1. A Platonic Form, Whatever Else It is, is the Essence of Some Thing

The question to which the above supposition provides an answer is, essentially the following: What is a form? Forms are notoriously difficult to get a handle on in Plato. The proliferation of literature on this topic is a testament to Plato's lack of precision in articulating his theory of forms—if he does indeed have or articulate such a theory. In some dialogues forms are characterized as the things that fully or perfectly are, while in other dialogues, notably the Parmenides, the very nature and existence of forms is seriously problematized. Setting aside, for the moment, Plato's own criticism of the theory of forms and the very interesting and important questions about whether, at a later stage in his development, Plato radically revises the theory or even rejects forms entirely, let us look at the role that Plato ascribes to forms.

Toward the end of the Phaedo we find one of the few discussions in which Plato describes what we might call the forms in action. Here we find not merely an adumbration of the characteristics that distinguish forms from physical things but perhaps the clearest account of what forms are, what purpose they serve, and how they relate to physical things and properties. This account emerges out of a wider inquiry into the immortality of the soul. At this point in the dialogue Socrates has taken himself to have shown that the soul is stronger and more divine than the body, but Cebes has objected that this only shows that the soul is long-lived, not that it is positively immortal. To meet this objection, Socrates says, they must consider the nature of generation and destruction (95e7–96a4). This leads to a famous passage in which Socrates recounts the evolution of his thinking on these questions. What he is particularly interested in is coming to understand the explanations for certain phenomena; he wants to know the answers to a number of why questions concerning generation and destruction: Why do things come to be and perish? And why do they exist (96a8–10)?

It soon becomes clear, however, that his initial attempt to discover these explanations through what he calls natural inquiry (phuseôs historia) led him only to confusion. This confusion takes the form of an aporia about what could possibly serve as an adequate explanation. The sorts of explanations that Socrates initially pursued appealed exclusively to the physical constituents of things. For example, if one asked why a particular necklace is beautiful, a response might be that it is brightly colored. However, explanations of this sort fall foul of what is, for Socrates, a basic requirement of explanation. This requirement demands that there be consistency between an explanation and that which it explains. Thus, if there are two numerically distinct instances of the same phenomenon, then, according to this requirement, they must have the same explanation. That is to say, two instances of the same explanandum require the same explanans. Correspondingly, a single explanation cannot explain two numerically distinct, and contrary, phenomena: thus, same explanans, same explanandum (Socrates illustrates the validity of this requirement by considering a number of instances of its violation, see especially Phaedo 96e6–97b7). Regardless of what we think of the independent plausibility of this requirement, there can be little doubt that Socrates takes conformity with it to be essential to any adequate explanation (for a discussion of this requirement and the aporia it generates, see Politis [Reference Politis and Charles2010: 67–80]).

While mired in this aporia about explanation, Socrates tells us that he discovered the work of Anaxagoras who proposed that mind (nous) is the directing cause of all things. This view seemed to Socrates to be a promising solution to his aporia; for if mind truly directs everything, then all things will be oriented toward the good. Thus, if one wants to know why something is the way it is, then one need only look toward what is the best way for that thing to be (97c6–d1). However, Socrates's hopes of discovering these explanations in terms of the good in the work of Anaxagoras are dashed. After reading everything he could get his hands on, he finds that it is not mind that Anaxagoras appeals to in explaining phenomena, but air, water, ether, and the other constituent physical elements that had so dissatisfied Socrates as explanations before. To illustrate his disappointment, Socrates says that it is as if Anaxagoras had claimed that it is Socrates's mind that directs his activity, but that the explanation for his sitting in prison in Athens is that his body is composed of such and such bones, sinews, and muscles in such and such a state. An explanation of this sort is unsatisfactory for the very same reason that the earlier ones were—namely, it contravenes the requirement, same explanans, same explanandum. The fact that Socrates's body is physically constituted as it is could just as easily have explained a different state of affairs, one in which he had fled to a neighboring city in order to avoid execution. Importantly, however, Socrates does not dismiss the material conditions appealed to in Anaxagoras's explanations entirely; he acknowledges that these conditions are necessary for the situation to obtain, but he argues that, on their own, they fail as complete and sufficient explanations (99a4–7).

Having lost hope of finding someone who could adequately instruct him in the sorts of explanations that he so fervently desired, Socrates relates what he calls his second sailing, or his own attempt to discover a satisfactory form of explanation. As I shall explain in a moment, the procedure described in this inquiry involves positing certain essences corresponding to the properties or things in need of explanation—e.g., a just itself, a beautiful itself, etc. He then says that the explanation for a thing's possessing one of these properties is that it stands in some relation to the essence of that property.

This ‘safe’ schema of explanation, as Socrates calls it, satisfies the requirement of explanation described above (i.e., same explanans if and only if same explanandum) because, for example, the essence of beauty, the beautiful itself, explains why all and only beautiful things are beautiful and can never be the explanation for why something is not beautiful.

I am supposing that the sorts of things that Socrates posits here as adequate explanations are, basically, essences. That is to say, they are just what it is to be a certain thing or property; they are true answers to the Socratic-type question: What is F? Many critics (such as Sedley Reference Sedley1998) think that what Socrates is positing here, for the purpose of accounting for explanation, are forms: forms in contradistinction to essences. The idea that in this argument Plato moves straight to forms is common in the literature on this topic. It can be found in, at least, the following discussions: Taylor (Reference Taylor1969: 46–48), White (Reference White1981: 5–6, 44–45), Fine (Reference Fine and Graeser1987: 92–97), Rowe (Reference Rowe1993: 51–53), and Sedley (Reference Sedley1998: 127–32). The question that these commentators focus on is not whether the causes or explanations that Plato posits here are forms, but rather how best to understand Plato's introduction of what some have referred to as the formal cause. Such critics may or may not also think that forms are essences, but in any case they do not think that Plato's argument is simply for the conclusion that explanation is based in essences; they think his argument is for the conclusion that explanation is based in forms. This is an important issue of interpretation, if only because Plato's conclusion is significantly weaker if it is simply that explanation is based in essences than if it is that explanation is based in forms. This is because, on any interpretation, a commitment to forms is a commitment to more than simply essences. We may recognize the significance of this interpretative issue by observing that if Plato's conclusion is that explanation is based in essences, but not if his conclusion is that it is based, specifically, in forms, then this is a conclusion that Aristotle, or an Aristotelian more generally, can accept.

For the purpose of this paper, I am supposing that Plato's conclusion here is, precisely, that explanation is based in essences. Here I follow Politis (Reference Politis and Charles2010). The reason why I am content to make this supposition is that I take Politis (Reference Politis and Charles2010, section 2) to have shown that it is sufficient for the cogency of Plato's argument for the claim that the one and only way to secure that an explanation satisfies the requirement same explanans if and only if same explanandum, is to suppose that the conclusion of this argument is, precisely, that explanation is based in essences.

To be clear, it is not my intention to argue that in the Phaedo Plato thinks that the essences he identifies as adequate explanations are not forms or that they are essences in contradistinction to forms. For later in the argument, Plato associates these essences with, specifically, forms; that is, he says that they are forms, referring to them as eidê (103e3, 104c7). (The first reference to these explanations as forms comes at 102b1 and is put into the mouth of Phaedo; it is not until 103e3 that such a reference is put into the mouth of Socrates.) What this shows, on the interpretation that I am supposing, is that Plato at least in the Phaedo takes it that forms fulfill the explanatory role of essences. This is in conformity with the interpretative supposition that Plato's forms, whatever else they are in addition to being essences, are primarily essences. To accept this supposition is in no way to deny that there is more to Platonic forms than being essences, a point I shall draw upon later. The crucial point for my overall argument in this paper is that while Plato's reference to these essences as forms does indicate that forms fulfill the explanatory role of essences, it does not imply that all essences are forms. I shall take up this crucial point presently (section 2).

2. Plato's Basic Notion of Essence

Let me briefly recapitulate what I have argued so far. Toward the end of the Phaedo (95e–105c) Plato develops an account of explanation in terms of essence. This is put forward as a response to an aporia generated by the inability of traditional explanations, which appeal exclusively to the material constituents of things, to satisfy the stringent requirement same explanans if and only if same explanandum. According to Plato's alternative account, the explanation for why a thing x has a property f is that x stands in some relation to the essence of that property. That it is, precisely, essences that Plato is introducing here is confirmed a few lines later (101c3) when he uses the term ousiai to refer to these explanatory entities. It is only very late in the argument that Plato further associates these essences with the forms. This indicates that Plato is, in the first instance, interested in essences; it is the essence of a thing or property that explains why a thing is that thing or has that property, and it does so in a way that satisfies the stringent requirement of explanation. If this is correct, then it follows that forms, whatever else they also are, are the essences of a certain range of things and properties. This leaves open the possibility that there are also essences that are not forms.

In this section I begin by explaining what I take to be Plato's basic notion of essence. I elaborate the distinction that I have drawn between what I shall call form-essences and essences that are not forms. Finally, I clarify what is distinctive of form-essences and consider why Plato focuses on them to such an extent.

By essence I do not mean, and I do not think Plato has in mind, anything that should strike us or that would have struck Plato's contemporaries as puzzling or mysterious; all I mean by essences is that which is designated by a true answer to the Socratic question: What is F? This, as we all know, is the sort of question that occupies Socrates and his interlocutors in the early dialogues, and it remains central also in a number of dialogues generally thought to be from a later period (see, for example, Symposium: What is love? [ho Erôs, 200e8] and Theaetetus: What is knowledge? [hê epistêmê, 147b11]). I take it that what Plato is looking for in these inquiries is a general, unitary, and explanatory account of the what-it-is of a given thing or property (on the claim that Plato thinks that only an account that satisfies these requirements can adequately answer the ti esti question, see Politis [Reference Politis2015: 44–62]). It is clear, however, that such an account is not easy to give and that the requirements Plato imposes on an account—generality, unity, and explanatoriness—cannot be satisfied by anything less than a definition proper of the thing or property in question. What these discussions show is that for Plato a full account of the essence of a thing or property must be able to explain all and only instances of that thing or property. Thus, famously, Euthyphro's definition of piety as that which is loved by all the gods succeeds in its generality and unity, but it is ultimately unsatisfactory because it is unable to explain the connection between being pious and being god-loved (Euthyphro 9e1–11c6).

In the so-called dialogues of definition, therefore, Plato presses the idea that in order to specify the essence of a thing or property adequately one must ensure that that specification is, among other things, explanatory of all and only instances of that thing or property. This means that for those things and properties that have essences, the essences must be explanatory. From this we may infer that, for Plato, some explanation involves essences. In the Phaedo, on the other hand, Plato argues for the substantially stronger claim that all explanation requires essences. He does this, as we have seen, by specifying the criteria that must be met in order for something, anything, to count as a genuine explanation and then showing that these criteria can only be satisfied by an essence. Plato's strengthening of the claim that some explanation involves essences, to the claim that all explanation requires essences, is important in its own right, but it is also important because it shows that, for Plato, it is not the case that explanation in terms of essences is reserved for a special class of things. It shows, rather, that if one is to explain any thing, one must appeal to an essence.

If the above analysis is correct and what Plato offers in the Phaedo is an account according to which all explanation requires essences, then why does Plato associate these essences with forms? The answer to this question, I think, has to do with the sorts of things and properties that Plato is interested in explaining. Socrates's account of his intellectual autobiography demonstrates that traditional explanations in terms of material constituents are insufficient because they fail to satisfy certain requirements of explanation. Thus, if we take the property beauty, it is clear that an account of beauty specified solely in terms of physical attributes is not going to be adequate because those very attributes will cause one thing to appear beautiful and another to appear ugly or will cause the same thing to appear beautiful to one person and ugly to another. Thus, something distinct from the mere physical features of a thing is necessary to explain that thing's beauty in a way that conforms with certain basic requirements of explanation. The same is true of evaluative properties such as justice, virtue, and goodness and is also true of comparative properties, such as large and small. Things that possess these properties in one context will always appear in a contrary way in a different context despite their physical constituents remaining unchanged. In the dialogues, Plato frequently uses these kinds of properties to illustrate the general problem that has come to be called the problem of conflicting appearances (see, e.g., the discussion of the difference between the philosopher and the lover of sights and sounds at Republic 479a1–480a10). It is clear that for these kinds of things and properties, an essence specified in terms of physical constituents alone will never satisfy the requirement of explanation. For these things and properties a special kind of essence, a form, is required.

What is distinctive of these form-essences and what makes them particularly well suited to serve as the explanations for these troublesome properties is that they are nonphysical. That is to say, they exist apart from the physical things that display the properties of which they are the essences. In separating the form-essences from physical things, Plato indicates that they are not necessarily subject to the vagaries that plague physical things. Due to being nonphysical, the forms are exempt from some of the limitations that constrain physical things, qua physical. One of the crucial features that differentiates physical things from forms is perceptibility. As Plato frequently says, physical things and their attributes are apprehensible by means of the bodily sense organs, whereas forms are graspable solely by the mind through reasoning (see especially Republic 509d1–511e5, Phaedo 65a9–c10, and Timaeus 27d5–28a4). Just as their status as nonphysical entities exempts the form-essences from being subject to the alterations that physical things undergo, imperceptibility insulates the form-essences from the problem of appearing in contrary ways in different contexts—they do not appear, sensorily at least, at all.

Before we move on, it would be useful to say a few more words about the imperceptibility of forms; for, as mentioned, it is this attribute of forms that generates the inconsistency that has given rise to the question of this paper. I take it that the idea that forms according to Plato are imperceptible and are graspable only through reasoning is relatively straightforward, so I will not belabor it. In its defense I would like to call attention to two passages from the Phaedo and one from the Timaeus. In these passages Plato, as he typically does when he talks about forms, enumerates the general characteristics of forms in contradistinction to the general features of the physical things to which they are related. At Phaedo 65d–e Socrates elicits the agreement of his interlocutors that things like a good itself, a beautiful itself, and a just itself exist and that the interlocutors have never perceived these things with any of their bodily senses.

While this passage indicates that Socrates's companions have never seen the forms, it does not show that the forms are imperceptible, in principle. The claim that the forms are positively imperceptible comes several pages later. At 78c–d Socrates turns, as he says, to ‘the same things as in the previous argument’ and claims this time that these things, unlike the many physical things that share their names, cannot be seen, touched, or otherwise perceived—they are not only unseen but also invisible (ouch horata).

Here we have a clear assertion that forms, unlike the many beautiful things, the many equal things, and so on to which they are related, are unchanging and are cognized by reason and not through perception; they are, as Socrates says, unseen and unseeable.

This idea, namely, that forms are unseeable and, in general, positively imperceptible, is echoed in a passage from the Timaeus. At 51e6–52a4 Plato gives one of the few immediately recognizable arguments for the existence of forms. Here, he maintains that if true belief and knowledge are different, then it must be the case that forms exist.

This is a particularly nice passage because it starkly contrasts the general features of forms with those of physical things, and it is clear that perceptibility is crucial to this distinction. Plato mentions it no less than three times in the span of three lines: once in relation to the imperceptibility of the forms and twice in respect of the perceptibility of the things that participate in forms. It is clear, therefore, that perceptibility is a primary distinguishing feature, something that physical things have and forms do not.

These thoughts about the imperceptibility of forms are, of course, all quite familiar, but it is necessary to emphasize them here because, on the contrast that I am drawing between form-essences and essences in general, the former are distinctive because they possess this property, while the latter, as we shall see, are distinctive precisely because they do not.

What I hope to have shown in this section is that Plato introduces a special kind of essence—form-essence—for the purpose of explaining a certain range of properties. The tendency of these properties to appear in contrary ways in different contexts is what necessitates the postulation of nonphysical essences to explain them. (As mentioned above, the properties that I have specifically in mind here are evaluative and comparative properties [e.g., justice, beauty, large, small]. It is clear, however, that the scope of the form-essences is not limited to these, but also ranges over other properties [e.g., unity or oneness].) However, since the physical world comprises more than just these recalcitrant properties, it is still an open possibility that there are things and properties that can be adequately explained solely in terms of their physical constituents. The essences of these properties would, of course, be expected to satisfy the requirement of explanation—this is nonnegotiable—but they would do so in a way that does not necessitate the postulation of a separate, nonphysical and nonperceptible, form. For the moment I only intend to have argued that Plato leaves this possibility open; for he does not himself make any such distinction explicit. In the next section I will argue that the way in which Plato conceives of the essences of physical things and properties allows us to make the distinction, outlined above, on his behalf. The account that he develops of sensible qualities is particularly illustrative in this regard.

3. Sense Perception and the Knowledge of the Essences of Sensible Qualities

Let us return once more to the inconsistent tetrad with which we began this paper.

1. (1) a Platonic form, whatever else it is, is the essence of some thing (e.g., the form of the just is the essence of justice);

2. (2) for Plato those essences that are forms are imperceptible and are knowable through reasoning alone;

3. (3) one would reasonably expect that the knowledge of the essence of a particular color (e.g., red) requires and involves presentation with the relevant perceptible quality, red, hence requires sense perception; and

4. (4) if a sense perceptible quality has an essence, then that essence is a form.

The puzzle that these premises generate can be reformulated in the following way: If forms are essences and if forms are imperceptible, then what sense can be made of the idea of a form of a sensible quality? What would it mean to say that the essence of something like red—the what-it-is-to-be of red—is imperceptible? We are now, I think, in a position to offer a solution to this puzzle. As mentioned above, the solution I shall propose involves denying thesis (4) above, that is, it involves arguing that while sensible qualities do have essences, those essences are not forms. In order to defend this view, we must begin by considering what sensible qualities are according to Plato. Following Plato, I mean by sensible qualities those properties that are associated with the five bodily senses, that is, sounds, colors, tastes, textures, weight- and temperature-based qualities, and scents. Plato indicates that sensible qualities are limited to just these features at Theaetetus 184b8–185a3 and Timaeus 61d5–68d8. In what follows I shall argue that for Plato the essences of these properties can be specified entirely in terms of physical constituents and processes. I will then demonstrate that there is good textual evidence to support the view that this is not only the case for sensible qualities, but that it is also true of physical things more generally. Finally, I will address two potential objections to this view. The first concerns the issue of whether for Plato physical things in general and sensible qualities in particular have essences at all. For if they do not, then one can deny thesis (3), and the inconsistency becomes moot. There is good textual evidence, however, that Plato does think that sensible qualities have essences—that there is a what-it-is-to-be for things like colors and sounds. The second objection assumes a developmentalist reading of Plato and maintains that whereas at an earlier stage in his development Plato thought that the essences of physical things were, precisely, forms, at a later stage, and especially after writing the Parmenides, he comes to reject this view. In response to both of these objections, I shall demonstrate that in the Cratylus, a dialogue that is generally thought to be from Plato's early or middle period, we find reference to the essences of sensible qualities, but no indication that those essences are forms.

Let us turn to Plato's account of sensible qualities. The Timaeus provides what is undeniably Plato's clearest and most developed discussion of the nature and structure of physical things. This discussion arises within the context of a wider inquiry into the work of necessity—the principle that governs the activity of things in the physical sphere of the cosmos (the lengthy account of the work of necessity runs from 47e3–69a5). As a part of this inquiry, Plato considers the causal mechanisms that are involved in generating perceptual awareness. Here he goes through each of the sensory capacities individually, identifying the physical elements that enter into the production of the sensible qualities specific to each of them and considering how those elements interact with each other and with the soul of a perceiver to cause perceptual awareness. For the sake of brevity I will profile only three of the more illustrative examples here. Of odors, Plato says that they are caused by the affection of the vessels of the nose by vapor or mist. The elemental bodies earth, air, fire, and water are, as it happens, too large to interact with these narrow vessels and, thus, have no odor themselves (66e2–67a1). Sound is the impact of the air that comes through the ears on the brain and the blood (67b2–3). Color is a flame that emanates from bodies the parts of which are of a suitable size so as to affect the visual stream and produce visual perception (67c5–7).

One thing that we should notice about these accounts is that, in each case, the essence of the sensible quality in question—what that quality is—is specified entirely in terms of physical elements and processes. Sound is the percussion of air on the brain and the blood; color is a flame of a suitable size given off by physical bodies. That the essences of these properties can be specified in these terms is reflected not only in the accounts of the five general categories of sensible qualities—colors, sounds, tastes, scents, and textures—but also in the more specific accounts of the individual qualities that fall under these types. Thus, red, according to Plato, is a fire that dilates the visual stream to a degree intermediate between that corresponding to white and black and blends with the moisture in the eye (68b1–5).

The question is: do these accounts serve as adequate explanations of their respective qualities, such that they could qualify as fully and sufficiently specifying the essences of those qualities? If we return to the issues about explanation considered in the Phaedo, I think we will find that they do. First, recall that the explanations arrived at through natural inquiry, which had initially attracted Socrates, and which were generally limited to physical constituents and processes only, were ultimately deemed to be unsatisfactory because they contravened a certain stringent requirement of explanation—same explanans if and only if same explanandum. It was eventually determined that only an explanation in terms of essence could satisfy such a requirement. Interestingly, however, if we subject Plato's accounts of the sensible qualities, introduced above, to the demands that he puts on an adequate explanation, we find that although these accounts are given exclusively in terms of physical and/or material elements and processes, they do not contravene the requirement of explanation.

We can see this clearly if we consider an example. Take the question, ‘why does this tomato appear red?’. This question demands an explanation for why a thing is perceived to display a particular sensible quality. Based on the accounts outlined above, we might suppose that the answer that Plato would give to this question is that the tomato is physically structured so as to affect a perceiver's visual apparatus in a way consistent with causing in that perceiver a perception of red. This response, I think we can say with some confidence, does not contravene the requirement of explanation because, for Plato, these physical processes are regular and predictable. That is to say, two numerically distinct instances in which the visual stream of a perceiver is affected in the same way, assuming the perceiver's visual apparatus is functioning normally, will generate a perception of the same color. This is at least in part due to the fact that the physical world is governed by necessity. The idea that it is necessity that provides for the regularity we observe in the physical sphere of the cosmos is confirmed at Timaeus 68e6–69a5 where Plato tells us that it is because of necessity that the works of the divine cause are intelligible at all. Thus, if red is nothing other than the effect that a certain physical structure has on the visual stream, then these same physical processes will always and only be red. This, after all, is what red is; it is the essence of red or that which is designated by a true answer to the Socratic-type question: What is red? I would like to propose, therefore, that for Plato the essence of a sensible quality—what that quality is—is specified entirely in terms of (1) the physical constituents of the thing involved and (2) the process of interaction that occurs between that thing and the sensory apparatus of a perceiver.

This proposal may seem striking when considered against the backdrop of the Phaedo’s rejection of explanation in terms of material constituents in favor of explanation in terms of essence, but I do not think it need seem so. Recall that Socrates only rejects these as explanations because they contravene the requirement of explanation. Were he to find a material explanation that does not fall foul of this requirement—that is, a thing whose essence is constituted by its material constituents—he presumably would not be troubled by it.

If we look elsewhere in the Platonic corpus, we find support for the claim that there are things like this: things whose essences are not distinct from their physical constituents. In the first part of the Parmenides, which is Plato's most sustained critique of the nature of forms, Plato considers the question of the scope of forms (130b1–d9). Because of the relevance of this argument for our question, I will consider it at some length. Here Parmenides begins by asking Socrates whether he has distinguished as separate certain forms (eidê) themselves—in particular, the form of likeness, of one, and of many—and also as separate the things that participate in them (ta metechonta); Socrates replies to this that he has done so. Through the remainder of the passage Parmenides poses this same question—namely, whether or not there are separate forms—about three distinct sets of things and properties. He begins with evaluative properties, asking in particular about just, beautiful, and good. Of these Socrates says that, yes, there are separate forms. Next, Parmenides asks about certain natural kinds—human being, fire, and water; here he reminds Socrates that his question is about the existence of separate forms by specifying that the form of human being would be separate from us (chôris hemôn,130c1–2). We should note Socrates's answer here. He says that he is often puzzled (en aporia[i]) concerning these things, about whether he should (chrê) speak about them in just the way (hôsper) he did about the others or in a different way. Finally, Parmenides asks about things that, as he says, might seem absurd, like hair, clay/mud, dirt, and other undignified and base things, whether there is a form for each of these separate from what we touch with our hands. Socrates replies emphatically that there are not forms of these things (oudamôs); these things are, rather, just as we perceive them (tauta men ge haper horômen, tauta kai einai) (130d3–5).

The first point to make about this passage is that it is abundantly clear that what Parmenides is interested in is the idea that the forms are separate from the things that participate in them. In his initial question to Socrates, he uses the word separate (chôris) three times in the span of three lines in order to emphasize both that the forms are separate from their participants and that the participants are separate from the forms (130b2–4). This focus on separation suggests that what Parmenides is interested in is what we have been calling form-essences. As I argued above (section 2), it is precisely the separateness and nonphysicality in addition to the imperceptibility of form-essences that distinguishes them from other essences and makes them particularly well-suited to serve as the essences of certain properties.

With this in mind, we can turn to Socrates's response to Parmenides's question about natural kinds. Here Socrates expresses puzzlement about whether he should speak in the same way about these things as he did about the evaluative properties—that is, affirm clearly that there are separate forms corresponding to them. This uncertainty should, I think, be read as indicating not that Socrates is unsure about whether or not there are forms/essences of natural kinds, as it often is, but rather as showing that he is not at all confident that there are separate forms/essences of these things. If what Parmenides is interested in is separate forms, or what we have been calling form-essences, and if Socrates is supposed to be aware of this, then his reluctance to answer this question in the same way as he did the previous one gives us good reason to think that his unease is not about whether natural kinds have essences altogether, but rather about whether those essences are separate.

If this is correct, then Socrates's reply to Parmenides's final question—namely, whether or not there are forms of things like hair (thrixos), mud or clay (pêlos), and dirt (rhupos)—is also illuminating and deserving of comment. The question Parmenides poses here is about physical things of, as he says, a most common, everyday, and even undignified (atimotatos te kai phaulotatos) sort. Of these, Socrates says, there are no forms. Again, according to the analysis I have been pressing, we need not assume that Socrates's denial that there are forms of these kinds of things is a denial that things of this sort have essences at all; as I have argued in relation to the previous question, there is good reason to think that Socrates understands Parmenides's questions to be specifically about separate forms, or form-essences. Thus, whereas in response to the previous question Socrates expresses uncertainty about whether there are separate essences of natural kinds, here he affirms quite clearly that there are not separate essences of physical everyday things. These things are, rather, just as we see them. Furthermore, this final comment strongly suggests that Socrates thinks that coming to know what these things are involves sense perception.

It is, of course, true that immediately after this exchange (i.e., at 130e1–4), Parmenides says to Socrates that he is responding in this way because he is still young and philosophy has not yet gripped him, as he thinks it will in the future; once Socrates has been so gripped, Parmenides says, he will not consider anything to be unworthy of investigation. This response, one might contend, raises doubts about the truth of Socrates's answers to the preceding questions, and to the last question in particular. It is, however, not at all clear that Parmenides's comment here is intended to indicate that Socrates's responses are incorrect. It could, in contrast, be read as addressing Socrates's confessed tendency to flee from questions about separate forms of everyday things. According to this reading, once Socrates has reached a more advanced stage of philosophical development, he will have the confidence to defend his position about even these everyday, undignified things—namely, that they are just as we see them to be.

This idea—namely, that the essences of physical, everyday things are not separate, and the implication that if such things have essences, they can be specified entirely in terms of the physical features of those things—is also corroborated by a passage from the Theaetetus. Early in the dialogue Socrates asks Theaetetus the inquiry-launching question: What is knowledge? In response Theaetetus, like so many other interlocutors, does not give a unitary definition, but rather lists a number of different fields of knowledge. In order to illustrate to Theaetetus why such a list is inadequate as a definition of knowledge, Socrates employs the same faulty procedure on a more everyday example. He says that if he were to ask the boy what clay (pêlos) is and if Theaetetus were then to respond with a number of different kinds of clay, this would be wholly uninformative as to the nature of clay. (It is interesting to note that Plato's example of an everyday thing here is clay (pêlos), which is one of the same examples he had used in the Parmenides.) Instead, Socrates says, one should simply reply that clay is earth mixed with liquid (hoti gê hugrô[i] phuratheisa pêlos) (147c3–6). Here, again, we have an instance in which an apparently complete and adequate definition of an everyday (phaulos) physical thing is specified entirely in terms of physical constituents—earth and liquid—and a physical process—mixing. We should note at this point that it may very well be, and in fact likely is, the case that the essences of these everyday things depend, in some way, on form-essences. Thus, if clay is earth mixed with liquid, the essences of these constituents—namely, earth, liquid, and mixing—may not be specifiable solely in terms of physical constituents; specifying their essences may require that one appeal to a separate form. Unfortunately, I do not have the space to consider this issue more fully here, but I hope to do so in the future.

Having proposed this solution to the puzzle presented at the outset, I must now consider and address two potential objections. First, it might be claimed, on developmentalist grounds, that this is all for naught; for Plato's position on physical things changed from the middle dialogues, in which he conceives of the essences of physical things as precisely forms, to the late dialogues, in which he seriously questions the existence of forms and emphatically denies that there are forms corresponding to physical things. Such an objector might cite my marshaling passages from the Parmenides and Theaetetus to defend a position that is firmly rooted in the Phaedo as evidence of my vulnerability to this objection. Second, one might think that Plato never, neither in the middle nor in the late dialogues, held that physical things have essences, be they forms or otherwise. I think that both of these objections can be addressed through considering one passage from the Cratylus. I shall argue that in these lines Plato refers explicitly to the essences of both sensible qualities and physical things and that from the context of the passage we have good reason to think that this is not a reference to form-essences.

To begin with, it is striking that in the middle dialogues Plato never, or almost never, refers to forms of sensible qualities explicitly. Had he done so, we could, of course, easily answer the question of this paper in the affirmative. There is, however, one exception to this, and that is Cratylus 423e. Here Socrates says the following:

In order to understand the thrust of this comment, we must place it within its proper context. Socrates's statement here comes as part of a discussion of the imitative property of primary names. At 423b9–11 Socrates defines primary names as vocal imitations of their referents. This definition, however, is not fine-grained enough for Socrates because it fails to exclude music and animal sounds, which despite being vocal imitations do not count as names. In order to motivate the exclusion of these kinds of vocal utterances from his conception of primary names, Socrates considers the sorts of properties that music and animal sounds, on the one hand, and primary names, on the other, imitate. He begins by indicating that the things imitated by both music and animal sounds, on the one hand, and names, on the other—their referents—have sound and shape, and many of them also have color. It is, however, only these properties of things, what we might call their accidental properties, that music and animal noises can imitate through sound and that painting can imitate visually. Naming, in contrast, does not imitate these properties, but something else. This brings us to our passage in which Socrates tries to spell out what it is that names imitate. It is, as he says, the essence (ousia), as opposed to the accidents, of the thing, or indeed of the property, that the name of that thing or property imitates.

Two observations about this passage are immediately clear. First, the things that Plato is referring to here are physical things—they are things that possess accidental properties like sound, shape, and color. Second, Plato tells us that these things as well as the properties they display have essences (ousiai). These two points are, I think, not in question. If this is correct, then the second objection, outlined above is met; for the burden is now on the objector to show either that Plato is not talking about physical things or that his reference to ousia here is not a reference to essence.

The question that we must face head-on is associated with the first objection: Why should we not think that Plato's use of ousia here is a reference to forms? I think that there are two reasons—one textual and one philosophical—to think that it is not such a reference. First of all, whereas Plato had raised and discussed forms earlier in the dialogue (389bff) and had used words like eidos to indicate that it is precisely forms that are at issue here, none of these words or phrases that are typically used to refer to forms appear either in the passage we have been considering or anywhere in the immediate context. One might reasonably expect that if Plato wanted to claim here that what names imitate are forms, he would have used one of the words or phrases typical of forms to make this point, especially in view of the fact that he has discussed forms earlier in the dialogue and has done so in precisely these terms. Ademollo (Reference Ademollo2011: 276–78), for his part, argues that Plato's use of ousia in this passage is more general than his uses of it earlier in the dialogue (388c, 393d) where it referred to a simple predication. Here, he argues, ousia should be read as essence, understood as what each thing really is, or as essential feature. He finds corroboration of this reading in the immediately succeeding passage in which Plato explicates ousia as what each thing is (hekaston ho estin, 423e7–9). Similarly, Barney (Reference Barney2001: 85–86) reads Plato's use of ousia here as a reference to the nature or essence of a thing. There is, however, no indication that the essence or nature picked out by ousia is a form, understood as a separate essence.

While I concede that the above textual point is hardly decisive, it does give us some reason to think that Plato does not intend for the reader to think that the ousiai referred to here are forms. The second point is that the contrast Plato draws here is between the accidental properties of things and their essences or essential features, not between forms and things that participate in forms. What Plato says here is that (physical) things have both accidental properties and essences and that the accidental properties themselves also have essences. His point is that, in the case of both physical things and accidental properties, primary names imitate essences. For example, the word ‘tomato’ somehow imitates the essence of that red, round thing over there, and the word ‘red’ somehow imitates the essence of the color that thing displays. It seems to me that it would be simply confused to read these essences straightaway as forms, since this would obfuscate the distinction Plato is actually making. He distinguishes between those properties of a thing that a musician or a painter could possibly imitate and the essence of a thing, not between the form of a thing and that thing's physical instantiation. If this is correct, then it shows that in the Cratylus Plato is careful not to conflate essences in general with essences understood as forms. This is particularly important for our purposes, not only because this dialogue is generally considered to be early or middle, but also, and especially, because it shows that in a dialogue in which Plato raises the theory of forms he also shows sensitivity to the idea that there are essences that may not be forms.