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.