Aristotle on Perception

Real and meaningful analytic distinctions in experience such as activity and passivity need not be grounded in ontological dualities.

It is common to hear Aristotle summarized as asserting a monolithic passivity in processes of perception. This is a considerable simplification. What is true is that in the absence of something perceptible that does not depend on us for its being, Aristotle would say we have a case not of perception but of something else. This does not mean there are not many active dimensions to typical sense perception as well.

One of Aristotle’s deepest principles involves a recognition of profoundly mixed conditions as being more typical of real life than monolithic or homogeneous ones. Plato treats “mixture” as a first-class topic at the heart of what Aristotle would call first philosophy, and not as a mere derivative from “pure” concepts.

Later authors have often tended to downplay Plato and Aristotle’s emphasis on mixed cases in experience as normal, and instead to privilege pure “black and white” distinctions. I think we should if anything privilege the mixed cases, and demand evidence when confronted with claims that any real-world cases involve “pure” black-and-white distinctions.

Aristotle’s account of perception in book 2 of On the Soul relies mainly on descriptions expressed in terms of actuality, potentiality, and actualization. While it is true that actuality has a character that is mostly active and potentiality has a character that is mostly not active, it is once again an oversimplification to simply equate actuality with activity and potentiality with passivity.

Aristotle’s description of perception is deliberately abstract, which reduces the need to speculatively fill in missing details. Perhaps the most salient overall aspect of this account is that it involves a multi-leveled layering of actuality and potentiality and of active and passive aspects that may be only analytically distinct. He focuses very generally on the various requirements of the kinds of form involved, and works hard to avoid causal explanations not clearly grounded in evidence.

It is very characteristic that Aristotle treats perception and whatever is perceptible in a single context. For instance, his discussion of light occurs here. He has no theory of the transmission of light, which was only experimentally demonstrated in early modern times. In the absence of evidence to the contrary, he sees light as instantaneously diffused through a medium, and reasons that the medium must therefore play a necessary role in perception. For him, light is “the being-at-work of the transparent as transparent” (On the Soul book 2 ch. 7, Sachs trans., p. 101). “By transparent I mean what is visible but not visible in its own right, to put it simply, but on account of the color of something else…. Light is a sort of color of the transparent, whenever it is at-work-staying-transparent by the action of fire or something of that kind…. What, then, the transparent is, has been said, and what light is, that it is not fire or any body at all, nor anything that flows out of any body…, but the co-presence of fire or any such thing in the transparent” (ibid). “Rather, the color sets a transparent thing, such as air, in motion, and by this, if it is continuous, the sense organ is moved” (p. 103).

It is important to recognize that this is a thoughtful interpretation of ordinary experience, with minimal assumptions. We would say, e.g., that light is transmitted at the speed of light rather than instantaneously diffused, but this can only be justified by complex empirical evidence. We associate colors with particular wavelengths of light, and we think of light as consisting of material waves (or alternatively, particles of a particular kind) that cannot be directly observed, but all this depends on complex evidence and test equipment. By contrast, Aristotle aims mainly to do justice to our ordinary experience of seeing things — a dog, a rose, a landscape, and so on. He seems to think of the air in the presence of light as metaphorically “charged” with sensible forms, such that there is a continuous translation of visible configurations of color through the air along each perspectival line of sight.

He somewhat paradoxically speaks of a “transmission” of “forms without the matter” in perception, and of the soul-as-active-form-of-the-body “receiving” them. The soul, as an entelecheia (in Sachs’ translation “being-at-work-staying-itself”, or more literally “in [itself] end having”) of an organic body, is active at root. Perception is then at top level supposed to be the being-at-work of a receptivity of the primarily active soul. Since the “transmission” of color through the air is said to be without matter, it must be more like a translation of color between the medium and the eye.

Some contemporary writers have claimed that Aristotle’s account of perception is of historic interest only, sheerly on the ground that it focuses on potentiality and actuality rather than physical causes. But as usual, Aristotle is far more interested in interpreting experience in meaningful ways, with as few assumptions as possible.

I think it is better to have a very abstract description that remains descriptive of experience, rather than imaginatively positing physical or physiological explanations. That is to say, it is better to be only abstractly descriptive but faithful to ordinary experience like Aristotle, than it is to have a more physically grounded explanation like the Stoics, at the cost of depending on additional assumptions of fact that turned out to be wrong in light of more detailed empirical investigations.

The Stoic theory — following the general Stoic precept that everything that has being must be some kind of body — seems to involve a kind of subtly material forms of objects invisibly but literally flying through the air as distinct wholes, ancestral to the medieval “sensible species”. This is a logically consistent physical and physiological account, which however makes numerous speculative leaps of the sort Aristotle aimed to minimize.

The mathematicians Euclid and Ptolemy geometrically analysed properties of light rays, but believed light rays were actively emitted by the eye, rather than received by it.

The “father of modern optics” and early contributor to scientific method, Iraqi polymath Ibn al-Haytham (ca. 965-1040 CE), known to Latin readers as Alhazen, was the first to explain that vision occurs when light reflected from objects passes to the eye, and to assert that the brain plays a major (active) role in the process of identifying objects. His work was taken up by Roger Bacon, Robert Grosseteste, Leonardo da Vinci, Galileo, Huygens, Descartes, and Kepler, among others.

The reception of light in and of itself is passive, but ordinary seeing has a large cognitive and interpretive dimension, whether considered at the level of events in the brain or at the level of an interpretation of meaningful content. Reception of light rays is passive, but even the most minimal identification of objects cannot be entirely passive.

The visible forms of patches of color that are diffused through the transparent medium in Aristotle — just like the reflected light in the modern account — are indeed passively received, but that no more makes the entire process of vision necessarily passive in Aristotle than it does in the modern account.

“But about all sense perception in general, it is necessary to grasp that the sense is receptive of the forms of perceptible things without the material, as wax is receptive of the design of a ring without the iron or gold…; and similarly the sense of each thing is acted upon by the thing that has color or flavor or sound, but not in virtue of that by which each of those things is the kind of thing it is, but in virtue of that by which it has a certain attribute, and according to a ratio” (book 2 ch. 12, p. 118).

Joe Sachs comments in a note that “Some of the difficulty can be avoided if one keeps in mind that, by form, Aristotle does not mean shape or appearance. In the Platonic dialogues, it is always emphasized that the eidos is not the mere look of a thing…. That to which one must look, according to Aristotle, is the being-at-work of the thing. It is, then, no part of the analogy Aristotle intends with the wax impression, that the eyeball, say, becomes shaped and colored like an olive when it looks at one. What it takes on must be some sort of active condition” (p. 118n, emphasis added).

This last point about the active condition, I think, is the import of Aristotle’s phrase in the above quote, “not in virtue of that by which each of those things is the kind of thing it is, but in virtue of that by which it has a certain attribute, and according to a ratio”. We do not directly perceive the kinds of things we perceive, but rather “that by which [things have] a certain attribute, and according to a ratio”. I take this to be a suggestion of what should or should not count as a “perception”.

There is a puzzle here about how “that by which” a thing has an attribute would count as perceptible. I would argue that if this kind of abstraction does count as perceptible in some way, that would be another indication that perception is not entirely passive. Aristotelian “perception” would then be quite rich, including many things I have been calling products of the Kantian synthesis of imagination. But it would still stop short of, say, directly apprehending a complex gestalt or whole “image” as an immediately intelligible unit.

Worries about “passivity”, it seems to me, ought to be directed mainly at the kind of claims of direct apprehension of complex images as meaningful wholes that Aristotle explicitly rules out in this passage.

“But ‘being acted upon’ is not unambiguous either…. For the one who has knowledge comes to be contemplating, and this is either not a process of being altered (since it is a passing over into being oneself, namely into being-at-work-staying-oneself), or is a different class of alteration” (p. 98).

“Being-at-work perceiving is described in the same way as contemplating, but differs in that the things that produce the being-at-work of perceiving are external, the visible and audible things, and similarly with the rest of the senses. The reason is that active perception is of particulars, while knowledge is of universals, which are in some way in the soul itself. Hence thinking is up to oneself, whenever one wishes, but perceiving is not up to oneself, since it is necessary that the thing perceived be present. And similarly too, even the kinds of knowing that deal with perceptible things are not up to oneself, and for the same reason, that the perceptible things are among particular, external things” (book 2 ch. 5, pp. 98-99, emphasis added).

I note first of all the explicit reference to “active perception”. Second, it makes perfect sense that “the kinds of knowing that deal with perceptible things are not up to oneself” — that in some way sensible things are what they are, independent of us, in a way that abstractions and universals are not. Aristotle even seems to think there is an at least abstractly identifiable level at which the particular senses cannot be deceived.

“[T]he means by which we live and perceive is meant two ways, as is the means by which we know (by which is meant in one sense knowledge but in another the soul, since by means of each of these we say we know something)” (book 2 ch. 2, p. 87).

“And neither is thinking the same as perceiving, for in thinking there is what is right and what is not right, … for sense perception when directed at its proper objects is always truthful, and is present in all animals, but it is possible to think things through falsely, and this is present in no animal in which there is not also speech” (book 3 ch. 3, pp. 133-134).

Here he explicitly bounds the analogy between perception and thought. We have already seen that perception for Aristotle is not entirely passive, so thinking, as something that is more up to us, must be less passive than that.

“And it is certainly not the reasoning part, or intellect in the way that word is used, that causes motion, for the contemplative intellect does not contemplate anything that has to do with action…. And even when the intellect enjoins and the reasoning part declares that something is to be fled or pursued one does not necessarily move, but acts instead in accordance with desire, as does one without self-restraint…. But neither is it desire that governs this sort of motion, since self-restrained people, even when they desire and yearn for something, do not necessarily do those things for which they have the desire, but follow the intellect” (book 3 ch. 9, pp. 152-153).

Later he specifies that the motion mentioned here is motion with respect to place, i.e., bodily movement, not anything directly associated with perception or thought. Comparatively speaking, the earlier “motion” of air in the presence of light was said in a different, more figurative way. We should not assume that the way activity and passivity apply in the one context is the same as in the other.

He continues, “But it is obvious that these two things [together do] cause motion, desire and/or intellect, since many people follow their imaginings contrary to what they know, and in other animals there is no intellectual or reasoning activity, except imagination. Therefore both of these are such as to cause motion with respect to place, intellect and desire, but this is intellect that reasons for the sake of something and is concerned with action, which differs from the contemplative intellect by its end…. So it is reasonable that there seem to be two things causing the motion, desire and practical thinking, since the thing desired causes motion, and on account of this, thinking causes motion, because it is the desired thing that starts it. So it is one thing that causes motion, the potency of desire” (book 3 ch. 10, pp. 153-154, emphasis added).

What Aristotle initially mentions as “obvious” is refined and corrected later in the chapter. This sort of thing is very common in Aristotle. In book 2 chapter 2, he says that “what is clear and more knowable by reason arises out of what is unclear but more obvious” (p. 84).

“[B]ut the potency of desire is not present without imagination, while all imagination is either rational or sensory” (p. 156).

The imagination is identified in Aristotle’s On Memory and Recollection as the root of all perception. Here he suggests that it also depends on the particular senses. Both could easily be true if the sense in which imagination is the “root” of perception is teleological, rather than causal in the modern sense.

“For imagination is different both from perceiving [by the particular senses] and from thinking things through, and does not come about without perception, and without it there is no conceiving that something is the case” (book 3 ch. 3, p. 134).

Aristotle is saying that while conceiving that something is the case depends on imagination and imagination ultimately depends on the particular senses, we never directly perceive that something is the case. That something is the case is a practical judgment about particulars, rather than a perception. “Thinking things through” (dianoia) is discussed separately from pure thought or intellect (nous), and is a rational activity of the soul grounded mainly in imagination. To really “occur” in a human, pure thought depends on the activity of thinking things through as its vehicle.

“[F]alsehood is always in an act of putting things together…. What makes each thing be one is intellect” (book 3 ch. 6, p. 144). “[B]ut thinking what something is, in the sense of what it keeps on being in order to be at all, is true, and is not one thing attached to another” (p. 145).

Here he seems to be emphasizing that the idea of what something truly is, in the sense of being-at-work-staying-itself, is not adequately expressible in terms of a simple combination of pre-existing parts or independently defined features. Also, no expression of a “what” by itself forms an assertion that could then be either true or false. A “what” by itself has more of the character of a definition that could be either accepted by hypothesis or considered hypothetically.

If the thought of a being-at-work-staying-itself is simply “true”, it seems to me it must be true in some sense other than correspondence — perhaps a being-true-to-itself through coherence. This use of “true” is also different from the way it is defined in On Interpretation, where truth and falsity are said to apply if and only if we say something about something, which means a “what” taken in isolation would be neither true nor false. Only what is said about the what could be true in that sense, but then it could also be false, depending on what is said. So “true” is being said in a different, special way here.

“Knowledge, in its being-at-work, is the same as the thing it knows, and while knowledge in potency comes first in time in any one knower, in the whole of things it does not take precedence even in time, for all things that come into being have their being from something that is at-work-staying-itself. And… the perceiving thing is not [merely] acted upon nor is it altered. Hence this is a different kind of event from a motion” (book 3 ch. 7, pp. 145-146, brackets in original, emphasis added).

Here he emphasizes a distinction between motion in the primary sense of ordinary bodily motion on the one hand, and the actualization of a potential on the other, identifying perception with the latter.

Aristotle on Explanation

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.)

Russell on Causality

Bertrand Russell (1872-1970) was one of the founders of analytic philosophy. His contributions to mathematical logic, philosophy of mathematics, and philosophy of language were highly influential, and he wrote on a host of other topics as well. In a famous 1912 essay “On the Notion of Cause”, he addressed the common prejudice that I have been referring to vaguely as “causality in the modern sense”, and argued that modern science does not in fact rely on it. I support this conclusion.

According to Russell, “the word ’cause’ is so inextricably bound up with misleading associations as to make its complete extrusion from the philosophical vocabulary desirable” (Mysticism and Logic, p.180). “In spite of these difficulties, it must, of course, be admitted that many fairly dependable regularities of sequence occur in daily life” (p. 187).

The idea of the supposed “law of causality” is that the same causes always produce the same effects. Russell points out that the alleged necessity with which one “event” is said to follow another depends on an abstracted notion of repeatable “events”, but every concrete event implicitly involves such a vast amount of individualizing detail as to be essentially unrepeatable.

“What I deny is that science assumes the existence of invariable uniformities of sequence of this kind, or that it aims at discovering them. All such uniformities, as we saw, depend upon a certain vagueness in the definition of the ‘events’…. In short, every advance in a science takes us farther away from the crude uniformities which are first observed” (p. 188, emphasis added).

Behind such presumptions of uniformity lies the prejudice that a cause somehow compels a particular effect. “What I want to make clear at present is that compulsion is a very complex notion, involving thwarted desire. So long as a person does what he wishes to do, there is no compulsion, however much his wishes may be calculable by the help of earlier events. And where desire does not come in, there can be no question of compulsion. Hence it is, in general, misleading to regard the cause as compelling the effect” (p. 190, emphasis added). “A volition ‘operates’ when what it wills takes place; but nothing can operate except a volition. The belief that causes ‘operate’ results from assimilating them, consciously or unconsciously, to volitions” (p. 191).

“[A]ny causal sequence which we may have observed may at any moment be falsified without a falsification of any laws of the kind that the more advanced sciences aim at establishing” (p. 194). “The uniformity of nature does not assert the trivial principle, ‘same cause, same effect’, but the principle of the permanence of laws” (p. 196). “In all science we have to distinguish two sorts of laws: first, those that are empirically verifiable but probably only approximate; secondly, those that are not verifiable, but may be exact” (p. 197).

“We cannot say that every law which has held hitherto must hold in the future, because past facts which obey one law will also obey others, hitherto indistinguishable but diverging in future. Hence there must, at every moment, be laws hitherto unbroken that are now broken for the first time. What science does, in fact, is to select the simplest formula that will fit the facts. But this, quite obviously, is merely a methodological precept, not a law of Nature” (p. 204, emphasis in original).

“We found first that the law of causality, as usually stated by philosophers, is false, and is not employed in science. We then considered the nature of scientific laws, and found that, instead of stating that one event A is always followed by another event B, they stated functional relations between certain events at certain times, which we called determinants, and other events at earlier or later times or at the same time…. We found that a system with one set of determinants may very likely have other sets of a quite different kind, that, for example, a mechanically determined system may also be teleologically or volitionally determined” (pp. 207-208, emphasis added).

I have suggested that scientific laws expressed in terms of equations are a specific kind of what Aristotle called formal “causes” (or better, formal “reasons why”). They are the kind that is expressible in mathematics. But natural or physical causes are still commonly conceived as efficient causes in the sense that this term acquired in late scholasticism, and it is this prejudice that Russell was addressing here.

The diverse compilation Aristotle’s early editors called Metaphysics (“after the Physics“) includes a summary of the four causes discussed in the Physics. Unlike other parts of the Metaphysics that, for example, discuss the term commonly translated as “substance” in far greater depth than in the Categories, the summary of efficient cause in the Metaphysics is less sophisticated than the discussion in the Physics. Thomistic and late scholastic notions of efficient cause seem to be based on the more simplistic account given in the Metaphysics, where the efficient cause is treated as more narrowly concerned with motion.

The Physics says very explicitly that the art of building, not the carpenter or the carpenter’s action, is most properly the “efficient cause” of the building of a house. The building of a house is implicitly considered as an end, not as a concrete motion. The art of building is the primary means by which this end can be successfully accomplished. This suggests to me that just as the “material cause” in Aristotle is hylomorphically paired with the “formal cause”, the “efficient cause” is related to the “final cause” as means are related to ends. Efficient cause as the means by which an end is realized is quite a bit different than, and more general than, the efficient cause as cause of motion that is the basis of the Thomistic and late scholastic concepts, as well as of the “modern” prejudice addressed by Russell.

Separate Substances?

One of the more difficult or troublesome aspects of the Aristotelian tradition for me is the notion of “separate substances”. Certainly this was greatly expanded by later writers, but it appears to have a basis in the texts we attribute to Aristotle.

A separate substance would seem to be something that at least does not participate in earthly matter, but in Aristotle there is some ambiguity whether separate substances are supposed to be completely free of matter, or just free of earthly matter. In Aristotle’s thought this makes a difference, because he regarded celestial matter as being fundamentally of a different kind than the earthly matter that is subject to generation and corruption. Conditioned as we are by theories of modern science, this may seem quaint to us, but it is a reasonable inference if we focus on ordinary human experience. In a similar way, Aristotle refers to the movements of the stars as “eternal”, on the practical ground that humans looking up from Earth do not observe them to change.

There is a more general point regarding eternity. Aristotle seems most often to use this term in the pragmatic way mentioned above. He calls things eternal if they are constant within human experience. This is quite different from the stricter sense of eternity, as meaning outside of time altogether. Plato’s geometrical objects and Augustine’s God, I think, are supposed to be outside of time altogether. Both the Aristotelian and the strict notion of eternity are different from the more popular religious sense of eternity as lasting forever. Medieval theologians coined a special word for the latter: “sempiternity”.

The separate intellect or intellects that Averroes talks about do not seem to me to be eternal in the strict sense of outside of time. At one point, Averroes says for example that while he assumes humans will always exist, if per contra humans became extinct, there would no longer be a material intellect. Aristotle had said that the potential intellect is nothing at all until it begins to think, and Averroes seems to say that humans provide the occasions for it to think. Having a dependency on temporal beings seems to me to be incompatible with eternity in the strict sense.

An even subtler question is how to regard the situation in which something strictly eternal is said to act as a final cause that is said to move something earthly. As noted in the last post, Aristotle regarded motion as something existing only in the thing moved. He distinguished “moved movers” from “unmoved movers”, but moved movers are moved by something other than themselves. For Aristotle, everything that is moved is moved by something else; there are no absolute by-their-bootstraps “self-movers”, although most or possibly all beings have some degree of activity of their own. So a moved mover is called that only insofar as it is moved by something else.

The preeminent movers in Aristotle are ends — not mechanical impulses, not generators of something from nothing, not “agents” of any sort at all. Ends have a kind of virtual existence or subsistence that could in principle be independent of any embodiment. They move us in the way that values move us. Aristotle suggests that even earthly matter is moved by ends in some rudimentary way — not that it has consciousness of its own, but that its being exhibits something analogous to preferences to being in one state rather than another. This is just what it is to “have a nature”. All Aristotelian natures have some involvement with ends in this way.