¹ Throughout the paper I use ‘aisthesis’, ‘perception’ and ‘sensation’ (and similarly their cognates) interchangeably. I do not think that Plato distinguishes sensation from perception. Four of the more important recent papers are those of Cooper, J., ‘Plato on Sense-Perception and Knowledge (Theaetetus 184–6)’, Phronesis 15 (1970), 123–46CrossRefGoogle Scholar; Burnyeat, M., ‘Plato on The Grammar of Perceiving’, CQ 26 (1976), 29–51CrossRefGoogle Scholar; Modrak, D., ‘Perception and Judgment in the Theaetetus’, Phronesis 26 (1981), 35–54CrossRefGoogle Scholar; and Frede, M., ‘Observations on Perception in Plato's Later Dialogues’, in Essays in Ancient Philosophy (Minneapolis, 1987), pp. 3–8Google Scholar. Frede's paper, though delivered in 1973, was only published as recently as 1987.

² By ‘concept’ I mean nothing very elaborate. Concepts are the mental analogues of words, the elements of the language of thought. The guiding force behind the notion that thought is language is that the aboutness or meaning of words and the aboutness or intentionality of thought are either the same relation or so closely connected that to understand the one relation is to understand the other. To the extent that elenctic and dialectical inquiry is at once the study of language, concepts and things, the investigation of concepts is capable of yielding knowledge of things.

³ If a capacity or faculty is prepositional, then its activity is marked by a judgment and that judgment is either true or false. The constituents of these judgments are concepts, one of which is being.

⁴ Virtually every Platonic dialogue says something about aisthesis. Besides the discussions in the Timaeus and Theaetetus, other important remarks on perception are found in the Republic, esp. 523–5 and 602–3Google Scholar, the Phaedo, passim, and the Philebus, 33c–39Google Scholar. I believe that the remarks in the Philebus are consistent with the account of the Timaeus, although there is no detailed analysis of the causes of sensation or the sensory process. As for the middle period dialogues, I believe that equally plausible cases can be made for and against the view that their account of perception is consistent with the Timaeus' account: cf. Burnyeat, art. cit. (n. 1). As to the date of the Timaeus, I think that it is a late dialogue.

⁵ 42b, e. The mortal part of the soul is never explicitly characterized as irrational (ἄλογον). Its capacities, pleasure, perception, etc., are so characterized. Since it is the seat of such capacities, and since its composition is totally unlike that of the rational soul, it is not illegitimate to describe it as the irrational soul. The later Platonists knew it under this description. That the irrational soul lacks the cognitive capacities had by the rational soul does not imply that it is without capacities. Somehow it is able to receive the movements from the sense-organs and then pass them on to the rational part of the soul.

⁶ Two features of this passage do have some impact on my topic. At 50a1–4 and probably at 52d4–e1 Timaeus mentions sensible qualities. The former suggests that there are Forms of such qualities. The latter indicates that these qualities, as they figure in the physical world, are π⋯θη of the more basic kinds of matter. They do not, pace Cornford, F. M., Plato's Cosmology (London, 1937), p. 198 n. 1, p. 199Google Scholar, comprise earth, air, fire and water. See Mohr, R., The Platonic Cosmology (Leiden, 1985), pp. 119–23CrossRefGoogle Scholar. If there are Forms of the sensible qualities, they of course will not be sensible. The instances of these Forms, the π⋯θη of triangles and bodies, are sensible. What is left open in this passage is how we are to understand the kind π⋯θη these qualities are.

⁷ cf. Williams, B. A. O., Descartes (Harmondsworth, 1978), passimGoogle Scholar; Nagel, T., ‘Subjective and Objective’, in Mortal Questions (Cambridge, 1979)Google Scholar; and McGinn, C., The Subjective View (Oxford, 1983), pp. 9–16.Google Scholar

⁸ Mohr adopts what he calls an ‘epiphenomenal’ interpretation of the sensible qualities. Sensible qualities are consequences of primary particles (p. 123 n. 26). Since Mohr is no especially concerned with sensible qualities, it is difficult to know what he thinks an epiphenomenal consequence is. Epiphenomenalism, traditionally construed, is a dualistic theory according to which mental events or properties are caused by physical events or properties but are themselves causally inefficacious. It is therefore odd for Mohr to claim that these epiphenomenal sensible qualities are motions (κίνησις). Since these motions have causal efficacy on souls (and matter?), they are not epiphenomenal. Modrak characterizes Plato's conception as ‘phenomenalist’ (pp. 35–41). On her account, the doctrine of the Timaeus is equivalent to th doctrine of the Twins stripped of its Heraclitean base. ‘On the phenomenalist theory, the objec that is grasped in perception, strictly speaking, does not belong to the extra-mental world, since its existence depends upon its being perceived’ (p. 40). The objects of perception, on this account, are, in effect, sense-data. Since sense-data exist only when perceived, they are subjective. By stripping away the Heraclitean base, Modrak strives to bring some objectivity to the production of these objects. Like-structured organs, such as the eyes of different humans and like-structured external bodies produce sense-data of the same kind (given that environmental conditions are the same). I infer from her analysis that sense-data have (are) their qualities absolutely. I see no evidence in Plato of anything like sense-data. I discuss the consequences of Modrak's interpretation in the last part of my paper.

⁹ cf. Taylor, A. E., A Commentary on Plato's Timaeus (Oxford, 1926), pp. 430–1.Google Scholar

¹⁰ Ibid., p. 430: ‘In the sensation itself we directly become aware of what he [Timaeus] holds to be the “objective” fact that our flesh is being lacerated or pierced by the “hot” body.… heat is a directly “sensed” object.’ Timaeus denies that we are directly aware of the laceration of the body. Whether heat as directly felt could be identical with the laceration of the body which is not directly felt is a thorny problem involving controversies about qualia, opacity and the nature of theoretical ‘reduction’. I am dubious that Plato ‘reduces’ anything to anything else.

¹¹ cf. Cornford, , op. cit. (n. 6), pp. 261–3Google Scholar: ‘…[T]he sense organ does play a part in making the hotness we perceive, and the fire is not hot save when perceived…The objects have dispositions or powers of producing sensation and hotness in conjunction with the organ’ (p. 261 n. 1).

¹² McDowell, J., Plato, Theaetetus (Oxford, 1973), pp. 137–40Google Scholar, thinks that the experience is not unique, except in so far as it is particular instances of the (same) quality that are brought into being in the act of perceiving. See also Modrak, , pp. 35–40Google Scholar. While it may be incredible, I think each set of parents and each set of offspring are unique. The Twins doctrine is designed to ensure that nothing is anything in its own right and that each parent is different from one moment to the next. My eye, at t₁, mixes with the log, at t₂, to beget whiteness and vision. These twin, fast motions cause my eye, now at t₂, to become a (white) seeing eye and the log, also at t₂, to become a white log. This second change guarantees that no object can remain the same so as to be a parent of two sets of offspring. If intercourse takes place at t₃ between some object and my eye, it will not be my eye simpliciter, but rather my white-seeing-eye that serves as the parent of the new offspring. It is important to notice that although parents and offspring come to be with respect to one another (πρ⋯ς ἄλληλα), the offspring themselves change by being born and then moving, whereas the parents change by giving birth and then becoming altered in quality. In the final refutation of Protagoras-cum-Heraclitus, Socrates will emphasize that whiteness and vision must themselves be changing in quality. He uses this fact to refute the position. Whiteness and vision are fast motions because they move in between the two parents. The parents are identifiable only after they have been changed by these fast offspring. Therefore, if these offspring are themselves changing in quality, i.e. have no quality to bequeath to the eye and log, none of the parents or offspring will be identifiable. See Burnyeat for a similar reading at least with regard to the uniqueness of the agent in each act of perceiving.

¹³ If we consider other dialogues, there are indications that there are Forms of the sensible qualities and even clearer statements to the effect that physical objects possess sensible qualities absolutely. See the Phaedo, especially 106Google Scholar, Cratylus 423eGoogle Scholar, Theaetetus 184–6Google Scholar, Meno 74c1–76e9Google Scholar, Republic 524; and note 8 above.Google Scholar

¹⁴ The objectivity and absoluteness of the quality licenses the claim that, at bottom, looking red presupposes something's actually being red. If there are no sense-data, and since Forms are not perceptible, it can only be the physical objects themselves that are red. Physical objects are red regardless of whether they are perceived or whether there are perceivers. On the other hand, to explain their ability to affect perceivers, one must introduce sense-organs and irrational souls. How red objects appear is, of course, only partly a function of their being red. The environmental conditions must be normal – though normality is hard to define – and the sense organs must be functioning properly – though that too is hard to define. Moreover, red may appear differently to creatures whose organs differ in structure from ours. None the less, from the demiurge's perspective, what red is and which objects are red is not affected by the difference in how red objects appear.

¹⁵ See Cooper and especially Burnyeat for a review of the various positions and of the debate over whether Plato alters his account of perception from the middle to the later dialogues.

¹⁶ cf. Burnyeat, , art. cit. (n. 1), 47–50Google Scholar. He says that Plato, in the Theaetetus, came to discover the notion of the ‘unity of the perceiving consciousness’, i.e. ‘…the notion of the unity of a single thinking and perceiving subject…’ (p. 50). The argument at 184–6 concerns that thesis: ‘But a confirmation, if not an explicit proof, of the unity thesis is implicit in something the argument does emphasize, that the soul can reason and think about whatever we perceive. For the soul's consciousness of things perceived would be unintelligible if it was not the same soul that perceived them but another subject or subjects’ (p. 47) (my emphasis).

¹⁷ In fact, there are two problems of interaction, one concerning how the material sense-organs interact with whatever aspect of the soul it is that perceives, and a second concerning how this non-judgmental, non-cognitive aspect of the soul interacts with the rational capacity. He solves neither.

¹⁸ Aristotle takes as primitive the power of the sensory soul to ‘take on the form of the sensible without the matter’ and then invokes phantasmata as an intermediary, in some sense, between sensation and thought. The medievals debated whether it was through ‘illumination’ or ‘abstraction’ that sensory information was acquired by the intellective soul from the sensory soul. Descartes dispensed with the ‘sensory soul’ and turned perceptions into judgments of the single res cogitans (thereby creating a whole new set of problems). For modern accounts of the difficulties, see, e.g. Fodor, J., The Modularity of Mind (Cambridge, 1983)Google Scholar, and Dretske, F., Knowledge and the Flow of Information (Cambridge, 1981).Google Scholar

¹⁹ Burnyeat brilliantly analyzes the difference between the dative of means and the dia idiom and the nuances of the dia idiom. The uncertainty about what perceives is supposedly eliminated by Plato's discovery of the unity of the perceiving consciousness, though Burnyeat concludes in the end that perception is a hard-to-characterize activity of this single soul.

²⁰ cf. Cooper and Burnyeat, who uses the phrase ‘features of objects’. What a feature might be is wisely left unspecified, since it may range from a sensible quality to an essence, and perhaps may include relational properties or second-order properties.

²¹ On the assumptions that, for Plato, knowledge is of essences and that essences are discovered by dialectical or philosophical inquiry of some sort.

²² cf. Frede. On my use of ‘concept’ see note 2 above. I do not think that concepts are to be found apart from judgments, nor do I think that judgments are composed of non-conceptual elements and conceptual elements. I therefore discount the possibility, bruited by Cooper, that there is a level of conceptual activity ‘below’ judging (or thinking) such as naming or labelling. Plato does entertain the notion that there is naming apart from saying, e.g. at Sophist 262b-c and Theaetetus 201eff., but he never embraces the view. Even when he discusses sensible qualities, he uses demonstrative sentences to express the mind's cognition of them. See below note 48.

²³ cf. Burnyeat, , art. cit. (n. 1), 47–8Google Scholar. Cooper, (art. cit. (n. 1), 127)Google Scholar and Modrak, (art. cit. (n. 1), 35–40)Google Scholar come down on the side of the strong, restricted reading of the assumption. The commons are applicable to the objects of more than one sense, but that there be a plurality of senses is not necessary for their discovery or application. Were there a rational being with only one sense modality, the commons would be applicable to the objects of its sense, as 186b2–9 illustrates. Cornford, F. M., Plato's Theory of Knowledge (London, 1935), p. 105Google Scholar, and Cherniss, H., Aristotle's Criticism of Plato and the Early Academy, vol. 1 (Baltimore, 1944), p. 236 n. 141Google Scholar, think that the koina ‘are, in fact, the meanings of common names – what Plato calls Forms or ideas.’ Cooper, (art. cit. (n. 1), 128 n. 8)Google Scholar disagrees: ‘koina are predicates belonging to the objects of more than one sense.’ If physical objects are the objects of more than one sense, and if their names can be construed as predicates, then these qualify as koina on Cooper's account. See Modrak, (art. cit. (n. 1), 36–7)Google Scholar on Burnyeat's talk of ‘features of sounds and colours’. I want it both ways. Commons are concepts or predicates that apply to all objects, sensible and insensible alike. There are, however, concepts or predicates such as ‘white’ or ‘hard’ which, though not commons in the specific sense, are applicable to many objects of a single sense. Of course if physical objects are sensible, then these predicates would be commons in the specific sense.

²⁴ Provided that we can determine the membership of the class of sensibles. If the only sensibles, strictly speaking, are the special sensibles, then the critical issue is why we think that we can perceive so much else. Perhaps Plato, in the later dialogues, has a nascent notion of phantasia which might serve as part of the answer to this question. See Sophist 264aGoogle Scholar and Philebus 39–40.Google Scholar

²⁵ Burnyeat thinks that the sense of being (οὐσία) that sensibles have in their own right is to be understood in light of the work of Frede, M., Predikation und Existenzaussage (Hypomnemata 15; Goettingen, 1967)Google Scholar; Owen, G. E. L., ‘Plato on Not-Being’, in Plato I: Metaphysics and Epistemology, ed. Vlastos, G. (Garden City, 1970), pp. 223–67Google Scholar; and Kahn, C. H., ‘The Greek Verb “To Be” and the Concept of Being’, Foundations of Language, ii. 1966Google Scholar: ‘I take it to mean at least that there are values of F such that the colour or the sound is F’ (p. 44). I concur, though throughout the paper I talk of Being simpliciter. I want to leave open whether Being has only one sense here (and elsewhere in Plato). I believe that there are two senses of the notion, one concerned with essence and restricted to Forms, and one concerned with ‘having a property’ and characteristic of both Forms and particulars. Since I think that perception gets at neither kind of being, I refrain from pressing the issue. My talk of existence is not meant to suggest a third sense of being. Both Forms and particulars exist.

²⁶ Burnyeat, , art. cit. (n. 1), 47.Google Scholar

²⁷ But see Frede, (op. cit., n. 1 above), pp. 6–8.Google Scholar

²⁸ cf. Burnyeat, , art. cit. (n. 1), 48.Google Scholar

²⁹ Modrak, , art. cit. (n. 1), 36–7Google Scholar argues in a similar fashion, though she also thinks that the argument requires the strong Inaccessibility Assumption.

³⁰ There is no reason to think that the Protagorean would grant that being is not a perceptible feature. If appearances are appropriately propositional, and if being is given a properly relativized account, then we are, he will aver, aware of being in perception. Since all Protagorean appearances cited throughout the dialogue are propositional in form, when Plato commences the argument with the Inaccessibility Assumption, each sense's perception should be understood as propositional in form: ‘[This] sound is’ and ‘[This] colour is’. The assumption is used to illustrate most vividly that these are, ex hypothesi, two distinct appearances, the constituents of each supposedly relative to that appearance which they respectively constitute. It does not matter, as Burnyeat notes, which predicate completes the proposition.

³¹ Plato accepts at least a weak version of the Inaccessibility Assumption for reasons explored in the Timaeus. The material structure of a given individual sense is not receptive of the structured matter of the sensibles proper to another sense. Whether Plato accepts the strong version hinges on, among other details, whether the optics of the Timaeus enables him to say that shapes and sizes are perceptible.

³² This is recognized by Frede, Burnyeat and Cooper. Comparison and contrast are involved in concept formation. One needs to discriminate the colour from the background, distinguish it from other colours, note its recurrence, and so on. (This is not an ‘and so on’ to be taken for granted.)

³³ The position taken by Modrak and offered as a possibility by Cooper. The formula ‘implicitly contained’ is borrowed from Modrak, though the idea is not exclusive to her. Talk of what is ‘given’ is rampant throughout the history of philosophy. See Sellars, W., ‘Empiricism and the Philosophy of Mind’, in Science, Perception and Reality (New York, 1963).Google Scholar

³⁴ cf. Frede: ‘All questions are settled by the mind, though for some it does rely on perception’ (op. cit. (n. 1 above), p. 7)Google Scholar. Frede does not articulate what it is to rely on perception (any more than I do (or can)). For neither of us can it mean that it relies on some judgments that perception makes, for only the mind makes judgments. I suspect that he means that the mind uses what the individual thinks of as perceptual judgments, i.e. judgments about what we see, hear, taste.

³⁵ At least none of the ilk, for example, of Posterior Analytics B 19. The passages on recollection in the Phaedo and Meno, the discussion of what summons the mind in Book VII of the Republic, Philebus 33–40Google Scholar, and numerous others all concern activities of a soul that has already acquired concepts, i.e. already talks, thinks, and believes.

³⁶ The end result of our reflections on our beliefs and perceptions is knowledge of what there is. Talk of knowledge of concepts does double duty for both the Forms and the objects in the world the properties corresponding to these concepts qualify. I want to identify the concept that is known at least with the Form and perhaps with the instances of the Form. The former gives us the traditional objects of knowledge, the latter the possibility that there is knowledge of the external world. How concepts, or names, can apply to both the Forms, the instances of the Forms, and the particular bearers of those instances, is not discussed in this paper.

³⁷ It is arguable whether Plato thinks that there is a Form, Being Itself, let alone whether one could know it. Perhaps all that is knowable are the beings, e.g. Forms, and perhaps material particulars. Much turns on the way one reads the Sophist and what one thinks metaphysics, for Plato, is.

³⁸ See Theaetetus 189e4–190a6Google Scholar, Sophist 263d6–e13.Google Scholar

³⁹ So, for instance, we might give up our beliefs about what courage is, or justice, largeness, etc., and replace them with other beliefs. Or we might simply abandon a concept like ‘barbarian’ when we learn that the ‘cut’ does not yield a ‘kind’. Again, I repeat that concepts are just the mental analogue of words and are ‘of’ the same things to which words refer. It is of course terribly difficult to say what Plato thought words referred to, or how they refer to whatever they do. Concepts perhaps change when we learn that they do not refer to what we thought they referred to, and when we discover that they refer to what they do for reasons different from what we might once have thought.

⁴⁰ It is not the case that we acquire a concept as soon as we learn to say the word. Even as children we must practice using the language and learn when to use the word properly. It takes time to learn to say ‘Red’ or ‘This is red’ when in the presence of red objects.

⁴¹ cf. Cooper, , art. cit. (n. 1), 126Google Scholar. This is a fatal flaw in Cornford's. interpretation. It is prompted by his eagerness to find negative arguments for the Forms in the dialogue. Cooper rightly takes him to task for this.

⁴² cf. McDowell, , op. cit. (n. 12), p. 190.Google Scholar

⁴³ To acquire knowledge even of the sensibles involves much more than the comparison and contrast of sensations, or, more properly, perceptual judgments. The process probably does not differ greatly from that which is required to understand anything. There will be collection and division, elenctic examination of what people think and do, considerations of perspective, abnormal conditions and the nature of perception, and the locating of these concepts in a field of related concepts.

⁴⁴ See, for instance, Modrak, , art. cit. (n. 1), 44Google Scholar: ‘A simple perceptual judgment is an articulation of a state of affairs directly given in perception. It uses concepts that are implicitly given in sensuous representation. The explicitly held concept, although distinguishable from the implicitly given concept, is an articulation of the latter.’ Cf. Cooper, , art. cit. (n. 1), 141ff.Google Scholar

⁴⁵ I am uncertain as to when judgments are explicitly made and when implicitly made. It seems to turn on how familiar we are with the concepts we are employing, i.e. the subject matter we are judging, and how entrenched the judgment is in our web of beliefs. Since I think nothing is ‘given’ in perception, I think no judgments are implicit by nature or necessity. In claiming that perceptual judgments are not reflective, I mean that they do not take other judgments as their objects, or even into consideration as evidence.

⁴⁶ cf. Modrak, , art. cit. (n. 1), 42.Google Scholar

⁴⁷ ibid., p. 53 n. 15.

⁴⁸ cf. Modrak. How Russellian knowledge-by-acquaintance and sense-data came to figure in Platonic scholarship is a long tale. One of its roots can be traced back to Ryle, G., ‘Plato's Parmenides’, Mind n.s. 48 (1939), 129–51, 303–25CrossRefGoogle Scholar (see, for instance, pp. 36–7), and through him to Owen, 's paper ‘Plato On Not-Being’ (see, for instance, pp. 244–5)Google Scholar. The impetus was from thinking of knowledge of Forms in the middle period as roughly equivalent to knowledge-by-acquaintance and, concomitantly, thinking of the meaning of names as simple proxyhood. I do not think this is a fair representation of Plato's epistemology or theory of meaning. On the epstemological front, knowledge, throughout the corpus, is of definitions, i.e. of what x is.

⁴⁹ I would like to thank the Editors and the anonymous referee for invaluable comments on earlier versions of this paper. I would also like to thank Alan Code, Dan Farrell, Tony Long, George Pappas, Diana Raffman and Robert Turnbull for their constructive criticisms.