Book 1 chapter 1 of Parts of Animals provides an overview of Aristotle’s perspective on explanation in general. It is a nice synthetic text that brings together many of Aristotle’s core concerns, and shows his vision of how natural science ought to fit in with broader philosophy.
He begins by distinguishing between mere acquaintance with an area of study and being educated in it. “For an educated [person] should be able to form a fair judgment as to the goodness or badness of an exposition” (Complete Works, Barnes ed., vol. 1, p. 994). This seems to apply to any subject whatsoever.
Next he raises the more specific question of method. “It is plain then that, in the science which inquires into nature, there must be certain canons, by reference to which a hearer shall be able to criticize the method of a professed exposition, quite independently of the question whether the statements made be true or false” (ibid).
Continuing to emphasize the critical thinking that is the mark of an educated person, he makes it explicit that some of the most important questions about a subject are what I would call second-order questions, having to do with how we ought to approach the matter at hand. The educated person will give due emphasis to these, rather than naively rushing to deliver judgments on questions of fact.
“Ought we, for example (to give an illustration of what I mean) to begin by discussing each separate substance — man, lion, ox, and the like — taking each kind in hand independently of the rest, or ought we rather to lay down the attributes which they have in common in virtue of some common element of their nature? For genera that are quite distinct present many identical phenomena, sleep, for instance, respiration, growth, decay, death, and other similar affections and conditions…. Now it is plain that if we deal with each species independently of the rest, we shall frequently be obliged to repeat ourselves over and over again; for horse and dog and man present every one of the phenomena just enumerated” (ibid).
The educated person looks for explanations, not just facts or correspondences. The specific “dogginess” of a dog, for example, does not explain its sleeping, breathing, and so on. Instead these activities, which it shares with many other animals, are explained by natures common to all of them.
Further, the kind of method Aristotle commends to us is not a matter of following recipes by rote. Instead, it is a thinking approach that involves persistently following the thread of explanations wherever it leads.
“So also there is a like uncertainty as to another point now to be mentioned. Ought the student of nature follow the plan adopted by the mathematicians in their astronomical demonstrations, and after considering the phenomena presented by animals, and their several parts, proceed subsequently to treat of the causes and the reason why; or ought he to follow some other method? Furthermore, the causes concerned in natural generation are, as we see, more than one. There is the cause for the sake of which, and the cause whence the beginning of motion comes. Now we must decide which of these two causes comes first, which second. Plainly, however, that cause is the first which we call that for the sake of which. For this is the account of the thing, and the account forms the starting-point, alike in the works of art and in works of nature. For the doctor and the builder define health or house, either by the intellect or by perception, and then proceed to give the accounts and the causes of each of the things they do and of why they should do it thus” (p. 995).
He raises the question of which kind of cause comes first, because he wants to suggest a different answer from that of the pre-Socratic “physicists” who attempted to explain everything by properties of different kinds of matter. Elsewhere he says that Plato and the atomist Democritus (whose writings are lost) did better than others at following the thread of explanation, but he considers the elaborated account of ends or “that for the sake of which” to be one of his own most important contributions.
Notably he only mentions two kinds of cause here, rather than the classic four. Similarly, there are passages in other texts where he lists a different number of categories than the canonical ten from the Categories. Later authors often viewed things like causes and categories in a reified, univocal way, as susceptible to exact enumeration. But for Aristotle, these are abstractions from a concrete reality that comes first, to be wielded in a context-sensitive way, so the canonical enumerations are not absolute.
Aristotle’s understanding of the “beginning of motion” is different from that promoted by early modern physics. Conventionally in the reading of Aristotle, the “beginning of motion” is associated with the efficient cause, and these two terms are understood in a somewhat circular way, which is really informed by some broadly intuitive sense of what a “beginning” of motion is. Early modern writers assumed that this “beginning” must be some kind of immediate impulse or force. Aquinas associated it with God’s act of creation and with the free acts of created beings. For Aristotle himself it is neither of these.
My best reading of efficient cause is that it is the means by which an end is realized. In many cases the end is realized not by just one means but by a hierarchy of means (e.g., art of building, carpenter, carpenter’s hammer, hammer’s blow). Aristotle and the scholastics emphasized the top of such hierarchies (e.g., the art of building for Aristotle; God or some metaphysical principle for the scholastics), whereas the early moderns emphasized the bottom (e.g., the hammer’s blow), akin to the proximate cause of concern to liability lawyers. For Aristotle, the art of building and not the hammer’s blow is the true “beginning” of the motion of house construction, because it provides the guiding thread of explanation for the whole process of building the house. But even the art of building is still just a means that gets its meaning from the reasons why we would want to build a house in the first place.
He continues, “Now in the works of nature the good and that for the sake of which is still more dominant than in works of art, nor is necessity a factor with the same significance in them all; though almost all writers try to refer their accounts to this, failing to distinguish the several ways in which necessity is spoken of. For there is absolute necessity, manifested in eternal phenomena; and there is hypothetical necessity, manifested in everything that is generated as in everything that is produced by art, be it a house or what it may. For if a house or other such final object is to be realized, it is necessary that first this and then that shall be produced and set in motion, and so on in continuous succession, until the end is reached, for the sake of which each prior thing is produced and exists. So also is it with the productions of nature. The mode of necessity, however, and the mode of demonstration are different in natural science from what they are in the theoretical sciences [e.g., mathematics]…. For in the latter the starting-point is that which is; in the former that which is to be. For since health, or a man, is of such and such a character, it is necessary for this or that to exist or be produced; it is not the case that, since this or that exists or has been produced, that of necessity exists or will exist. Nor is it possible to trace back the necessity of demonstrations of this sort to a starting-point, of which you can say that, since this exists, that exists [as one might do in mathematics]” (ibid).
In Aristotle’s usage, “nature” applies to terrestrial things that are observably subject to generation and corruption. He earlier referred to astronomical phenomena like the apparent motions of the stars and planets as “eternal” because on a human scale of time, these are not observably subject to generation and corruption. For Aristotle, absolute necessity could only apply to things that are absolutely unchanging. We may have a different perspective on astronomy, but that does not affect the logical distinction Aristotle is making. His key point here is that things subject to generation are not subject to absolute necessity. Leibniz took this a step further and argued that hypothetical necessity is the only kind there is. Kant, in arguing that hypothetical and disjunctive judgment (“if A then B” and “not both A and B“) are more fundamental than categorical judgment (“A is B“), made a related move.
Hypothetical necessity has a particular form that is worth noting. As Aristotle points out in the quote above, under hypothetical necessity “it is not the case that, since this or that exists or has been produced, that of necessity exists or will exist”. To give a positive example, hypothetical necessity says that to continue living, we must eat. But it does not in any way dictate a particular series of motions that is the only way this can be accomplished, let alone the whole series of eating-related actions throughout one’s life. Neither does it dictate that we will eat in any particular instance.
How we meet a particular need is up to us. The reality of this flexibility built into nature is all we need to explain freedom of action. Humans can also affirmatively embrace commitments and act on them; that too is up to us. Freedom is not an arbitrary or supernatural power; it simply consists in the fact that nature is flexible, and many things are up to us.
Aristotle contrasts the way a thing is naturally generated with the way it is. “The best course appears to be that we follow the method already mentioned — begin with the phenomena presented by each group of animals, and, when this is done, proceed afterwards to state the causes of those phenomena — in the case of generation too. For in house building too, these things come about because the form of the house is such and such, rather than its being the case that the house is such and such because it comes about thus…. Art indeed consists in the account of the product without its matter. So too with chance products; for they are produced in the same way as products of art” (pp. 995-996).
“The fittest mode, then, of treatment is to say, a man has such and such parts, because the essence of man is such and such, and because they are necessarily conditions of his existence, or, if we cannot quite say this then the next thing to it, namely, that it is either quite impossible for a man to exist without them, or, at any rate, that it is good that they should be there. And this follows: because man is such and such the process of his development is necessarily such as it is; and therefore this part is formed first, that next; and after a like fashion should we explain the generation of all other works of nature” (p. 996).
This way of reasoning backwards from an essence to its prerequisites is complemented by the fact that for Aristotle (and Plato) essences themselves are a prime subject of investigation, and not something assumed. “Begin with the phenomena”, he says.
Many 20th century philosophers have objected to presumptuous talk about the “essence of man”, and to any explanation in terms of essence. But these objections presuppose that the essence is something assumed, rather than being an object of investigation as it clearly was for Plato and Aristotle. Here also it is needful to distinguish between what we might call the distinguishing essence of humanity used to pick out humans — e.g., “rational/talking animal” — and what Leibniz later called the complete essence of each individual. Clearly also, the parts of the human body do not follow directly from “rational/talking animal”, but from many other attributes “presented in the phenomena”. It turns out that humans share these attributes with other animals, and they can therefore be conceptualized as attributes of common genera to which we and those other animals belong.
Because essences themselves are a prime subject of investigation and are ultimately inferred from phenomena, the kind of teleological reasoning Aristotle recommends always has a contingent character, which is how it naturally accounts for what the moderns call freedom. This contingency is built into in the “hypothetical” character of hypothetical necessity.
“Does, then, configuration and color constitute the essence of the various animals and their several parts? For if so, what Democritus says will be correct…. And yet a dead body has exactly the same configuration as a living one; but for all that it is not a man. So also no hand of bronze or wood or constituted in any but the appropriate way can possibly be a hand in more than name. For like a physician in a painting, or like a flute in a sculpture, it will be unable to perform its function” (p. 997).
Aristotle was the historic pioneer of “functional” explanation. Here he insists that the essences of living beings and their parts must be understood in terms of their characteristic activities. This development for the sake of biology parallels the deeper development of the meaning of “substance” in the Metaphysics as “what it was to be” a thing, and as actuality and potentiality.
“If now the form of the living being is the soul, or part of the soul, or something that without the soul cannot exist; as would seem to be the case, seeing at any rate that when the soul departs, what is left is no longer an animal, and that none of the parts remain what they were before, excepting in mere configuration, like the animals that in the fable are turned into stone; if, I say, this is so, then it will come within the province of the natural scientist to inform himself concerning the soul, and to treat of it, either in its entirety, or, at any rate, of that part of it which constitutes the essential character of an animal; and it will be his duty to say what a soul or this part of a soul is” (ibid).
Here it is important that we consider soul in the “phenomena first” way that Aristotle develops it.
“What has been said suggests the question, whether it is the whole soul or only some part of it, the consideration of which comes within the province of natural science. Now if it be of the whole soul that this should treat, then there is no place for any philosophy beside it…. But perhaps it is not the whole soul, nor all of its parts collectively, that constitutes the source of motion; but there may be one part, identical with that in plants, which is the source of growth, another, namely the sensory part, which is the source of change of quality, while still another, and this is not the intellectual part, is the source of locomotion. For other animals than man have the power of locomotion, but in none but him is there intellect. Thus it is plain that it is not of the whole soul that we have to treat. For it is not the whole soul that constitutes the animal nature, but only some part or parts of it” (p. 998).
Aristotle’s opposition to treating the soul as a single lump reflects his overall functional, activity-oriented, and phenomena-first approach.
“Again, whenever there is plainly some final end, to which a motion tends should nothing stand in its way, we always say that the one is for the sake of the other; and from this it is evident that there must be something of the kind, corresponding to what we call nature” (ibid).
Overall teleology always has to do with tendencies, not absolute determinations. He begins to wrap up this introduction by giving another example of the hypothetical necessity whose concept he pioneered.
“For if a piece of wood is to be split with an axe, the axe must of necessity be hard; and, if hard, must of necessity be made of bronze or iron. Now in exactly the same way the body, since it is an instrument — for both the body as a whole and its several parts individually are for the sake of something — if it is to do its work, must of necessity be of such and such a character, and made of such and such materials.”
“It is plain then that there are two modes of causation, and that both of these must, so far as possible, be taken into account, or at any rate an attempt must be made to include them both; and that those who fail in this tell us in reality nothing about nature” (p. 999).
Again, the two modes here are “that for the sake of which” and the phenomena associated with generation. Considering either of these in isolation yields an incomplete understanding, as we see respectively in bad scholasticism and bad empiricism.
“The reason why our predecessors failed to hit on this method of treatment was, that they were not in possession of the notion of essence, nor of any definition of substance. The first who came near it was Democritus, and he was far from adopting it as a necessary method in natural science, but was merely brought to it by constraint of facts. In the time of Socrates a nearer approach was made to the method. But at this period men gave up inquiring into nature, and philosophers diverted their attention to political science and to the virtues that benefit mankind” (ibid).
Socrates and Plato initially pioneered the notion of “that for the sake of which”, but in turning away from the phenomena of generation and becoming, they gave it a somewhat one-sided character.
The subtle way in which Aristotle wields the concept of essence avoids treating it as an absolute, or as something strictly univocal. In any given context, there is a clear relative distinction between essence and accident, but the distinction is not the same across all contexts. Hypothetical necessity provides the mechanism by which what is “accident” at one level of analysis can be incorporated into “essence” at another level. (See also Hermeneutic Biology?; Aristotelian Causes; Secondary Causes; Aristotle’s Critique of Dichotomy; Classification.)