Unlike his forbears, Aristotle’s theory of perception in his de Anima reveals a helpful sensitivity to four aspects in the act of perception: the causal, psychological, phenomenological, and epistemic.
This essay aims to elucidate Aristotle’s basic account of perception, and to evaluate his framework. I argue that his account offers a useful and nuanced framework for understanding the nature of perception in both animals and humans, the causal processes involved in perception, and its role in constructing knowledge.
§1 outlines and elaborates on Aristotle’s account of perception. §2 first commends its broadness and sensitivity, and then demonstrates its abiding usefulness as an account for perception.
§1 Aristotle’s Account of Perception
To define perception, Aristotle sought to discover the properties that distinguished beings with perceptual capacities, such as animals, vis-à-vis those without, such as plants (413b1-9). These properties are set forth in three discrete but interdependent conditions:
A subject, S, perceives a perceptible object, O, if and only if
- S possesses a perceptual capacity (defined as “what can receive the perceptible forms [of the object O] without the matter [i.e., the material components of O]” (424a17-18));
- S undergoes “a sort of alteration” (416b34) when, using his perceptual capacity, S receives the perceptible form of O without the matter (424a17-18); and
- S’s perceptual capacity “is made like [the perceptible object], and is such as it is” (418a4-5), such that the perceptual capacity and the form become isomorphic in a relevant way.
To explicate each, let us suppose the perceptible object O has the form of redness.
Consider criterion (i) in the context of a human eye’s interaction with the colour red. When one is said to perceive redness in an object, there is no obvious material transference of redness onto the eye itself because the eye does not turn visibly red. The human eye, then, receives the form of redness akin to how a “wax receives the seal of the signet-ring without the iron or the gold” (424a19-20): it identifies the object as having the form of redness without its matter.
The same cannot be said of plants. If plants have any perceptual capacities, then it would likely stem from the leaves, branches, or the plant axis. The only way these “perceptual” organs are obviously affected by redness is if one smeared red paint on them, or if the plant is placed in red water for its transpiration. They are thus “affected [by the form] along with the matter” (424b1-2), the redness along with the material medium of paint or water. Plants, then, fail to meet criterion (i).
Now for criterion (ii): the kind of alteration in animals is sui generis compared to plants and all other objects. In the latter, alteration is the process in which they are “affected and moved [in way F, where F denotes the object’s perceptible form] by an agent that is actively F” (417a16-17) and this involves “a sort of destruction of something by its contrary.” (417b1-2)
To see this more concretely, let F be redness, and consider how plants undergo alteration in terms of redness. When a potentially red tulip actualises redness, it entails a material (e.g., red paint) and an efficient cause (e.g., a painter) to paint the tulip red, and this destroys the contrary: the tulip’s native non-redness.
But the alteration of the perceptual parts in animals is sui generis in that it is “a distinct kind (genos) of alteration” (417b6-7), for “it is rather the preservation of what is potentially [F] by what is actually [F]” (417b3). Employing again the example of the human eye before a red object, the eye alters from being potentially red to actually red, but without the perpetual erasure of non-redness (hence “preservation”) nor the literal action of material and efficient causes on the eye. The eye, thusly, can perceive redness from one moment and not in the other, without the need for any material transference of redness or an agent actively transferring that redness. Unlike plant organs, therefore, the eye’s modality is fundamentally different. It is uniquely in hexis—“as potential, on the one hand, and as active, on the other” (417a11-12)—which renders the eye actively responsive to the perceptible forms more than the tulip’s entirely passive potentiality to alter.
Last is criterion (iii), which comprises two elements: alongside the reception of matter-less form in (i), there is a material aspect in the sequence of events leading to perception, namely, when “[c]olour sets in movement what is transparent, e.g. the air, and that, extending continuously from the object of the organ, sets the latter in movement.” (419a13-15)
For perception to occur, there must be a material aspect in its causal process. This process begins with the perceived object’s physical presence, and its perceptible form setting in motion (417a6-7), through the imperceptible medium, a series of physical events that alters the sense organ in two concurrent ways. These two ways are: first, a physical change in the organ itself, such that the organ exemplifies and reflects that change (e.g. “the air [making] the eye-jelly such-and-such” (431a16)), and second, a “mental” (Brentano 179) change, in which the perceptive part of the soul registers and represents the qualitatively identical form which is then recognised by “the general faculty of sense” (431b5), distinct from each sense-organ, but which unifies and tracks the changes in each (425a27-b4).
Since there is both a physical and mental aspect to perception, then the perceptual capacity and the object’s perceptible form are isomorphic: the changes to the sense organ and the general faculty of sense map symmetrically onto each other as physical and mental, body and soul.
§2 Aristotle’s Account Evaluated
Aristotle’s general account of perception far surpassed his contemporaries in its sensitivity to causal and psychological processes. Perception concerned Plato only insofar it acquired knowledge (Gulley 106). Democritus fared better by concluding that perception is caused by the object’s “emanations” (Laks 264) to the sense organ, but he missed the inner workings of the percipient’s physical sense-organ and mental states (419a15-21). Only Aristotle’s framework showed sensitivity to the physical and mental elements causally interlinked in perception. That modern accounts of perception reflect the same sensitivity attests to Aristotle’s persisting relevance.
Some may charge Aristotle’s account of mental states arising from perceptual experience as naïve by modern standards, however. For instance, Aristotle deems certain perceptions “about which we cannot be deceived.” (418a11-12) But perceptual deceptions and distortions are common, for instance, in psychological factors like selective attention. Before charging Aristotle with ignorance, however, the interpreter of Aristotle should proceed more carefully. He did qualify that the sense “may err as to what it is that is coloured or where that is” (418a16-17) which clearly admits perceptual error. Aristotle seems to think, then, that certain perceptual experiences are indubitable, while others are.
A harmony can be found in this apparent contradiction. While a perceiver may be deceived or uncertain about what object is red and where that object is, she may be certain that she is perceiving redness. In other words, the content of her experience of red can be true to her mind’s eye even if the actual object is not red; about this she “cannot be deceived.” (418a11-12) But her perceptual ability to organise and structure patterns of this redness and other factors into a recognisable whole (e.g. a red apple, the “what it is that is coloured”), to judge proximity (the “where that is”), and by extension other similar mental inferences besides the irreducible likeness of redness, can be incorrect. There is thus no contradiction.
Aristotle’s careful distinction between registering colour and mental inferences, though disputable, nevertheless brings conceptual clarity that remains useful in contemporary debate on the phenomenology and psychology of perception, which cares for such careful distinctions (Hatfield; Smith).
Furthermore, Aristotle’s account of perception succeeds in presenting a unified natural theory for explaining animal and human perception. Earlier attempts, by comparison, seem imbalanced and unintuitive because they tended either towards materialism, reducing perception to purely physical movement (Berryman), or dualism, relegating perception to bodily function separated from the mind, and hence without much epistemic value, a mental judgment (Taylor 449). But Aristotle’s hierarchal model unifies animal and human perception because it explains how they rely on an identical mechanism, and yet how human perception uniquely leads to knowledge.
This identical mechanism is the appetitive or desiring capacity of the soul, and its relation to the perceptual as the cause for motivation. Animal and human perception is often associated with recognising an “object of desire” (433a17) such as food, which induces desire in the creature, and “causes movement” (433a22) towards it. This inducement arises because the isomorphism of the ‘mental’ aspect with the food’s form (as in §1(iii)) is registered by the soul through the rudimentary capacity for imaging “appearance[s]” (428a2), which “urges” (433b7) it towards the food. Crucially, this account does not require an animal soul to have a propositional attitude such as “food is good” but merely an instinctual mechanism that urges the animal through its senses. This capacity is also shared by humans, for the smell of food likewise produces an identical urge to consume it.
Additionally, this model delineates how human perception is compatible but different from animals. Humans alone possess an additional “believing part” (413b29) or “reason” (433b5) which, more than imaging appearances, enables higher-order abilities such as understanding. If the food is unhealthy, for instance, the dog would still be moved by desire to consume it; whereas humans, though moved by the same desire, have “understanding [that] urges us to hold back” (433b6-7) in that a human is able to abstract, from the perceptible form of the food, its imperceptible potential to cause ill-health. This abstraction implies a sophisticated level of mental activity that discerns not just physical, concrete forms (e.g. edible flesh), but also imperceptible, abstract ideas (e.g. the unhealthy), which issues in propositional attitudes (e.g. the judgement that “this flesh is unhealthy”). Crucially, this capacity explains the knowledge construction process in humans, as abstract ideas learned through the perception of forms constitute the basis for apprehending and comparing other associated forms; hence, “no one can learn or understand anything in the absence of sense” (432a3). Aristotle’s empiricism and his account of perception still presents an influential theory of knowledge and learning.
Conclusion
To modern eyes, Aristotle’s original account of perception—with hylomorphic analyses of matter and form, body and soul—may appear obsolete. Recast into modern categories, however, his framework reveals careful attention to the nuances involved in human perception and perceptual experience, while retaining its coherence with his general account of animal perception. As the history of ideas, and contemporary developments attest, Aristotle’s framework remains of “enduring value” (Caston 48).
Works Cited
Aristotle. “De Anima”. Translated by C. D. C. Reeve, Readings in Ancient Greek Philosophy: from Thales to Aristotle, edited by S. Marc Cohen, Patricia Curd, and C. D. C. Reeve, Hackett, 2016, pp. 512-529.
Aristotle. “On the Soul”. Translated by J. A. Smith, The Complete Works of Aristotle: The Revised Oxford Translation, Volume One, edited by Jonathan Barnes, Princeton University Press, 1984, pp. 641-692.
Berryman, Sylvia. “Ancient Atomism.” The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Stanford University, Winter 2016, https://plato.stanford.edu/archives/win2016/entries/atomism-ancient/. Accessed 20 Nov. 2021.
Brentano, Franz. Psychology from an Empirical Standpoint. Translated by Antos C. Rancurello, D. B. Terrell, and Linda L. McAlister. Edited by Oskar Kraus and Linda L. McAlister. 1874. Routledge, 1995.
Caston, Victor. “Perception in Ancient Greek Philosophy.” The Oxford Handbook of Philosophy of Perception, edited by Mohan Matthen, Oxford University Press, 2015, pp. 29-48.
Gulley, Norman. Plato’s Theory of Knowledge. 1962. Routledge, 2013.
Hatfield, Gary. “Sense Data.” The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Stanford University, Fall 2021, https://plato.stanford.edu/archives/fall2021/entries/sense-data/. Accessed 17 Nov. 2021.
Laks, André. “Soul, sensation and thought”. The Cambridge Companion to Early Greek Philosophy, edited by A. A. Long, Cambridge University Press, 1999, pp. 250-270.
Smith, Joel. “Phenomenology”. The Internet Encyclopedia of Philosophy, edited by James Fieser and Bradley Dowden, https://iep.utm.edu/phenom/. Accessed 17 Nov. 2021.
Taylor, C. C. W. “Plato’s Epistemology.” The Oxford Handbook of Plato, edited by Gail Fine, 2nd ed. Oxford University Press, 2019, pp. 429-454.
Written by:
Chung Jiajun
Edited by:
Bernice Soh
The Nanyang Philosophy Review 