no doubt, to a
scala naturae which putsman, the rational animal, at the top and grades the lower animalsaccording to their faculties.<sup>6</sup> Aether is not merely the element endowedwith the natural faculty of moving in a circle, which is the main emphasisin the
On the Heavens. It is also eternal, and therefore divine, and free fromthe corruption of the earthly elements.Aristotle was committed to a dualism as sharp as Plato’s distinctionbetween the intelligible and unchanging Forms and the perceptible andperishable material world. The heavens are the realm of a matter thatmoves eternally in circles, is incorruptible, unmixed, divine. With thepossible limited exception of the material base of the animal soul,everything in the cosmos inside the sphere of the moon—the sublunaryworld—is made of different materials, all of them rectilinear and thereforefinite in motion, perishable, liable to mixture and interchange amongthemselves. This was a dualism that lasted, notoriously, until the time ofGalileo and Kepler, when the telescope revealed the moon to be not so verydifferent from the earth, and the idea of circular motion at last released itspowerful grip on the astronomers’ imagination.
6THE BORROWED ASTRONOMYPlato (said Sosigenes) set this problem for students ofastronomy: ‘By the assumption of what uniform and orderedmotions can the phenomena concerning the motions of theplanets be saved?’(Simplicius
De caelo 488.21)Aristotle followed Plato in analysing the motions of the heavenly bodiesentirely into circles with the earth as centre. The motions of the ‘fixed’stars, during the time they are visible at night to an observer on the earth,are arcs of circles, and they are assumed to complete their circular paths inthe daytime, when they are invisible. But the planetary bodies, includingthe sun and the moon, appear to ‘wander’ (in Greek,
planân) withreference to the fixed stars in the course of a year. In fact, however, they donot
wander, Plato had said; Aristotle agreed that their paths could beanalysed as being circular, but adopted a much more complex account ofthe circles than Plato’s.The basis for his account of the heavens was the work of twocontemporary astronomers: Eudoxus of Cnidos and Callippus of Cyzicus.<sup>7</sup>They worked out what was basically a geometrical model of the paths ofthe heavenly bodies. Aristotle added what he considered to be necessary fora physical model (to be described in the next section).The essence of the geometrical model is as follows. The fixed stars areassumed to be set rigidly in the outermost sphere of the heavens, whichturns at a constant speed about its north/south axis once a day. Inside theoutermost sphere are seven sets of concentric spheres, one set for each ofthe five known planets and the sun and the moon. The innermost sphere ofeach set carries the planetary body on its equator (this applies to thegeometrical account: the physical model is still more complex). Theoutermost sphere of each set moves on the same axis and with the samedirection and speed as the sphere of the fixed stars. It carries with it thepoles of a second sphere, concentric with the first, rotating about its own,different axis at its own constant speed. The axis of the second sphere isinclined to that of the first so that its equator, as it rotates, passes throughthe middle of the signs of the zodiac (i.e. along the ecliptic circle). Thesecond sphere of each of the planetary bodies has the same orientationrelative to the fixed stars and the same direction of rotation as each other;they differ in the time taken to complete a rotation.But the planetary bodies are observed to deviate from regular motion onthe ecliptic circle: they do not keep to the same path. To account for thedifferences, Eudoxus posited a third and fourth sphere for each planet,nested inside the first two, rotating on different axes and completing theirrotation in different times. The planet is assumed to lie on the equator ofthe fourth, innermost sphere. The third and fourth spheres are so arrangedthat the planet follows a path (relative to the ecliptic) known as a‘hippopede’ or ‘horse-fetter’, roughly equivalent to a figure 8.<sup>8</sup>All that is visible to the observer, of course, is the light of the heavenlybodies: the spheres are invisible. The visible heavenly bodies themselves donot move at all; they are carried around by the motion of the sphere inwhich they are set.The seven sets of spheres are nested inside each other, in the orderSaturn, Jupiter, Mars, Venus, Mercury, sun, moon.<sup>9</sup> In Eudoxus’ scheme,there are no eccentric spheres and no epicycles, as in later astronomicaltheories. Consequently it was assumed that all the heavenly bodies remainat a constant distance from the earth: it is a weakness in the system that ithas no way of explaining differences in the brightness of the planets atdifferent times.This, then, was the astronomical model taken over by Aristotle. Heacknowledges his debt to the mathematicians, but there are numerousobscurities in his account which raise doubts about the depth of hisunderstanding of contemporary astronomy.<sup>10</sup> What is clear is that heconstructed a physical description of the heavens, in which the sphereswere not geometrical postulates but material bodies, and the mostimportant element in this body of theory is his examination of the causesof the motions of the spheres.
7FROM ASTRONOMY TO PHYSICS AND THEOLOGYThe astronomical model, as we have seen, used the motion of the sphere ofthe fixed stars as the base on which the other motions were overlaid. Forthe construction of a physical theory, this created a difficulty concerningthe motions of all the planetary bodies except the outermost one, since thesets of planetary spheres are implanted in each other. Jupiter’s set, to takean example, is inside the set of Saturn’s spheres. But in the astronomicalmodel the motion of the innermost of Saturn’s spheres—the sphere thatcarries Saturn on its equator—is obviously not identical with that of thesphere of fixed stars; its function is precisely to justify Saturn’s deviationfrom that motion. To preserve the geometrician’s scheme, however,Jupiter’s outermost sphere must move with the motion of the fixed stars.Consequently the physical theory must return to this base, by interpolatinga set of spheres whose motions
cancel out the special motions of Saturn.Let S1, S2, S3, S4 be the spheres that explain Saturn’s motions; S4 is theone that carries Saturn. Then Aristotle postulates, inside S4, a sphere S−4,which rotates on the same axis and at the same speed as S4, but in thereverse direction. Its motion is thus identical with that of S3. He postulatesS−3, and S−2, in similar fashion. Now S−2 has the same motion as S1—i.e.the motion of the fixed stars. The first of Jupiter’s spheres, J1, has its polesfixed inside the sphere S−2.For some reason, a
complete set of spheres, starting from the motion ofthe fixed stars, is postulated for each planetary body. The point is this. Theoutermost sphere belonging to Jupiter, J1, moves with the motion of thefixed stars. But so does its outer neighbour, S−2. So one of these isredundant. The same applies to all of the inner planetary bodies. It is notclear why Aristotle did not economize in this way.In fact, Aristotle took over Callippus’ modifications of the Eudoxansystem, and held to the thesis of a complete and separate set of spheres foreach planetary body. They can be listed as follows (positive followed bycounteracting spheres):Saturn 4 + 3Jupiter 4 + 3Mars 5 + 4Mercury 5 + 4Venus 5 + 4Sun 5 + 4Moon 5No counteracting spheres are required for the moon, since there are noheavenly bodies beneath it; so the total is 55. It seems that the outermostsphere of Saturn is identical with the sphere of the fixed stars, which is notcounted separately.<sup>11</sup>But before leaving the subject of the heavens, we must raise the questionthat from some points of view appears to be the most important of all:what is the
cause of the motion of the spheres? Since Aristotle concludesthat circular motion is natural to the element of which the heavenly spheresare made, it might seem that there is no further cause to be specified: itmight be the case that it is just a fact of nature that this element moves incircles, unless something prevents it, and the position of the poles of eachsphere and their relation to each other determines what particular circularorbit is traced out by each particular bit of the aetherial element. Since in
On the Heavens he attacks Plato's theory that the heavens are moved bytheir soul, and is silent (in general) about the existence of an externalmover, it is tempting to think that in the period when that work was puttogether Aristotle held a mechanical theory of the motions of theheavens.<sup>12</sup> The whole system of cosmic motions, both in the heavens and inthe sublunary world, might then be held to work on the same mechanicalprinciple—the natural self-motion of the five elements. This would fit wellenough with one interpretation of Aristotle's well known definition of'nature', in
Physics 2.1, as an internal principle of motion and rest.But it can hardly be so simple. Change in general, including locomotion,is analysed by Aristotle as the actualization of a potency: he insists thatthere must be some kind of agent that is actual in the required sense, andsomething that is not yet but can become actual in this sense; and thatthese two must be distinct. They may be parts or aspects of the samesubstance, but they must be distinct from each other. The nearest to anexample of a self-mover is an animal: what moves it is its soul, what ismoved is its body. But he contrasts this example explicitly with themotions of the elements: the elements cannot be self-movers even in thissense, because if they were, they could (like animals) stop themselves aswell as put themselves into motion.Aristotle never makes it entirely clear what causes the natural fall ofearth or the natural rise of fire; but in the last chapters of
Metaphysics 12(Lambda) he introduces the external mover of the heavenly spheres. God istheir mover, himself unmoved whether by himself or any other being. ThisUnmoved Mover is pure actuality, with no potentiality for internal change.As such, he is the guarantor of the eternity of the motions of the heavens.In the relation between mover and moved, the motion is often broughtabout in some way that necessitates a motion performed by the
mover. forexample an artist or craftsman produces something out of the availablematerials by
doing something to them. The prime example of a motion thatis
not brought about in this way is one that is caused by the thought anddesire of the moved object—that is to say, when the moved objectconceives of the actuality represented by the mover as good andconsequently desirable. This is, remarkably, the model chosen by Aristotlefor the motions of the heavens.The model entails a degree of animism in his cosmology: the heavenlyspheres, if they are to be capable of thought and desire, must possess souls.Aristotle presents his theology in a notably impressionistic way. It seems (in
Metaphysics 12.8) that each of the fifty-five spheres must have its ownmover; yet we are not told how such beings can be individuated, and insome of the few paragraphs devoted to this all-important topic it appearsthat a single unmoved mover is envisaged. At least it is clear that if there isa plurality it is an organized plurality: Aristotle ends the book with aquotation from Homer: ‘The rule of many is not good: let there be oneruler.’<sup>13</sup>Aristotle’s cosmic deities are remarkably non-providential: their functionin his system is to sustain the motions of the cosmos eternally. They haveno hand in the creation of the cosmos, since it had no creation but hasexisted in its present form from all eternity; and they have apparently nothought for the welfare of any particular species or for the whole, except inso far as the eternal survival of the whole system and of all its naturalkinds is a matter of concern.In the surviving works of Aristotle there is astonishingly little on thissubject, which one might have expected to be crucial. In the theologicalchapters of
Metaphysics 12 (Lambda), he speaks of God in the singular,but introduces plural gods as movers of the spheres without clarifying thechange from singular to plural. He describes the activity of the ‘first mover’in strikingly reverential words:On such a principle, then, depend the heavens and the world ofnature. And its life is such as the best which we enjoy, and enjoy butfor a short time. For it is ever in this state (which we cannot be) sinceits actuality is also pleasure. And thought in itself deals with thatwhich is best in itself…. If, then, God is always in that good state inwhich we sometimes are, this compels our wonder; and if in a better,this compels it yet more. And God is in a better state. And life alsobelongs to God; for the actuality of thought is life, and God is thatactuality.(Aristotle
Metaphysics 12.7, 1072b14–29, tr. Ross)But the content of God’s thought is never described, and remains a matterof controversy.<sup>14</sup>
8MATTER AND ITS QUALITIES IN THE SUBLUNARY WORLDAt the end of the fourth century, Democritus put forward the theory ofatoms. All of the ‘being’ in the universe, in his view, took the form ofunbreakably solid pieces of matter, invisibly small individually but capableof combining temporarily into compounds large enough to be perceived.The only other item in the universe, endowed with a kind of being butsometimes also contrasted with atoms and characterized as ‘not-being’,was void space—itself absolutely without any properties except spatialextension. All the objects in the familiar world perceived by us werecomposed of atoms with some quantity of void interspersed between them.The perceptible qualities of things were explained as the outcome of thenumber and shapes of the component atoms, the quantity of void betweenthem, and their motions in the void.Plato, in his cosmological dialogue
Timaeus, rejected this simple ‘bottomup’ type of explanation, although he did not entirely abandon the conceptof atoms. In his theory, the beings primarily responsible for thecharacteristics of the physical world are the immaterial Forms, accessible tothe mind rather than directly to the senses. Physical objects derive theirproperties from the Forms that they ‘partake in’ or ‘imitate’. The propertiesof perceptible bodies are, however, related to the nature of the particleswhich they contain. Plato describes the mathematical structure of particlesof the four traditional elements, earth, water, air, and fire. The quality ofheat, for example, is related to the sharply angled pyramidal shape ofparticles of fire. But Plato’s particle theory is different from Democritus’atomism in that his particles are not described as having solidity orresistance. They may be regarded as a conceptual analysis of the qualitiesassociated with them, rather than as results of a breakdown of a compoundinto material components.Aristotle’s theory was in more complete contrast with Democritus thanPlato’s, in that he abandoned corpuscles altogether in favour of acontinuous theory of matter. He himself analyses the argument which, hesays, induced Democritus to introduce ‘indivisible magnitudes’ into histheory. It was a response to the paradoxes of the Eleatic Zeno, and wentlike this, in brief (
De gen. et corr. 1.2, 316a11 ff.). Suppose that there are
no indivisible magnitudes: then every magnitude would be divisible adinfinitum. Suppose such a division ad infinitum were completed: then onemust be left either (a) with a collection of undivided magnitudes (whichcontradicts the hypothesis that every magnitude is divisible), or (b) with acollection of parts with no magnitude (which could never be put togetherto make a magnitude), or (c) with nothing at all. Hence, Democritusconcluded, there must be indivisible magnitudes. Aristotle’s response wasthat every magnitude is indeed divisible every-where, but not everywhere
simultaneously. Hence there are no indivisible magnitudes, but in dividingone never arrives at an infinite collection of simultaneous parts.It would be a comparatively easy business to describe his theory if he hadmade it clear what exactly composes his continuum. Difficulties arisebecause he fails to make clear whether or not we are to consider thecontinuum as being composed of ‘prime matter’, without any qualitiesbeyond those of three-dimensional spatial extension and resistance, or asbeing invariably endowed with further qualities.There is no doubt that he adopted the four elements first clearlyidentified by Empedocles, and taken over by Plato: earth, water, air, andfire.<sup>15</sup> He rejected Plato’s theory that the four differ from each otherbecause of the mathematical shape of their particles: instead he allocated toeach of them (in addition to natural motion, upwards or downwards) apair of the primary qualities, hot, cold, dry, and wet. Thus earth is cold anddry, water cold and wet, air warm and wet, fire warm and dry. UnlikeEmpedocles, he held that that the elements change into each other byexchanging qualities. For example, evaporation is analysed as thereplacement of water’s coldness by warmth.But water is not
simply coldness and wetness: cold and wet are qualitiesthat give form to a substratum: water is
something that is cold and wet.The ‘something’ that underlies the qualities is barely described by Aristotle;hence there arises a controversy as to whether or not he had a conception of‘prime matter’. His theory of elementary change does not require a stage atwhich there exists prime matter without any qualities: what changes intoair, to continue with the example of evaporation, is water, and it changesdirectly, with no intermediate stage. But each of the four elements hasthree-dimensional extension and resistance, and these properties remain inplace (in some sense, if not exactly) when a given quantity of waterchanges into air. If that is enough to constitute a theory of prime matter, thenit seems undeniable that Aristotle held such a theory. But his account ofchange requires that there never exists an instance of prime matter withoutqualities.The four elements are given the familiar names of earth, water, air, andfire, but that is misleadingly simple. The element ‘earth’ gathers ineverything that is solid, water everything that is fluid or pliable, aireverything that is misty or gaseous. Fire is to some extent
sui generis, anddoes not fit well into this scheme.
9FOUR LEVELS OF MATERIAL BEING1 The four elements (‘primary bodies’)2 Homoiomerous bodies3 Anhomoiomerous parts4 OrganismsThe main point of this classification is to distinguish (2) from (3), and thedistinction depends on whether the part
(meros) has the same name as thewhole. If we take a part of a substance such as blood or bone or skin, eachof them has the same name as the whole: a bit of bone is bone, and so on.At the next level, the same is not true: a bit of a hand is not a hand (nor‘hand’), nor a bit of a face a face (or ‘face’). ‘Anhomoiomerous’ means‘having parts that are dissimilar’. The anhomoiomerous parts are made ofthe homoiomerous tissues: a hand is made of skin, bone, muscle, etc.This distinction serves only to distinguish level (3) from (4), not (1) from (2).Earth, water, air, and fire are homoiomerous.
10THE FORMATION OF COMPOUNDSOut of the elements, the tissues: out of these, as matter, the wholeof nature’s works. But though they are all out of these saidelements as
matter, in respect of their
real being they are[determined] by their definition.This is always clearer in higher-level things, and in general inthings that are for an end, like tools. It is clearer that a corpse isa man in name only; similarly, then, a dead man’s hand, too, isa hand in name only…; such things are less clear in the case offlesh and bone, still less in fire and water, because the finalcause is least clear here, where matter predominates.…Such parts, then [sc. the simpler elements of organiccompounds], can come-to-be by heat and cold…. But thecomplex parts composed of these—for example head, hand, foot—no one would believe to be composed in this way. Thoughcold and heat and motion are causes of bronze and silver’scoming-to-be, they are no longer the causes of a saw or a cup ora box.(Aristotle
Meteorologica 4.12, excerpted)Aristotle’s anti-reductionist stance, in strong opposition to Democritus, isclearly announced in this last chapter of book 4 of his
Meteorologica(which I take to be a genuine book serving as a bridge between his physicaland biological works).<sup>16</sup> He has given an account of the four simple bodiesand their motions; he has shown how they combine to make the next layerof his hierarchy of materials—the ‘tissues’, or ‘the homoiomerous bodies’,to use his own technical term. But he wants to make it clear that this‘bottom-up‘procedure is
not the way to analyse the physical world.Material elements are the ingredients, but they do not make the naturalcompound. Empedocles and Democritus were wrong.Much more important than the material cause is what he designates here asthe
logos, which I have translated ‘definition’ in the passage above.We shall examine this again in the next section: for the moment, twopoints must be made.First, Aristotle’s claim is that to know what a thing really is is not just toknow what it is made of, by taking it to bits, so to speak, nor just to tracethe motions that its ingredients performed in composing it, but rather toknow something about it as a present whole. In the case of an artifact, weshall want to know what it is
for, the final cause; in the case of a livingthing, we shall want to know what it
does so as to survive and reproduce.So we know about
this object (for example a saw), not when we discoverwhat are the shapes, numbers, and dispositions of its component atoms orother material ingredients (although we shall want to know
somethingabout its components), but rather when we see that it is to cut wood andunderstand how its components enable it to do that. We know about
thisobject (for example a frog) when we see where and how it gets a living andunderstand how its parts enable it to live and to reproduce.So much is an epistemological point: form, or definition (which putsform into words), takes priority over material ingredients for the purpose ofknowledge. But this is true about knowledge just because the same priorityoperates in reality. Matter-in-motion, by itself, does not make a saw or acup or a box, still less a head or a hand or a foot. The forms or kinds thatexist in nature are the primary data. As causes of the production ofindividual members of species they take priority over the earth, water, air,and fire that are used in the production. It is form that dominates.
How itdominates and operates as a cause is what we must examine.Aristotle’s theory of the roles of matter and form in the processes ofnature bears a strong resemblance to Plato’s distinction in the
Timaeusbetween Necessity and Mind. It is true that Plato locates the operation ofthese two causes in the
creation of the physical world by the CraftsmanGod, whereas Aristotle uses them to explain the continuous cycles ofcoming-to-be and passing-away. But the function of the two causes is verymuch the same in both theories. Plato’s Craftsman copies the Forms in amaterial base; he makes the best possible copies, given the limitationsimposed by the Necessity of the materials. In Aristotle’s theory, it is theforms themselves, without the designing mind of a Craftsman God, thatshape and guide the potentialities of the four simple bodies and the materialcompounds formed out of them. For Aristotle, the materials representNecessity in two guises. Materials with certain definite qualities are
necessitated by the nature of the form they are to take on—a saw-blade mustnecessarily be of metal, not wood, and a bone must be made of somethingrigid, not liquid. They are also
necessitating, in that they necessarily bringwith them the whole set of their own properties, whether or not these areall necessitated by the forms. Thus the saw’s metal is necessarily liable torust as well as being capable of being sharpened, the bone is necessarilyfragile as well as rigid, if it is not to be too ponderous.<sup>17</sup>Aristotle’s point against the Atomists is not that simple kinds of matterhave no necessitating or causative properties, but that these properties
alone cannot bring about the complex forms observed in nature. What they
can bring about is described in the fourth book of
Meteorologica, where hedistinguishes four layers of complexity of natural objects, as we have seen.The point Aristotle makes in the quotation at the beginning of this sectionis that the necessitating properties of matter become less and less dominantwith each step up through the layers. They have the greatest effect in theformation of the homoiomerous tissues from the elements. The activepowers of heat and cold in the simple bodies work on the passive qualitiesof moisture and dryness to produce compounds that differ from each otherby being, in different degrees, solidified, meltable, softenable by heat,softenable by water, flexible, squeezable, ductile, malleable, fissile,cuttable, viscous, compressible, combustible, and capable of giving offvapours (this is Aristotle’s list, in
Meteorologica 4.8, 385a12–19). Thenature of the homoiomerous bodies is determined by these properties,together with the degree of heaviness or lightness imported by theproportions of each of the simple bodies in their composition.Given the heating action of the sun, then, and the seasonal changes inthat action brought about by the sun’s motion in the ecliptic circle, we maybelieve that the continuum of the four simple bodies must be so stirred upinto qualitative interaction that many varieties of compound bodies may beformed withot the intervention of other causes. Even at this level,Aristotle’s theory is not reductionist: he did not hold that all these differentqualities were ‘nothing but’ different degrees of hot, cold, dry, and wet, northat the homoiomerous bodies are ‘nothing but’ earth, water, air, and firein different proportions. They are all to be thought of as real features of thenatural world, generated by the interactions of the simple bodies but notreducible to them.But even at this level, the generation of the complex out of the relativelysimple is rarely caused solely by matter in motion. Homoiomerous tissueslike oakwood, fishskin or cowhide are plainly enough
not brought intobeing by the action of the sun and the natural properties of the four simplebodies, and nothing else. Aristotle says no more than that the causativeaction of form is
less obvious at the lower stages, not that it is entirelyabsent.
11THE FOUR CAUSESThe four are listed in
Physics 2.3:In one way, that out of which a thing comes to be and which persists,is called a cause, for example the bronze of a statue….In another way, the form or the archetype, i.e. the definition of theessence and its genera, are called causes….Again, the primary source of the change or rest….Again, in the sense of end or that for the sake of which a thing isdone….These are traditionally referred to as the material, formal, efficient, andfinal causes. ‘The causes being four, it is the business of the student ofnature to know about all of them, and if he refers his problems back to allof them, he will assign the “why?” in the way proper to his science’(
Physics 2.7, 22–25). But there are reasons for being hesitant about theword ‘cause’ as a translation of Aristotle’s
aition or
aitia. No singletranslation is adequate for all contexts—the bronze of which a statue ismade, for instance, is not naturally called a ‘cause’ of the statue. The basicidea is to classify those items which are responsible for a thing’s being whatit is. Closest to the modern ‘cause’ is the third in Aristotle’s list, theefficient cause—the sculptor, in the case of the statue. But the bronze ofwhich it is made may well be cited as being responsible for some aspects ofits nature; so also its form, and the end or purpose for which it was made.In the last chapter of the
Meteorologica, quoted at the beginning of thelast section, Aristotle insists that it is inadequate to mention materialconstituents alone as responsible for the nature of the compound: inanything but the simplest objects in the world, form is of much greaterimportance. But form alone is still insufficient: it is necessary to specifywhatever it is that is responsible for giving
this form to
this matter—theefficient cause. And in many cases, for a full explanation we need to knowthe goal or end served by the possessor of this form in this matter. Thissimple schema dominates Aristotle’s studies of the natural world. It guideshis inquiries, and gives shape to his presentation of the results.
12ARISTOTLE’S ZOOLOGICAL WORKSThe major works are
Parts of Animals (PA), Generation of Animals (GA),and
History of Animals.The first of these provides two introductions to zoological studies.
PA 1.5 is a fluently written and rather elementary ‘protreptic’, urging studentsnot to be contemptuous of biology as opposed to ‘higher’ studies such asmetaphysics or astronomy, which deal with eternal rather than perishablethings. In the realm of biology, we have the advantage of being closer tothe subject matter, and are therefore better able to study it. Moreover, thephilosophical mind will find great satisfaction in discovering and analysingthe causes at work in plants and animals, where Nature offers much that isbeautiful to the discriminating eye.
PA 1.1 is a discussion of causes, and above all a defence of the view thatthe final cause is most prominent in the works of nature. Lacking a theoryof the evolution of species, Aristotle treats as the starting point for biologythe form of the grown specimen—the adult horse or man, the full-grownoak tree. This is in opposition to those who started from the materialelements—for example, Democritus. The first step is to understand themode of life of the animal, and to observe what it needs for survival andfor reproduction. These are the two essentials for understanding structureand behaviour. Each animal exists in a particular kind of environment, andthe nature of the environment determines what will be good for theanimal’s survival and reproductive capacity. The student of nature,therefore, will observe the animal and its parts, and decide first whatcontribution each part makes to survival and reproductive capacity. This isthe ‘cause’
for the sake of which the part exists and has the structure that itis observed to have. The student will understand the nature of the animalwhen these causes are understood.Aristotle uses the word ‘cause’
(aitia) in its usual Greek sense, as thatwhich is responsible for the phenomenon to be explained. But he does notmean to imply that the parts of animals are
caused to grow (in our sense of‘caused’) by capacities that lie in the future: the hooked beak of the(individual) hawk is not caused by its capacity, when grown, to tear up theflesh of its prey. The key to Aristotle’s teleology, in the biological realm, isthe identity of the form of the (male) parent and the offspring.<sup>18</sup> Theparental hawk (to continue the example) survived to produce offspring justbecause its beak was of a kind well adapted to its mode of life; such a beakwas an essential attribute of the form of the hawk; and this form istransmitted to the offspring. The final cause—that ‘for the sake of which’the part of the creature exists—is thus subsumed into the efficient cause.The semen of the parent carries the form of the parent and transmits it, asefficient cause in the process of generation, to the offspring.The mechanism by which this transmission of form is achieved isdescribed in detail in
Generation of Animals. Aristotle dismisses the theorythat the semen is drawn from all the parts of the parent’s body(pangenesis). That theory, which is set out in the surviving Hippocratictreatise
On Seed, and was probably also defended by Democritus, wasbased on the resemblances of children to their parents. Aristotle argues thatthis proves too much or too little. Children resemble their parents incharacteristics such as their manner of movement which is not determinedby physical structure. Moreover children sometimes resemble grandparentsor other family members, rather than parents. His own theory depends onhis metaphysical distinction between form and matter. The matter of theembryo is provided by the mother, the form by the father.The semen carries in it the ‘movements’ that will cause the parts of theembryo to grow in the proper order and form. These movements are notsimply instructions, nor an abstract design or formula: they are derivedfrom the soul of the adult parent, and they are embodied in a materialsubstance carried in the semen, called
pneuma. Pneuma, is a concept thatplays a large part in Greek physiology, from the earliest times, when it isequated more or less exactly with the breath of life. But Aristotle’s use ofthe concept is ill defined. He speaks of the ‘connate
pneuma’; it is clearlynecessary for life, and is especially associated with the faculties of soul suchas sensation and movement. It carries also the idea of vital heat. But hedoes not give it the precise and detailed description that forms animportant part of Stoic theory, and he does not explain its relation to thefour material elements. There is a single mysterious hint (
GA 2.3, 737a1,mentioned above, in section 5) that it is ‘analogous to the element of thestars’.<sup>19</sup>The
History of Animals, in ten books, has sometimes been taken toattempt a classification of animals—not by the process of ‘dichotomizing’(dividing genera progressively by two into narrower classes) practised byPlato but rejected by Aristotle—but by more complicated methods. Recentresearches, however, have shown that that the motivation of these treatisesis rather to examine the differentiae of animals (for example the shape andsize of legs, the apparatus of the senses, the modes of protection) and torelate them to the needs of the animal to get food, to ward off predators,and to bring up the next generation.<sup>20</sup>Aristotle uses the terms
genos and
eidos, which became the standardwords for what later biologists denote by ‘genus’ and ‘species’. But it isclear from examination of the texts that
genos in Aristotle can denoteclasses of varying degrees of generality, and
eidos is not always subordinateto
genos. What Aristotle seeks to do is to identify the kinds of animalsthere are, as defined by their mode of life in their environment, and topresent comparative studies of the structure and organization of their partsas they are adapted to their function. Hence the supreme importance of thefinal cause. The biologist above all seeks to explain the connection betweeneach of the characteristic actions of each animal kind, and the structure ofthe parts of the body that enable the animal to perform these actions.
13PSYCHEPsyche is usually translated by the English word ‘soul’, and it is convenientto use the word in spite of its misleading modern connotations.<sup>21</sup> Aristotletreats
the psyche as the defining principle of life: the four material elementshave no
psyche, in spite of their natural tendency to seek for their naturalplace in the cosmos; compounds of the elements have no
psyche, unlessthey possess at least the faculties of nutrition and reproduction. Aristotleconstructs a
scala naturae in which each higher step of the ladder isdistinguished by the addition of further faculties of the soul. Plants andanimals have the basic faculties of nutrition and reproduction; in additionto these, animals have sensation, although not all of them have all of thefive senses; some animals, but not all of them, have also the capacity tomove themselves; man has all of the animal faculties, with the addition ofimagination
(phantasia) and reason, which are also shared, in some smalldegree, by the higher animals.There is thus an ascending order of plant and animal species to be foundin the world. This is not, however, an order produced by evolutionaryprocesses: on the contrary, all of the species now in existence have alwaysexisted, in Aristotle’s view, and will continue to exist. We will discuss therelations between the species briefly in the next section.It is, of course, a crucial ingredient of Aristotle’s theory that the soul isnot an entity separate from the body, nor indeed separable in any wayexcept by abstraction in thought (there could be no transmigration of soulsin his theory). The soul is ‘the first actuality of a natural body that ispossessed of organs’ (
On the Soul 2.1, 412b5). If a body is to have soul, itmust have the organs that give it the potentiality of carrying out some of thefunctions of life. The soul is described as the
first actuality because it is notnecessary for the functions of the living body to be
in action to qualify thebody as ‘ensouled’. The eyes of a corpse or a statue are not alive, but theeyes of a sleeper are alive although they are not seeing. The soul is a stateof readiness, in bodily organs, to perform their function. It can thus bedescribed as a second potentiality, as well as a first actuality.The conception of an ascending order among living species, with thestages defined by the number and complexity of functions capable of beingperformed by the plant or animal, gives Aristotle the conceptual apparatusfor working out a comprehensive classification of species. There is indeedsome evidence that such a classification was a goal of his biological work,but it is not achieved in his surviving writings, where he is concerned aboveall, it appears, with understanding the differences between animals, andespecially with putting the differences into relation with the organicparts.<sup>22</sup> It has been remarked, too, that many of the ingredients of a theoryof evolution of species are foreshadowed in his theory, but he was firmlyagainst such an idea, as we have observed.This is not the place for a lengthy assessment of Aristotle’s achievementin biology, but a few points may be mentioned. He was handicapped by hisbelief, inherited from some earlier physiologists (against the view of Plato),that the heart, rather than the brain, is the seat of the sensitive soul.<sup>23</sup> Thenerves had not yet been identified as such, and the blood was taken to bethe vehicle for the transmission of messages from sense organs to the centreand vice versa. Blood was thought to be, or to contain, food for the tissuesof the body—the circulation of the blood was not, of course, discovered formany centuries after Aristotle. He took respiration to be a way ofmoderating the natural heat of the body of animals with blood in theirsystem, although he had a use for the concept of
pneuma. or breath, whichhas been mentioned in section 5.The
Generation of Animals contains a detailed study of the reproductionof many species. Aristotle did not understand the contribution of thefemale of the species to the reproductive process: in his theory semen is thevehicle that conveys the formal structure of parent to offspring, while thefemale contributes only the material constituents of the embryo, and (insome species) a protective site for its development. But there areremarkable insights in his analysis of the function and structure of semen.It contains both the formal and the efficient cause of the offspring: itcontains in potentiality the specific form and some, at least, of theindividual characteristics that will be passed on from the parent, and itcontains also the ‘instructions’ for the motions needed to embody these inthe embryo. The transmission takes place not by some crude exchange ofmaterials, but in the form of ‘encoded’ messages.An odd feature of his ‘embryology’ is his continuing belief in thespontaneous generation of members of some species. Some creatures
(testacea) originate from sea water; some plants (for example mistletoe)and animals (grubs) from putrefying matter. What is supplied from sourcesother than parents in these cases is
pneuma, which is the material vehicle oflife, and warmth. So much is perhaps not hard to understand: there is moredifficulty in understanding how matter and warmth alone can supply theform, which in the case of sexual generation requires the subtle andcomplex contributions of the semen.<sup>24</sup>
14THE UNITY OF THE COSMOSPlato’s cosmos, as described in the
Timaeus, was itself an organism—a
zôon or animal; Aristotle never talks of the whole cosmos in such terms.He does, however, in various ways and from time to time indicate clearlyenough that he regards the cosmos as being appropriately named: the wordcarries with it the idea of good order.We must consider also in which of two ways the nature of the wholecontains the good or the highest good, whether as something separateand by itself, or as the order
(taxis) of the parts. Probably in bothways, as an army does. For the good is found both in the order and inthe leader, and more in the latter; for he does not depend on theorder but it depends on him. And all things are ordered togethersomehow, but not all alike—fishes and fowls and plants—and theyare not so disposed that nothing has to do with another, but they areconnected. For all are organised together with regard to a single thing.(Aristotle
Metaphysics 12.10, 1075a11–19, tr. Ross, slightly adapted)In the context it would seem that Aristotle draws an analogy between thecommander of an army and the supreme deity in command of the cosmos—perhaps the mover of the sphere of the fixed stars, or perhaps ‘the divine’ ina collective sense, meaning all of the movers of the spheres. The good thatthey achieve is the eternity of the cosmic order. That is to say, they ensuredirectly the eternal continuity of the motions of all the heavenly spheres,and hence the eternal interchange between contraries in the sublunaryworld, and the eternal continuance of all living species.Aristotle repeats one brief sentence many times, in various contexts:‘nature does nothing without purpose’ (
matên, sometimes translated‘randomly’ or ‘in vain’). This is a notoriously puzzling claim: there seems tobe no room in Aristotle’s theory for a single personified ‘Nature’, actingpurposively like a rational being. Each natural thing has its own nature,and some of the effects of the nature of a thing are purposive only in a veryloose sense, if at all. The sentence seems to be a summing up of the mannerof biological processes; it does not carry us far towards an understandingof the order of the cosmos as a whole.There is a striking statement in the
Politics:The viviparous species have sustenance for their offspring insidethemselves for a certain period, the substance called milk. So thatclearly we must suppose that nature also provides for them in asimilar way when grown up, and that plants exist for the sake ofanimals and the other animals for the good of man, the domesticspecies both for his service and for his food, and if not all at all eventsmost of the wild ones for the sake of his food and of his supplies ofother kinds, in order that they may furnish him both with clothingand with other appliances. If therefore nature makes nothing withoutpurpose or in vain, it follows that nature has made all the animals forthe sake of men.(Aristotle
Politics 1.3, 1256b13 ff.)This is a claim that sounds more like Stoicism than Aristotelianism. In thezoological treatises, animals are described in a more autonomous fashion;it is not asserted that the function of any characteristic of oxen, forinstance, is to supply beef or leather. Man is indeed the ‘highest’ of theanimals, because man shares the divine capability of reason. But thefunction of the parts of animals is not, apparently, to provide for man, butto provide for the continued life of their own species.What Aristotle has in mind is that we can observe a ‘rightness’ in theconstituents of the cosmos and their modes of behaviour. It manifests itselfin different ways. In the case of the elements, it consists in their naturalmotions—towards, away from, or around the centre. In the heavenlyspheres, it consists in their positions and in the regularity of their motions.In the case of the sun, it shows itself in the daily and annual cycles of lightand darkness, summer and winter, which have their effects on the mode oflife and generation of biological species. The complement of these featuresof the cosmic spheres is that each species has its ‘niche’ in the world. Thespecies did not in any sense
find their niche, or grow to fill a previousvacancy: it just is (Aristotle thought) an observable fact that the physicalcosmos provides variously characterized environments, and the livingspecies have just those features that enable them to take advantage ofthem.Aristotle thus differs both from Democritus and from Plato. He differsfrom Plato’s
Timaeus, as we have observed, in denying that the cosmos isthe work of a purposive Creator. But he differs even more fromDemocritus, in denying that the world comes about through accident ormaterial ‘necessity’. The cosmos just is as it is. It is like a well disciplinedarmy, commanded by a good and effective General who keeps his troopsup to the mark in performing their various traditional tasks.
NOTES1 See Barnes [1.28]; for more detailed discussion of
Posterior Analytics, seechapter 2, below.2 See section 12 for discussion of the translation of
aitia as ‘cause’.3 On this subject, see especially Owen [1.72, §8].4 This subject is continued in section 8.5 One argument is derived from Plato’s
Timaeus, although it was in fact usedneither by Plato nor by Aristotle, and those who use the argument do not, itseems, think of aether as the element of the heavens. The argument is thatthere are five regular solids, and so there should be a fifth elementcorresponding to the dodecahedron, which was assigned by Plato to theshape of ‘the whole’. This argument is found in the pseudo-Platonic
Epinomis (981b ff.) and apparently in Plato’s sucessor Xenocrates (fr. 53Heinze, from Simplicius).6 See section 13.7 Aristotle acknowledges his debt to these two in
Metaphysics 12.8.8 The third and fourth spheres enable the model to accommodate theretrogradation of planets. But Aristotle is quite vague about the details ofthese motions, being content, apparently, to leave them to themathematicians.9 Later Greek astronomers put Venus and Mercury between the moon and thesun.10 For comparison of Aristotle’s description with astronomical theory, see [1.63] Neugebauer,
History Part II, pp. 675–89, with diagrams in Part III, pp.1357–8.11 At 1074a12–14, Aristotle says that if the extra spheres added by Callippus tothe sun and the moon are removed, the total should be 47. But something hasgone wrong with the text or the calculation. If Aristotle states the conditioncorrectly, the number should be 49.Another interesting puzzle about the numbers may be mentioned at thisstage; it was first raised, so far as I know, by Norwood Russell Hanson [1.87]. It turns on the question whether the axis on which each sphere turnsshould be regarded as an
axle, with a certain thickness in diameter, or as ageometrical line. If it is an axle, and is fixed at its ends in the surface of its outerneighbour, then when its poles coincide with those of the outer neighbour itshould rotate along with that neighbour. Thus we have a problem at thejunction between two planetary sets. To take the example used above, S−2,which has the rotation of the fixed stars, must impart its own rotation to the
axle of J1, and since J1 rotates about its own axle with the motion of the fixedstars, the sphere J1 will be rotating with
twice that rotation, i.e. in 12 hours.The first sphere of Mars will rotate in 6 hours, the first of Venus in 3 hours,and so on.The solution to this is simply to treat the axis of each sphere as a geometricconstruction and its poles as dimensionless points. This is consistent with thephysical nature of the spheres themselves, and abolishes the consequence of adouble rotation. The points of contact do not
rotate, although of course theyare carried around with the surface in which they are located whenever theydo not coincide with the poles of the superior sphere.12 For a clear discussion of the problems about motion in
On the Heavens, seethe introduction to [1.14] Guthrie.13
Iliad 2.204;
Metaphysics 12.10, 1076a5. The problems connected with theunmoved mover or movers of the spheres has of course been very muchdiscussed. Some notable examples: [1.8] Ross, pp. 94–102; [1.14] Guthrie,introduction; [1.85] Merlan.14 See recent discussions in [1.86] Norman, [1.83] DeFilippo, and [1.74]Waterlow.15 See section 4, above.16 See the discussion of this book in [1.62] Furley, chapter 12. Its authenticityhas been, and still is, doubted by some scholars.17 See [1.80] Sorabji, and [1.77] Cooper.18 This is well explained in [1.81] Woodfield.19 The fullest account of
pneuma is found in
De motu animalium. See [1.9]Nussbaum, especially pp. 143–64.20 See especially [1.18] Balme, Introduction to books 7–10, p.17; [1.90]Pellegrin, and [1.64] Lloyd ch.1 and ch.12.21 See also chapter 3, below.22 See [1.64] Lloyd, ch.1 and ch.12.23 See below, chapter 10, for Galen’s refutation of Aristotle’s view.24 There is a considerable recent literature on Aristotle’s theory of spontaneousgeneration. See, for example, [1.89] Balme, and [1.90] Lennox.
BIBLIOGRAPHYITEMS RELEVANT TO CHAPTERS 1–41.1 The edition of the Greek text of Aristotle, to which reference is standardlymade by page, column and line numbers:
Aristotelis Opera, ed. I.Bekker, 5vols (Berlin, 1831–70).1.2
Index Aristotelicus [Greek word index], ed. H.Bonitz (Berlin, 1870).
Complete English translation1.3
Aristotle: The Revised Oxford Translation, ed. Jonathan Barnes (Bollingenseries), (Princeton, NJ, Princeton University Press, 1984).
Greek texts with English commentary—some notableeditions1.4
Prior and Posterior Analytics, ed. W.D.Ross (Oxford, Clarendon Press,1949).1.5
Physics, ed. W.D.Ross (Oxford, Clarendon Press, 1936).1.6
Aristotle on Coming-to-be and Passing-away (De generatione etcorruptione), ed. H.Joachim (Oxford, Clarendon Press, 1922).1.7
De anima, ed. R.D.Hicks (Cambridge, Cambridge University Press, 1907).1.8
Metaphysics, ed. W.D.Ross (Oxford, Clarendon Press, 1924).1.9
De motu animalium, ed. M.Nussbaum (Princeton, NJ, Princeton UniversityPress, 1978).
Greek texts with English translation (Leob ClassicalLibrary, Harvard University Press)1.10
The Categories, On Interpretation ed. H.P.Cooke;
Prior Analytics, ed.H.Tredennick (1938).1.11
Posterior Analytics, ed. H.Tredennick;
Topics, ed. E.S.Forster (1938).1.12
On Sophistical Refutations, On Coming-to-be and Passing-away, ed. E.S.Forster;
On the Cosmos, ed. D.J.Furley (1955).1.13
Physics, ed. P.H.Wickstead and F.M.Cornford (1929–34).1.14
On the Heavens, ed. W.K.C.Guthrie (1953).1.15
Meteorologica, ed. H.D.P.Lee (1952).1.16
On the Soul and
Parva naturalia, ed. W.S.Hett (1936).1.17
Generation of Animals, ed. A.L.Peck (1943).1.18
Historia animalium books 1–4 and 5–8, ed. A.L.Peck (1965 and 1970); books7–10, ed. D.M.Balme (1991).1.19
Parts of Animals, ed. A.L.Peck, with
Movement of Animals, ed. E.S.Forster(1937).1.20
Minor Works, ed. W.H.Hett (1936).1.21
Problems, ed. W.H.Hett (1926).1.22
Metaphysics, ed. H.Tredennick, with
Oeconomica and
Magna Moralia, ed.G.C.Armstrong (1993).1.23
Nicomachean Ethics, ed. H.Rackham (1926).1.24
Athenian Constitution, Eudemian Ethics, and
Virtues and Vices, ed. H.Rackham (1935).1.25
Politics, ed. H.Rackham (1932).1.26
Rhetoric, ed. J.H.Freese (1926).
English translations of separate works, with commentary,in the Clarendon Aristotle series (Oxford University Press)1.27
Categories and
De interpretatione, by J.L.Ackrill (1963).1.28
Posterior Analytics, by Jonathan Barnes (1975).1.29
Topics, books 1 and 8, by R.Smith (1994).1.30
Physics, books I and II, by W.Charlton (1970); books III and IV, by EdwardHussey (1983).1.31
De generatione et corruptione, by C.J.F.Williams (1982).1.32
De anima, books II and III, by D.W.Hamlyn (1968).1.33
De partibus animalium I and
De generatione animalium I, by D.M.Balme(1972).1.34
Metaphysics, books Gamma, Delta, and Epsilon, by C.Kirwan (1971); booksZeta and Eta, by D.Bostock; books M and N, by J.Annas (1976).1.35
Eudemian Ethics, books 1, 2, and 8, by M.Woods.1.36
Politics 1 and 2, by T.J.Saunders (1995); 3 and 4, by R.Robinson (1962); 5and 6, by D.Keyt (1999); 7 and 8, by R.Kraut (1997).
BibliographiesRecent bibliographies in [1.39]
The Cambridge Companion to Aristotle (1995);also Barnes, Schofield and Sorabji [1.53].
General Introductions to Aristotle1.37 Ackrill, J.L.,
Aristotle the Philosopher (Oxford, Oxford University Press,1981).1.38 Barnes, J.,
Aristotle (Oxford, Oxford University Press, 1982).1.39 Barnes, J., ed.,
The Cambridge Companion to Aristotle (Cambridge,Cambridge University Press, 1995) (contains an extensive bibliography).1.40 W.K.C.Guthrie,
A History of Greek Philosophy, vol. VI:
Aristotle: AnEncounter (Cambridge, Cambridge University Press, 1981).1.41 W.D.Ross,
Aristotle (London, Methuen, 1923).
Proceedings of the Symposium Aristotelicum1.41a
Aristotle and Plato in the Mid-Fourth Century, ed. I.During and G.E.L.Owen, Göteborg, 1960).1.42
Aristote et les problèmes de méthode, ed. S.Mansion (Louvain, PublicationsUniversitaires, 1961).1.43
Aristotle on Dialectic: The Topics, ed. G.E.L.Owen (Oxford, OxfordUniversity Press, 1968).1.44
Naturphilosophie bei Aristoteles und Theophrast, ed. I.Düring (Heidelberg,Lothar Stiehm, 1969).1.45
Untersuchungen zur Eudemischen Ethik, ed. P.Moraux and D.Harlfinger(Berlin, De Gruyter, 1971).1.46
Aristotle on the Mind and the Senses, ed. G.E.R.Lloyd and G.E.L.Owen(Cambridge, Cambridge University Press, 1978).1.47
Etudes sur la, Métaphysique d’Aristote, ed. P.Aubenque (Paris, 1979).1.48
Aristotle on Science: the ‘Posterior Analytics’, ed. E.Berti (Padua, Antenore,1981).1.49
Zweifelhaftes im Corpus Aristotelicum: Studien in einigen Dubia, ed. PaulMoraux and Jurgen Wiesner (Berlin and New York: De Gruyter, 1983).1.50
Mathematics and Metaphysics in Aristotle, ed. Andreas Graeser (Bern/Stuttgart, Paul Haupt, 1987).1.51
Aristoteles’ ‘Politik’, ed. Günther Patzig (Göttingen: Vandenhoecht andRuprecht, 1990).1.52
Aristotle’s Rhetoric, ed. D.J.Furley and A.Nehamas (Princeton, NJ, PrincetonUniversity Press, 1994).
Other collections of essays by various authors1.53 Barnes, Jonathan, Schofield, Malcolm, and Sorabji, Richard (eds),
Articles onAristotle: vol. 1 Science; vol. 2 Ethics and Politics; vol. 3 Metaphysics; vol. 4Psychology and Aesthetics (London, Duckworth, 1975).1.54 Seeck, Gustav Adolf (ed.),
Die Naturphilosophie des Aristoteles (Darmstadt,Wissenschaftliche Buchgesellschaft, 1975).1.55 Gotthelf, Allan (ed.),
Aristotle on Nature and Living Things: Philosophicaland Historical Studies (Bristol Classical Press, and Mathesis Publications,Pittsburgh, 1985.1.56 Gotthelf, Allan, and Lennox, James G. (eds),
Philosophical Issues in Aristotle’sBiology (Cambridge, Cambridge University Press, 1987).1.57 Matthen, Mohan (ed.),
Aristotle Today: Essays on Aristotle’s Ideal of Science(Edmonton, Alberta, Academic Printing and Publishing, 1987).1.58 Devereux, Daniel, and Pellegrin, Pierre (eds),
Biologie, Logique etMétaphysique chez Aristote (Paris, CNRS, 1990).1.59 Judson, Lindsay (ed.),
Aristotle’s Physics: A Collection of Essays (Oxford,Clarendon Press, 1991).
BIBLIOGRAPHY FOR CHAPTER 1General works on Greek science and philosophy of nature1.60 Sambursky, S.,
The Physical World of the Greeks (London, Routledge andKegan Paul, 1956).1.61 Dicks, D.R.,
Early Greek Astronomy to Aristotle (London, Thames andHudson, 1970).1.62 Furley, David,
Cosmic Problems (Cambridge, Cambridge University Press,1989).1.63 Neugebauer, O.,
A History of Ancient Mathematical Astronomy (Berlin/Heidelberg/NY, Springer Verlag 1975).1.64 Lloyd, G.E.R.,
Methods and Problems in Greek Science: Selected Papers(Cambridge University Press, 1991).1.65 Sorabji, Richard,
Time, Creation, and the Continuum: Theories in Antiquityand the Early Middle Ages (London, Duckworth, 1983).1.66 ——
Matter, Space, and Motion: Theories in Antiquity and their Sequel(London, Duckworth, 1988).
General studies on Aristotle’s philosophy of nature1.67
Aristotle Today: Essays on Aristotle’s ideal of science, ed. Mohan Matthen(Edmonton, Academic Printing and Publishing, 1989).1.68 Barnes, Schofield and Sorabji [1.53], vol 1, Science.1.69 Barnes [1.39]
The Cambridge Companion to Aristotle. [With goodbibliography.]1.70 Graham, Daniel W.,
Aristotle’s Two Systems (Oxford, Oxford UniversityPress, 1987).1.71 Mansion, Augustin,
Introduction à la physique aristotélicienne, 2nd edn(Louvain, 1946).1.72 Owen, G.E.L.,
Collected Papers in Greek Philosophy, ed. Martha Nussbaum(Ithaca, NY, Cornell University Press, 1986). Especially no. 8 ‘Aristotle:method, physics and cosmology’ and no. 10
‘Tithenai ta phainomena’.1.73 Solmsen, Friedrich,
Aristotle’s System of the Physical World (Ithaca, NY,Cornell University Press, 1960).1.74 Waterlow, S.,
Nature, Change, and Agency in Aristotle’s Physics (Oxford,Clarendon Press, 1982).
Causation1.75 Annas, J., ‘Aristotle on inefficient causes’,
Philosophical Quarterly 32(1982), 319.1.76 Balme, D.M., ‘Teleology and necessity’, in Gotthelf and Lennox, [1.56], 275–86.1.77 Cooper, John M., ‘Hypothetical necessity and natural teleology’, in Gotthelfand Lennox [1.56], 243–74.1.78 Gotthelf, Allan, ‘Aristotle’s conception of final causality’, in Gotthelf andLennox [1.56], 204–42.1.79 Lennox, James, ‘Teleology, chance, and Aristotle’s theory of spontaneousgeneration’,
Journal of the History of Philosophy, 20 (1982), 219–38.1.80 Sorabji, Richard,
Necessity, Cause and Blame: Perspectives on Aristotle’sTheory (London, Duckworth; Ithaca, NY, Cornell University Press, 1980).1.81 Woodfield, Andrew,
Teleology (Cambridge, Cambridge University Press,1976).
Motion and theology1.82 Bogen, James, and McGuire, J.E., ‘Aristotle’s great clock: necessity,possibility and the motion of the cosmos in
De caelo 1.12’,
PhilosophyResearch Archives 12 (1986–87), 387–448.1.83 DeFilippo, Joseph, ‘Aristotle’s identification of the prime mover as god’,
Classical Quarterly 44 (1994), 393–409.1.84 Kahn, C., ‘The place of the prime mover in Aristotle’s teleology’, in Gotthelf[1.55].1.85 Merlan, P., ‘Aristotle’s unmoved movers’,
Traditio 4 (1946), 1–30.1.86 Norman, Richard, ‘Aristotle’s Philosopher-God’,
Phronesis 14 (1969), 63.Repr. in Barnes, Schofield and Sorabji [1.53], vol. 4, 183–205.1.87 Hanson, N.R., ‘On counting Aristotle’s spheres’,
Scientia 98 (1963), 223–32.
Matter and elements1.88 Moraux, Paul, ‘Quinta essentia’, in Pauly-Wissowa,
Realencyclopädie 24,1171–226.
Biology1.89 Balme, D.M., ‘Development of biology in Aristotle and Theophrastus: theoryof spontaneous generation’,
Phronesis 7 (1962), 91–104.1.90 Lennox, James ‘Teleology, chance, and Aristotle’s theory of spontaneousgeneration’,
Journal of Hellenistic Studies 20 (1982), 219–38.1.91 Pellegrin, Pierre,
La Classification des animaux chez Aristote: Statut de labiologie et unite de l’Aristotélisme (Paris, Les Belles Lettres, 1982).