1038bSince the subject of our inquiry is substance, let us return to it. Just as the substrate and the essence and the combination of these are called substance, so too is the universal. With two of these we have already dealt, i.e. with the essence¹ and the substrate²; of the latter we have said that it underlies in two senses—either being an individual thing (as the animal underlies its attributes), or as matter underlies the actuality. The universal also is thought by some³ to be in the truest sense a cause and a principle. Let us therefore proceed to discuss this question too; for it seems impossible that any universal term can be substance. First, the substance of an individual is the substance which is peculiar to it and belongs to nothing else; whereas the universal is common; for by universal we mean that which by nature appertains to several things. Of what particular, then, will the universal be the substance? Either of all or of none. But it cannot be the substance of all; while, if it is to be the substance of one, the rest also will be that one; because things whose substance is one have also one essence and are themselves one. Again, substance means that which is not predicated of a subject, whereas the universal is always predicated of some subject. But perhaps although the universal cannot be substance in the sense that essence is, it can be present in the essence, as “animal” can be present in “man” and “horse.” Then clearly there is in some sense a formula of the universal. It makes no difference even if there is not a formula of everything that is in the substance; for the universal will be none the less the substance of something; e.g., “man” will be the substance of the man in whom it is present. Thus the same thing will happen again⁴; e.g. “animal” will be the substance of that in which it is present as peculiar to it. Again, it is impossible and absurd that the individual or substance, if it is composed of anything, should be composed not of substances nor of the individual, but of a quality; for then non-substance or quality will be prior to substance or the individual. Which is impossible; for neither in formula nor in time nor in generation can the affections of substance be prior to the substance, since then they would be separable. Again, a substance will be present in “Socrates,” who is a substance; so that it will be the substance of two things. And in general it follows that if “man” and all terms used in this way are substance, none of the elements in the formula is the substance of anything, nor can it exist apart from the species or in anything else; I mean, e.g., that neither “animal” nor any other element of the formula can exist apart from the particular species. If we look at the question from this standpoint it is obvious that no universal attribute is substance; and it is also clear from the fact that none of the common predicates means “so-and-so,” 1039abut “such and-such.” Otherwise amongst many other awkward consequences we have the “third man.” ⁵ Again, it is clear in this way too. Substance can not consist of substances actually present in it; for that which is actually two can never be actually one, whereas if it is potentially two it can be one. E.g., the double consists of two halves—that is, potentially; for the actualization separates the halves. Thus if substance is one, it cannot consist of substances present in it even in this sense, as Democritus rightly observes; he says that it is impossible for two to come from one, or one from two, because he identifies substance with the atoms.⁶ Clearly then the same will also hold good in the case of number (assuming that number is a composition of units, as it is said to be by some); because either 2 is not 1, or there is not actually a unit in it. The consequence involves a difficulty; for if no substance can consist of universals, because they mean “of such a kind,” and not a particular thing; and if no substance can be actually composed of substances, every substance will be incomposite, and so there will be no formula of any substance. But in point of fact it is universally held, and has been previously stated,⁷ that substance is the only or chief subject of definition; but on this showing there is no definition even of substance. Then there can be no definition of anything; or rather in a sense there can, and in a sense cannot. What this means will be clearer from what follows later.⁸

From these same considerations it is clear also what consequence follows for those who maintain that the Forms are substances and separable, and who at the same time make the species consist of the genus and the differentiae. If there are Forms, and if “animal” is present in the man and the horse, it is either numerically one and the same with them, or not. (In formula they are clearly one; for in each case the speaker will enunciate the same formula.) If, then, there is in some sense an Absolute Man, who is an individual and exists separately, then the constituents, e.g. “animal” and “two-footed,” must have an individual meaning and be separable and substances. Hence there must be an Absolute Animal too. (i) Then if the “animal” which is in the horse and the man is one and the same, as you are one and the same with yourself, 1039bhow can the one which in things that exist separately be one, and why should not this “animal” also be separated from itself? Again, if it is to partake of “two-footed” and of “many-footed,” an impossibility follows; for contrary attributes will belong to it although it is one and individual. But if it does not, in what sense is it that one calls an animal “two-footed” or “terrestrial”? Perhaps the terms are “combined” and “in contact” or “mixed.” But all these expressions are absurd. (2) “But there is a different “animal” in each species.” Then there will be practically an infinity of things of which “animal” is the substance, since it is not in an accidental sense that “man” is derived from “animal.” Again, the Absolute Animal will be a plurality. For (a) the “animal” in each species will be the substance of that species, since the species is called after it and no other thing. Otherwise “man” would be derived from that other thing, which would be the genus of “man.” (b) Further, all the constituents of “man” will be Ideas. Then, since nothing can be the Idea of one thing and the substance of another (for this is impossible), each and every “animal” in the various species will be the Absolute Animal. Further, from what will these Forms be derived, and how can they be derived from the Absolute Animal? Or how can “the animal,” whose very essence is “animal,” exist apart from the Absolute Animal? And further, in the case of sensible things both these and still more absurd consequences follow. If, then, these consequences are impossible, clearly there are not Forms of sensible things in the sense in which some hold that there are.

Since substance is of two kinds, the concrete thing and the formula (I mean that one kind of substance is the formula in combination with the matter, and the other is the formula in its full sense), substances in the former sense admit of destruction, for they also admit of generation. But the formula does not admit of destruction in the sense that it is ever being destroyed, since neither does it so admit of generation (for the essence of house is not generated, but only the essence of this house); formulae are , and are not, independently of generation and destruction; for it has been shown⁹ that no one either generates or creates them. For this reason also there is no definition or demonstration of particular sensible substances, because they contain matter whose nature is such that it can both exist and not exist. Hence all the individual instances of them are perishable. If, then, the demonstration and definition of necessary truths requires scientific knowledge, and if, just as knowledge cannot be sometimes knowledge and sometimes ignorance (it is opinion that is of this nature), so too demonstration and definition cannot vary (it is opinion that is concerned with that which can be otherwise than it is)— 1040athen clearly there can be neither definition nor demonstration of individual sensible substances. For (a) things which perish are obscure to those who have knowledge of them when they are removed from the sphere of their perception, and (b) even though their formulae are preserved in the soul, there will no longer be either definition or demonstration of them. Therefore in cases relating to definition, when we are trying to define any individual, we must not fail to realize that our definition may always be upset; because it is impossible to define these things. Nor, indeed, can any Idea be defined; for the Idea is an individual, as they say, and separable; and the formula must consist of words, and the man who is defining must not coin a word, because it would not be comprehensible. But the words which are in use are common to all the things which they denote; and so they must necessarily apply to something else as well. E.g., if a man were to define you, he would say that you are an animal which is lean or white or has some other attribute, which will apply to something else as well. And if it should be said that there is no reason why all the attributes separately should not belong to several things, and yet in combination belong to this alone, we must reply, (1.) that they also belong to both the elements; e.g., “two-footed animal” belongs both to “animal” and to “two-footed” (and in the case of eternal elements this is even necessarily so; since they are prior to the compound, and parts of it. Indeed they are also separable, if the term “man” is separable—for either neither can be separable, or both are so. If neither, the genus will not exist apart from the species, or if it is so to exist, so will the differentia); (2.) that “animal” and “two-footed” are prior in being to “two-footed animal,” and that which is prior to something else is not destroyed together with it. Again, if the Ideas are composed of Ideas (for constituents are less composite than that which they compose), still the elements of which the Idea is composed (e.g. “animal” and “two-footed”) will have to be predicated of many particulars. Otherwise, how can they be known? For there would be an Idea which cannot be predicated of more than one thing. But this is not considered possible; every Idea is thought to admit of participation. Thus, as we have said,¹⁰ the impossibility of defining individuals is hard to realize when we are dealing with eternal entities, especially in the case of such as are unique, e.g. the sun and moon. For people go wrong not only by including in the definition attributes on whose removal it will still be sun—e.g., “that which goes round the earth,” or “night-hidden” (for they suppose that if it stops or becomes visible¹¹ it will no longer be sun; but it is absurd that this should be so, since “the sun” denotes a definite substance)—they also mention attributes which may apply to something else; e.g., if another thing with those attributes comes into being, clearly it will be a sun. The formula, then, is general; 1040bbut the sun was supposed to be an individual, like Cleon or Socrates. Why does not one of the exponents of the Ideas produce a definition of them? If they were to try, it would become obvious that what we have just said is true.