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The Ontology of Causality in Aristotle
by Bryan Register

Date: 1 May 99
Forum: University of Texas at Austin
Copyright: Bryan Register

Note: The author may or may not still agree with the views expressed in this paper.

This paper will investigate four tightly related concepts in Aristotelian science: 'nature', 'form', 'potential', and 'actuality'. I will be guided somewhat by Hankinson's treatment "Philosophy of Science", but more deeply by section IV of Allan Gotthelf's paper "Aristotle on Final Causality".

Gotthelf calls our attention to the notion of 'nature' by noting that:

All these things which exist by nature - simple bodies, inanimate compounds,

plants, animals and their parts - move and/or change in ways characteristic of themselves if not impeded, which is to say, each has a nature . If an entity or material body is acting in such a characteristic way, it is a sufficient explanation of its action to identify that it is acting in accordance with its nature. (Gotthelf, 232-233)

Gotthelf suggests that 'explanation' and 'nature' are closely related concepts. A brief look at 'explanation' may help us better understand 'nature', and will also help show the connections between ontological and epistemic concerns in Aristotle.

In Posterior Analytics (APo), Aristotle presents his theory of the demonstration, or explanatory syllogism. Demonstration is a special kind of syllogism which not only proves the truth of its conclusion, but also explains why the conclusion holds. Aristotle writes that

There are three things involved in demonstrations: one, what is being demonstrated, or the conclusion (this is what holds of some kind in itself); one [sic?], the axioms (axioms are the items from which demonstrations proceed); third, the underlying kind whose attributes - i.e. the attributes incidental to it in itself - the demonstration makes plain. (APo I.7. 74a39-74b2)

Aristotle is referring in this summary to the parts of an explanatory syllogism. The conclusion, of course, is the proposition which is proved and the truth of which is explained by the demonstration. The axiom is apparently the first premise of the demonstration. However, the third feature to which Aristotle refers is 'the underlying kind whose attributes the demonstration makes plain'. Clearly a kind, or rather the term for the kind, is not a premise. Since Aristotle seems to have said that the three parts of a demonstration are a premise, a conclusion, and a term, his account seems wrong. Thus the passage requires a closer look.

The 'conclusion' is parenthetically described as 'what holds of some kind in itself'. Now, what holds of something is not a premise, but a predicate. So Aristotle seems to mean, by 'conclusion', not the proposition demonstrated, but rather the predicate term of the proposition demonstrated (which is of course also the conclusion in the ordinary sense).

The 'third element' was a kind term and it was a kind term 'whose attributes the demomonstration makes plain'. The demonstration will make plain, we can expect, why some predicate term (the 'conclusion') holds of some subject term, or why the referent of the subject term has a certain attribute for which the predicate is the term. Thus we can read the third element as meaning the subject term of the conclusion, or as the term of which the 'conclusion' (in its unusual sense as the predicate of the conclusion) holds.

The 'axioms', however, are not accounted for. While before focusing on the parenthetical explanations, we seemed to have two propositions and one term comprising the demonstration, we now seem to have two terms and one proposition. However, the 'axioms' are plural. Thus there are at least two of them. Since the 'conclusion' (as predicate) and third element were the predicate and subject, respectively, of the conclusion of the demonstration, we need two premises. Since the demonstration consists of three elements, two of which are within the conclusion and one of which must have at least two members, we may take it that these two members - the 'axioms' - are the premises of the demonstration.

Aristotle also provides an example demonstration, saying:

The bright side's being toward the sun, A ; getting light from the sun, B ; the

moon, C . B, getting light from the sun, holds of C, the moon; and A, the bright side's bring toward that from which it gets light of B : hence A holds of C through B . (APo I.34. 89b17-20)

Arrayed as a syllogism, this reads:




The predicate term A, 'the bright side's being toward the sun', holds of the middle term B, 'getting light from the sun'; that is, that which gets its light from the sun has its bright side toward the sun. The middle term B holds of the subject term C, the moon; that is, the moon is a thing that gets its light from the sun. Thus we have demonstrated that the predicate term A holds of the subject term C (the moon has its bright side toward the sun) because of B's holding of C and A's holding of B. (Actually, it seems that this demonstration is backwards; the fact that the moon faces the sun seems to explain why it is lit by the sun rather better than the fact that the moon is lit by the sun explains the physical location of the moon. But as we are focused only on the structure of demonstration, we can ignore this matter.)

The connection between 'nature' and 'explanation' is that the B term, the explanatory term, specifies the nature (or some feature of the nature) of the C term in virtue of which the A term can be predicated over it; in virtue of which A holds of C. Thus the relation seems to be a causal one; it is C's B-ness which causes C's A-ness.

Now let us turn elsewhere in Aristotle to get a better grip on the notion of a 'nature'. Physics (Phys) II.1. carries an extensive discussion of 'nature'. Aristotle opens the chapter by noting what things have a nature: "Of the things that exist, some exist by nature, some from other causes. By nature the animals and their parts exist, and the plants and the simple bodies (earth, fire, air, water) - for we say that these and the like exist by nature." (Phys. II.1. 192b9-11) Note that a thing's nature is referred to as a cause of the existence of the thing.

Aristotle continues to explain just what a nature is: "...each of them [things which have natures] has within itself a principle of motion and stationariness (in respect of place, or of growth and decrease, or by way of alteration)." (Phys. II.1.192b14-16) Having such a principle is taken by Aristotle to be that which differentiates those things with natures from those without. Since Aristotle has referred to something's nature both as the cause of the existence of the thing, and as the principle of its motion, we may take it that something's nature is a causal feature of the thing. We may expect to find that something's nature just is the cause of its motions and at least certain of its other features.

Some things do not have a nature. These are artifacts. The distinction is apparently that that which exists in the natural world exists by nature, while that which is human-made does not. Aristotle says that "...a bed and a coat and anything else of that sort, qua receiving these designations - i.e. in so far as they are products of art - have no innate impulse to change." But he continues to note that "...insofar as they happen to be composed of stone or of earth or of a mixture of the two, they do have such an impulse, and just to that extent.." (Phys. II.1. 192b16-21) Thus, even artifacts have a nature in a kind of degenerate sense. The imposed structure of human design does not provide artifacts with a nature, but it also does not remove the nature of the elements which compose the artifact. Artifacts won't do anything in virtue of the structure imposed on them by art, but they will continue to do whatever they were always doing according to the nature of their substratum.

We should explore the relationship between the notions of 'nature' and 'form'. First I will investigate just what 'form' is on its own. Aristotle says that "The 'form'... means the 'such', and is not a 'this' - a definite thing; but the artist makes, or the father generates, a 'such' out of a 'this'; and when it has been generated, it is a 'this such'." (Meta VII.8. 1033b22-24) The first sentence is slightly polemical and is directed at Plato. For Plato, that in virtue of which something is what it is is external to the thing and is reified into an independently existing Form. Aristotle is noting that the things he will call forms do not have an independent existence; a form is not 'a definite thing'. The vocabulary of 'such' and 'this' is directed at classification and individuality. This vocabulary (when translated) works rather nicely with our ordinary language. In an ordinary sentence like "I like to read books, such as this one", the word 'this' functions as an indexical, selecting some particular ordinary object, while the word 'such' connects that particular to the general class which it is being called a member of. Thus 'form' is somehow connected with classification of what a thing is, as distinct from the individuality of the thing.

Aristotle moves on to say that "...when we have a whole, such and such a form in this flesh and in these bones, this is Callias or Socrates; and they are different in virtue of their matter (for that is different), but the same in form; for their form is indivisible." (Meta VII.8. 1034a5-8) Aristotle is here claiming that form is held in common by things which are members of the same class, while it is their matter in virtue of which they are distinct things. Form integrates the world, while matter differentiates it.

Aristotle also provides some examples: "...what is still weather? Absence of motion in a large extent of air; air is the matter, and absence of motion is the actuality and substance. What is a calm? Smoothness of sea; the material substratum is the sea, and the actuality or form is smoothness." (Meta VIII.2. 1043a23-25) Note that the word 'actuality' is identified with both 'form' and 'substance'. In these examples, form seems to be the shape or structure of matter. Absence of motion is a large-scale structural feature of bodies of air or water. Another passage will make this clearer: "...the actuality or the formula is different when the matter is different; for in some cases it is the juxtaposition, in others the mixing, and in others some other of the attributes we have named." (Meta VIII.2. 1043a12-14) Here, form (remember that 'actuality' was identified with form in the last passage) is identified with the 'juxtaposition', 'mixing', or 'other attributes' of the matter. This strongly suggests that form is arrangement of matter.

Recall, however, that form is also involved in the categorization of things. If form is both (in some sense) the category into which something fits, and also the arrangement of the thing's matter, then form is an arrangement of matter which is common to different things.

We can get a little bit clearer on the nature of form by glancing at the De Anima (DA). Here Aristotle pronounces his theory that the soul is the form of the living organism: "...the soul must be a substance in the sense of the form of a natural body having life potentially within it." (DA II.1. 412a20-21) Aristotle says here that the natural body which is informed by the soul has life potentially within it. Since, if the soul is the form of the organism, then the body of the organism must be its matter, Aristotle is saying that the matter potentially has life within it. But Aristotle routinely describes matter as being potentially what it will actually be when it is informed. So if life is the thing which this matter has as a potentiality, and soul is the eventual form of the thing, then soul and life are identical.

It will thus be interesting to see what Aristotle says that life is. He says that

...this word [life] has more than one sense, and provided any one alone of these is found in a thing we say that thing is living - viz. thinking or perception or local movement and rest, or movement in the sense of nutrition, decay and growth. Hence we think of plants also as living, for they are observed to possess in themselves an originative power through which they increase or decrease in all spatial directions... (DA II.2. 413a23-27)

Life, then, is characterized in terms of certain performances: thought, sensing, moving. Now, if life is soul, and soul is form, then at least certain forms are characterized not only in terms of physical structure of that which they inform but also in terms of typical activities of that which they inform.

Now that we are clear(er) on the notion of 'form' we can try to understand the relation between 'form' and 'nature'. I will begin here by building the case that 'nature' and 'form' mean the same thing. One section of Aristotle's philosophical lexicon, Metaphysics (Meta) V, is devoted to 'nature'. Here he writes that regards the things that are or come to be by nature, though that from which they naturally come to be or are is already present, we say they have not their nature yet, unless they have their form or shape. That which comprises both of these exists by nature, e.g. the animals and their parts; and nature is both the first matter..., and the form or substance, which is the end of the process of becoming. (Meta V.4. 1015a4-11)

Since Aristotle says that the elements have natures according to which they act, we can take the reference to 'first matter' to indicate matter inasmuch as it is the kind of matter that it is (has the form of its kind of matter as opposed to pure formless matter) and which thus seeks the natural place of its kind of matter. Now, since nature is identified with matter inasmuch as it is informed, and he goes on to say that nature is also form, it seems that Aristotle is identifying form and nature.

Aristotle also said that form is the 'end of the process of becoming', suggesting that form is a goal of some kind. But it is worth noting that he has said this for non-biological entities as well as biological entities. Unless he will be attempting to apply teleological explanations to non-biological entities, Aristotle must mean something rather odd by 'end' here. We will look to this point again later.

The thesis that nature is form appears to be confirmed by the next two sentences:

And from this sense of 'nature' every substance in general is in fact, by an extension of meaning, called a 'nature', because the nature of a thing is one kind of existence. From what has been said, then, it is plain that nature in the strict sense is the substance of things which have in themselves, as such, a source of movement; for the matter is called the nature because it is qualified to receive this... (Meta V.4. 1015a11-14)

There are two reasons why this suggests that nature is form. First, 'matter is called the nature because it is qualified to receive this', indicating that matter's being called a nature is an extended sense of the term. Second, Aristotle says that 'nature in the strict sense is the substance of things which have in themselves... a source of movement....' Now, this simply repeats the characterization of 'nature'. However, since nature is the substance of these things, and the substance of something is primarily its form as Aristotle argues in Meta VII, this strongly suggests that nature is just form.

But we can see that nature is not quite just form. Aristotle provides several examples of artifacts to which he ascribes form. For instance: "...that there is a bronze sphere, this we make. For we make it out of bronze and the sphere; we bring the form into this particular matter, and the result is a bronze sphere." (Meta VII.8. 1033b8-10) So a bronze sphere which is made has a form, but since it is an artifact, it does not have a nature. This suggests that 'nature' is synonymous with 'form' as applied to living things and natural objects.

Before we proceed with this conclusion, one rather recalcitrant passage should be dealt with. When Aristotle introduces his claim that the soul is the form of the living body, he tries to clarify this account by comparing the organism to an axe:

Suppose that a tool, e.g. an axe, were a natural body, then being an axe would have been its essence, and so its soul; if this disappeared from it, it would have ceased to be an axe, except in name. As it is, it is an axe; for it is not of a body of that sort that what it is to be, i.e. its account, is a soul, but of a natural body of a particular kind, viz. one having in itself the power of setting itself in movement and arresting itself. (DA II.1. 412b12-17)

This is a very complicated passage. First, we are asked to pretend for a moment that an axe is natural. Only were the axe natural - possessed of a nature - would it have an essence, perhaps 'axeness'. This would also make it so that the axe had a soul. But real, non-natural axes still have within themselves a principle of motion.

The passage is doubly confusing. First, Aristotle seems to identify nature with 'essence' and thus to deny having an 'essence' to an axe because it is an artifact. But elsewhere he writes that "...each primary and self-subsistent thing is one and the same as its essence." (Meta VII.6. 1032a4-5) Now surely the axe has not become an accident just by being an artifact. Aristotle seems to be contradicting himself here. If a bronze sphere can be a substance (combination of form and matter) despite being an artifact, then a bronze sphere can have an essence because having an essence is identical with being a substance. Thus an axe's being an artifact should not prevent it from having an essence despite the fact that it does prevent it from having a nature.

Aristotle was probably being incautious in the DA passage. The Meta passages come at moments when he is focused on clarifying the meaning of 'essence', 'form' and 'substance', while in the DA passage Aristotle is focused on the notion of 'soul'. We should therefore disregard the misleading comment in DA and accept that artifacts, despite lacking natures, do possess essences.

The second confusing element is Aristotle's claim that artifactual axes have a principle of motion, despite the fact that a nature has been repeatedly characterized as a principle of motion and artifacts repeatedly characterized as not having natures. Again, he seems to have contradicted himself. Two alternative solutions present themselves. On the one hand, assuming that I have correctly read the passage, then Aristotle may be referring to the principle of nature not of the axe as such, but of the materials out of which the axe is made. In this case, he is writing somewhat clumsily. On the other hand, I may have misread the passage, misplacing the hypothetical modification. The passage is difficult to read and it is not perfectly clear whether the second sentence is intended to be hypothetical or not. If this sentence is hypothetical, then Aristotle is saying that were an axe natural, it would possess a principle of motion, which is exactly what we would expect him to say. Supporting this suggestion is the fact that, while Aristotle introduces the passage as a thought experiment, if this second sentence is not a part of that thought experiment then there actually is no thought experiment at all; the rest of the passage explicitly considers what is the case since the thought experiment is counterfactual. But on either suggestion, Aristotle is not contradicting himself, he is merely being somewhat unclear in his writing.

So we are now clear on the relationship between the notions of 'nature' and 'form'. A 'nature' is the principle of motion of a non-artifactual entity, while 'form' is common structure and sometimes common function of any entity. Actually, we are now in a position to understand a hierarchy of types of structure. Forms inform all substances. Natures are the forms of natural substances; organisms and natural matter. Souls are the natures of organisms. Thus all souls are natures and all natures are forms.

Now we can move very briefly to the notion of 'potential' (or 'capacity' as it is translated in my edition of Aristotle). Gotthelf points out that " addition to having a nature, each natural thing has potentials - potentials to change certain other things in certain ways... and potentials to be changed by certain other things in certain ways..." (Gotthelf, 233) A reading of Meta V.12 will confirm Gotthelf's account. Here Aristotle says that "Capacity is the source, in general, of change or movement in another thing or in the same thing qua other, and also the source of a thing's being moved by another thing or by itself qua other." (Meta V.12. 1019a18-20) Aristotle is saying that what are called something's capacities are its abilities to affect other things or to be affected by other things. This should be distinguished from a thing's nature because its nature is its internal ability to generate movement, while a capacity is a relational feature; an external ability to generate movement or allow movement to be generated in oneself.

I call attention to potentials primarily because Gotthelf employs them in his summary:

Every process in nature, every motion or change, according to Aristotle, is action in accordance with a nature or the actualization of a coordinate pair of active and passive potentials or the sum of some combination of these. A natural motion or change is explained when it is shown to be the result of: action in accordance with one or more natures and/or actualizations of one or more irreducible potential-pairs. (Gotthelf, 234)

This summary brings together most of what we have discussed so far. Nature is an internal capacity to generate action, and something's actions are explained when our attention is called to those features of something's nature which are the internal capacity to generate the action to be explained. The example of the eclipse which I cited above is an example of explanation by potential, rather than nature. It is the moon's potential to be affected by the sun in a certain way which explains its characteristic reflective behavior (or at least that is what Aristotle would have said had he gotten the explanation in the right order).

Gotthelf also calls our attention to the fourth and last concept we should explore, which is the notion of 'actuality' or 'actualization'. Already we have seen 'actuality' simply identified with form, while 'potential' has been identified with matter. Aristotle notes that "...that for the sake of which a thing is, is its principle, and the becoming is for the sake of the end; and the actuality is the end, and it is for the sake of this that the potentiality is acquired." (Meta IX.8. 1050a7-10) Aristotle is beginning to suggest an extremely interesting account of what it is to be what something is. Actuality has been identified with form, but here actuality is identified with the end toward which something tends. Thus form, what something is, is also end, what something strives toward. Again we should note that, unless Aristotle intends to suggest a teleological account of the behaviors of non-biological entities, his sense of 'end' is rather strange.

Also, Aristotle seems to be pointing here to his account in the Generation of Animals (GA) when he says that ' is for the sake of the end that the potentiality is acquired.' In his account of the generation of animals, Aristotle claims that the menstrual fluid, which is the matter relative to human beings, takes on human form when it is exposed to semen, which carries the form. The form is transferred into the menses by some kind of physical interaction with the semen. Aristotle writes that "...the male's nature, in those that emit seed, uses the seed as a tool containing movement in actuality, just as in the productions of an art the tools are in movement; for the movements of the art are in a way in them." (GA I.22. 730b19-24) This account should inform our understanding of actuality, and thus nature and form. Here, the form is transmitted by a kind of fluid dynamic. The semen has some kind of internal motion which is transmitted into the menses and generates an identical (or nearly so) motion within the menses. Once moved in this way, the menses, which had been a potential organism, becomes an actual organism. Thus the transference of form is the transference of certain characteristic motions. But if this is right, then form or nature just is a kind of motion (in addition to structural features). We should expect Aristotle to say that, since form is a kind of motion, a thing expresses its nature (form) over time, through its motions. And indeed he does say this: "For the action is the end, and the actuality is the action. Therefore even the word 'actuality' is derived from 'action', and points to the fulfillment." (Meta IX.8. 1050a21-23) What is actual is form, and moreover, what is actualized through time is form. Indeed, were a thing not to act in accordance with its form, it would not be actualizing its form; it would remain matter.

One final passage should help verify that this is Aristotle's treatment of the relation between form and actualization. In De Caelo (DC) Aristotle writes that "...the movement of each body to its own place is motion towards its own form." (DC IV.3. 309a33-34) Each kind of body has its natural place. This location, Aristotle is indicating, is as much a feature of the form of the thing as the physical structure, and so 'the movement of each body to its own place' is merely the actualization of form. (This may be why the Prime Mover, who is completely actual and not at all potential, has nowhere to go and simply spins in a circle all the time; its form is perfectly expressed already and thus it cannot express it over time.)

I have twice noted that, unless Aristotle means something rather odd by 'end', he seems to be committing himself to a teleological account of non-organismic motions. I think that we can now see that Aristotle might just mean something rather odd by 'end'. Consider the account of the generation of animals and the meaning of 'life'. The transfer of form into the menses through contact with the semen is a transference of motions, which motions just are the form (or at least are the expression of the form through time). The organism's growth, physical structure, and functions are all expressions of the form as well. But so is the motion towards their natural places of natural but non-living entities. In neither case is reference to a goal necessary to make sense of the account. A thing's behavior requires explanation by reference to the end of the thing only because Aristotle employs the word 'end' as a synonym for form, and behavior must be explained in reference to form. Aristotle simply does not mean 'goal' when he says 'end'. (Of course, this hardly means that no explanation in Aristotle is teleological. It only means that not all of them must be.)

In Aristotle's account, then, form and action are internally related. Something's form just is its structure and its actions, and its actions are exclusively the expression of its form through time, just as its structure is the expression of its form in space. We cannot even speak of form as distinct from actions or actions as distinct from form.

Works Cited or Consulted

Aristotle. The Complete Works of Arisotle. ed. Barnes, Jonathan. Princeton UP: Princeton, 1984.

Aristotle. Parts of Animals and Generation of Animals. trans., ed., and with comments by Balme, David. Oxford UP: Oxford, 1992.

Aristotle. Posterior Analytics. trans., ed., and with comments by Barnes, Jonathan. Oxford UP: Oxford, 1993.

Barnes, Jonathan, ed. The Cambridge Companion to Aristotle. Cambridge UP: Cambridge, 1995.

Barnes, Jonathan. "Metaphysics". in Barnes, 1995.

Gotthelf, Allan. "Aristotle on Final Causality". Review of Metaphysics 30, 1976. pgs. 226-254.

Hankinson, R. J. "Philosophy of Science". in Barnes, 1995.

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