Politis’ monograph is a welcome contribution to the current conversation concerning Plato’s Forms. Its principal aim is arguing that Forms are essences—not things that have essences—and are essences “in the sense of that which is designated by an adequate and true answer to the ti esti question [What is it?]” (1). It is a secondary aim to show that Plato attributes certain characteristics to Forms because this notion of essence—what Politis sometimes describes as the “original and minimal notion of essence” (1)—requires them. Such characteristics include being “changeless, uniform, not perceptible by the senses, knowable only by reasoning, the basis of causation and explanation, distinct from sense-perceptible things, necessary for thought and speech, [and] separate from physical things” (1). That this latter aim is the secondary aim is important for Politis. He notes that in most of the current scholarship, the focus is on the characteristics themselves, with Forms’ being essences mentioned only as an afterthought (5). But, according to the author, this gets things the wrong way around; that Forms are essences comes first, then the principal characteristics.
Central to Politis’ argument is the Hippias Major, where Socrates puts to Hippias the question, “What is beauty?” (286d). Hippias maintains that the question is “something trivial and worth practically nothing” (Hp. Ma. 286e5-6), since examples and exemplars of beauty are readily available—a beautiful girl, horse, or lyre, for instance. Socrates proceeds to show Hippias that he is mistaken. It is a consequence of their discussion that it is not possible to perceive by the senses what beauty—and, Politis argues, many other qualities too—is. What beauty is is something imperceptible and grasped in some other way. (See Chapters 1 and 2.) From this foundation, Politis then shows how, through careful examination of passages from Phaedo, Republic, Parmenides, Timaeus, and Philebus, many of the characteristics said of Plato’s Forms are requirements for something’s being a satisfactory answer to the ti esti question. It is not the case, though, that all characteristics of Forms are connected to the ti esti question in this direct way. The claim that Forms are the basis of causation and explanation is not so connected, although it is still connected to Forms’ being essences. (See Chapter 6.) This also seems to be the case for the necessity of Forms for judgments about sense-perceptible and physical things. (See Chapter 7.)
So much for an overview of the monograph’s main argument. I now offer two comments. The first concerns the second part of the Parmenides. The second concerns the thorny issue of self-predication.
Chapter 3 concerns the simplicity and changelessness of Forms. That is, that each Form is one (hen), in the sense of being unitary, uniform (monoeides), and non-composite (asuntheta), as well as changeless (see Phd. 78c10-d7, 79a2 and Sph. 249b5, 249b12-c1, for various ways of expressing this) and eternal (aidion) or immortal (athanaton). The chapter also engages with the question: Are Forms logically independent of each other?
There is a case to be made that the answer is Yes, at least prior to the Sophist, where we read of the “interweaving of Forms” (sumplokē eidōn), and perhaps some sections of the second part of the Parmenides (see, for instance, 160b-163b). For how else, someone may inquire, can we understand the lesson of the first section of argument of the second part of the Parmenides (137c-142a)? This section starts from the hypothesis, “If it [the One] is one,” and ends with the conclusions that the One has no name and there is no account, knowledge, perception, or opinion of it, all because the One in no way partakes (metechei) of being (141e). It seems, someone may argue, that Forms were originally considered logically independent of each other, that this is mistaken, and that this section of argument shows why.
Yet there is also a case to be made that the answer is No, that prior to the Sophist and, perhaps, some sections of the second part of the Parmenides, Forms were not considered logically independent of each other. Politis quotes the following sentence from Republic V:
Each of them [i.e., ‘all the Forms’] is itself one, but because they manifest themselves (phantazomena) everywhere in communion with actions, bodies, and one another, each of them appears to be (phainesthai) many. (476a5-8; trans. Grube-Reeve, adapted by Politis)
It is difficult to read this sentence in a way that does not suggest that already in the Republic Forms were logically dependent on each other.
As support for Politis’ position, I offer something Socrates says when presenting the Simile of the Sun (R. VI.507a-509b). Here Socrates describes the Good as the cause of knowledge and truth, and he remarks that knowledge and truth are beautiful things. Then he says that “the Good is other (allo) and more beautiful (kallion) than they” (R. 508e4-5). I assume that “other” and “more beautiful” here are straightforward predications—Socrates says of the Good that it has the qualities of otherness (that is, difference) and beauty—and not predications about the structure of the nature of the Good or Pauline predications (and they are certainly not self-predications). If this is correct, then here too is textual evidence that Forms were not considered logically independent of each other prior to the Sophist and, perhaps, some sections of the second part of the Parmenides.
Still, the question remains: What is the lesson of the first section of argument in the second part of the Parmenides if not that which was outlined above? Politis argues that its closing moves explain an earlier claim made by Parmenides, that “Forms, and the defining of Forms, are necessary for thought” (179; see Prm. 135b7-c7). This explanation is accomplished by specifying two general conditions for thought. First, “thought is of something that is” (190). Second, “thought requires complexity in the object of thought; and such complexity requires at least two things standing in relation to each other, namely, the relation ‘X belongs to Y’” (191). This is a welcome answer to the above question, as it accommodates the inclination to read the first section of argument as delivering a lesson about the need for Forms to be “predicationally many,” while at the same time avoiding tension with those passages from the Republic that strongly suggest that Forms were not (and perhaps were never) conceived of as logically independent from each other. As Politis writes, the second part of the Parmenides is “as much about thinking as it is about being” (179), as much about thought as it is about predication.
Politis closes the monograph with some comments on the thorny issue of self-predication, which he understands as the issue of whether “Plato [ever] thought that the Form of the quality of F is itself F and F in the same way that other things are F” (231, original emphasis). Politis’ answer is No, and for two reasons. First, Plato is not committed to the so-called “transmission theory of causation,” which says that “causation works by the cause transmitting its character to the effect, and hence that the cause must be like the effect” (112-113). (See Chapter 6.) Second, the general argument that Forms are essences shows that their principal characteristics are such as they are because they are required for “an adequate and true answer to the ti esti question” (231), and so it is not the case that “the Form of the quality F is itself F and F in the same way as other things are F” (231, original emphasis).
The defender of self-predication (which this reviewer is) can respond to Politis in the following way. First, while commitment to the transmission theory of causation requires a commitment to self-predication, a commitment to self-predication does not require a commitment to the transmission theory of causation. So, if defenders of self-predication reject the view that Plato was ever committed to the transmission theory of causation (as this reviewer does), they can still maintain that Plato was committed to self-predication.
Second, and more importantly, there is a question concerning just what it means to deny the claim, and especially the italicized part, that “the Form of the quality F is itself F and in the same way that other things are F” (231, original emphasis). It could mean denying that the Form of the quality F has or instantiates the quality F, just as other things have or instantiate the quality F. For example, that the Form of the Beautiful instantiates the quality of beauty just as Matisse’s The Dessert instantiates the quality of beauty, though each manifests this quality in different ways. If this is what is meant, I find it difficult to deny that some Forms are self-predicative in this way, namely, the Great Kinds that are the focus of the central sections of the Sophist (254b-257b). Being has the quality of being, just as my cat Wilbur does; Identity instantiates the quality of self-identity, just as the succulent on my coffee table does; Difference is different (from everything save itself), just as I am. If, however, denying the above claim amounts to denying that the explanation for the Form of the quality F’s being itself F is the same as the explanation for other things’ being F, then this is a plausible position concerning self-predication. Elsewhere I have argued that the explanation for the Form of the quality F’s instantiating F need not be different from the explanation for other things’ being F. My view is that the “explanation for instantiation is always participation, whether the object participated in is something else or the thing itself,” which means that the explanation for the Form of the quality F’s instantiating F is self-participation. Yet there is also a case to be made that it is the Form of the quality F’s being the what it is to be F that explains its instantiating the quality F. If the latter is in fact Plato’s view, then it would be correct to deny that Plato was committed to self-predication, as Politis understands it, because the explanation for the F’s instantiating F is different from the explanation for other things’ instantiating F. But which explanation is in fact Plato’s explanation remains, for the moment, an open question.
Despite this point of disagreement, the monograph’s principal argument is quite compelling and the monograph itself is likely to be of most interest, and most accessible, to scholars with an interest in Plato’s metaphysics and ontology—Chapters 6 and 7 are especially dense—or philosophers with a general interest in theories of essence in ancient philosophy.
 All references, unless I indicate otherwise, are to Politis’ monograph.
 For statements of the form “the F is X,” where such statements say something about the structure of the nature of the F, see, for instance, Constance Meinwald, Plato’s Parmenides (New York: Oxford University Press, 1991) and Constance Meinwald, “Good-bye to the Third Man,” in The Cambridge Companion to Plato, ed. Richard Kraut (New York: Cambridge University Press, 1992), 365-396. For Pauline predications, see, for instance, S. Peterson, “A Reasonable Self-Predication Premise for the Third Man Argument,” The Philosophical Review 82, no. 4 (October 1973): 451-470 and Gregory Vlastos, “An Ambiguity in the Sophist,” in Platonic Studies, ed. Gregory Vlastos (Princeton: Princeton University Press, 1973), 270-322.
 I adopt the phrase “predicationally many” from Patricia Curd. It means that Forms have many predicates, both in the sense that they are many things and in the sense that they are not many things. See Patricia Curd, “Parmenides 131c-132b: Unity and Participation,” History of Philosophy Quarterly 3, no. 2 (April 1986): 125-136.
 The principal evidence in support of Plato’s commitment to the transmission theory of causation is an argument that begins at Phaedo 95e.
 See Michael J. Augustin, “Self-Instantiation and Self-Participation,” Plato Journal 22 (October 2021): 11-17.
 Augustin, “Self-Instantiation and Self-Participation,” 16.