The question naturally presents itself, what sort of parts belong to the form and what sort belong not to it but to the concrete object. Yet if this is not plain it is impossible to define the particular; because the definition refers to the universal and the form. Therefore if it is not clear what kind of parts are material and what kind are not, the formula of the thing will not be clear either. In the case of things which can be seen to be induced in specifically different materials, as, e.g., a circle is in bronze and stone and wood, it seems clear that these things, the bronze and the stone, are in no sense part of the essential substance of the circle, because it is separable from them. As for things which are not visibly separable, there is no reason why the same should not apply to them; e.g., if all the circles that had ever been seen were bronze; 1036bfor the bronze would be none the less no part of the form, but it is difficult to separate it in thought. For example, the form of “man” is always manifested in flesh and bones and elements of this kind; then are these actually parts of the form and formula, or are they not so, but matter, though since the form is not induced in other materials, we cannot separate it? Now since this seems to be possible, but it is not clear when, some thinkers¹ are doubtful even in the case of the circle and the triangle, considering that it is not proper to define them by lines and continuous space, but that all these are to the circle or triangle as flesh or bone is to man, and bronze or stone to the statue; and they reduce everything to numbers, and say that the formula of “line” is the formula of 2. And of the exponents of the Forms, some make 2 the Ideal line, and some the form of the line²; for they say that in some cases the form and that of which it is the form, e.g. 2 and the form of 2, are the same; but in the case of “line” this is no longer so. It follows, then, that there is one form of many things whose form is clearly different (a consequence which confronted the Pythagoreans too³), and that it is possible to make one supreme Form of everything, and not to regard the rest as forms. In this way, however, all things would be one. Now we have stated that the question of definitions involves some difficulty, and have shown why this is so. Hence to reduce everything in this way and to dispose of the matter is going too far; for some things are presumably a particular form in particular matter, or particular things in a particular state. And the analogy in the case of the living thing which the younger Socrates⁴ used to state is not a good one; for it leads one away from the truth, and makes one suppose that it is possible for a man to exist without his parts, as a circle does without the bronze. But the case is not similar; for the animal is sensible and cannot be defined without motion, and hence not unless its parts are in some definite condition; for it is not the hand in any condition that is a part of a man, but only when it can perform its function, and so has life in it. Without life in it it is not a part. And with respect to mathematical objects, why are the formulae of the parts not parts of the formulae of the whole; e.g., why are the formulae of the semicircles not parts of the formula of the circle? for they are not sensible. Probably this makes no difference; because there will be matter even of some things which are not sensible. 1037aIndeed there will be matter in some sense in everything which is not essence or form considered independently, but a particular thing. Thus the semicircles will be parts not of the universal circle but of the particular circles, as we said before⁵—for some matter is sensible, and some intelligible. It is clear also that the soul is the primary substance, and the body matter; and “man” or “animal” is the combination of both taken universally. And “ Socrates” or “Coriscus” has a double sense, that is if the soul too can be called Socrates (for by Socrates some mean the soul and some the concrete person); but if Socrates means simply this soul and this body, the individual is composed similarly to the universal. Whether there is some other material component of these substances besides their matter, and whether we should look for some further substance in them, such as numbers or something of that kind, must be considered later.⁶ It is with a view to this that we are trying to determine the nature of sensible substances, since in a sense the study of sensible substances belongs to physics or secondary philosophy; for the physicist must know not only about the matter, but also about the substance according to the formula; this is even more essential. And in the case of definitions, in what sense the elements in the formula are parts of the definition, and why the definition is one formula (for the thing is clearly one, but in virtue of what is it one, seeing that it has parts?); this must be considered later.⁷ We have stated, then, in a general account which covers all cases, what essence is, and how it is independent; and why the formula of the essence of some things contains the parts of the thing defined, while that of others does not; and we have shown that the material parts of a thing cannot be present in the formula of the substance (since they are not even parts of the substance in that sense, but of the concrete substance; and of this in one sense there is a formula, and in another sense there is not. There is no formula involving the matter, for this is indeterminate; but there is a formula in accordance with the primary substance, e.g., in the case of a man, the formula of the soul; because the substance is the indwelling form, of which and of the matter the so called concrete substance is composed. E.g., concavity is such a form, since from this and “nose” is derived “snub nose” and “snubness”—for “nose” will be present twice over in these expressions); but in the concrete substance, e.g. snub nose or Callias, matter will be present too.⁸ We have stated also that the essence and the individual are in some cases the same, 1037bas in the case of the primary substances; e.g. crookedness and “essence of crookedness,” if this is primary. By primary I mean that which does not imply the presence of something in something else as a material substrate. But such things as are material or are compounded with matter are not the same as their essence; not even if they are accidentally one, e.g. Socrates and “cultured”; for these are only accidentally the same.

Now let us first deal with definition, in so far as it has not been dealt with in the Analytics; for the problem stated there⁹ has a bearing upon our discussion of substance. The problem I mean is this: what constitutes the unity of the thing of which we say that the formula is a definition? E.g., in the case of man, “two-footed animal”; for let us take this as the formula of “man.” Why, then, is this a unity and not a plurality, “animal” and “two-footed”? For in the case of “man” and “white” we have a plurality when the latter does not refer to the former, but a unity when it does refer to it, and the subject, “man,” has an attribute; for then they become a unity and we have “the white man.” But in the case before us one term does not partake of the other; the genus is not considered to partake of its differentiae, for then the same thing would be partaking simultaneously of contraries, since the differentiae by which the genus is distinguished are contrary. And even if it does partake of them, the same argument applies, since the differentiae are many; e.g. terrestrial, two-footed, wingless. Why is it that these are a unity and not a plurality? Not because they are present in one genus, for in that case all the differentiae of the genus will form a unity. But all the elements in the definition must form a unity, because the definition is a kind of formula which is one and defines substance, so that it must be a formula of one particular thing; because the substance denotes one thing and an individual, as we say. We must first¹⁰ examine definitions which are reached by the process of division. For there is nothing else in the definition but the primary genus and the differentiae; the other genera consist of the primary genus together with the differentiae which are taken with it. E.g., the primary genus is “animal”; the next below it, “two-footed animal”; and again, “two-footed wingless animal”; and similarly also if the expression contains more terms still. 1038aIn general it does not matter whether it contains many or few terms, nor, therefore, whether it contains few or two. Of the two one is differentia and the other genus; e.g., in “two-footed animal” “animal” is genus, and the other term differentia. If, then, the genus absolutely does not exist apart from the species which it includes, or if it exists, but only as matter (for speech is genus and matter, and the differentiae make the species, i.e. the letters, out of it), obviously the definition is the formula composed of the differentiae. But further we must also divide by the differentia of the differentia. E.g., “having feet” is a differentia of “animal”; then in turn we must discover the differentia of “animal having feet” qua “having feet.” Accordingly we should not say that of “that which has feet” one kind is winged and another wingless, (that is if we are to speak correctly; if we say this it will be through incapability), but only that one kind is cloven-footed and another not; because these are differentiae of “foot,” since cloven-footedness is a kind of footedness. And thus we tend always to progress until we come to the species which contain no differentiae. At this point there will be just as many species of foot as there are differentiae, and the kinds of animals having feet will be equal in number to the differentiae. Then, if this is so, obviously the ultimate differentia will be the substance and definition of the thing, since we need not state the same things more than once in definitions, because this is superfluous. However, it does happen; for when we say “footed two-footed animal” we have simply said “animal having feet, having two feet.” And if we divide this by its proper division, we shall be stating the same thing several times, as many times as there are differentiae. If, then, we keep on taking a differentia of a differentia, one of them, the last, will be the form and the substance. But if we proceed with reference to accidental qualities—e.g. if we divide “that which has feet” into white and black—there will be as many differentiae as there are divisions. It is therefore obvious that the definition is the formula derived from the differentiae, and strictly speaking from the last of them. This will be clear if we change the order of such definitions, e.g. that of man, saying “two-footed footed animal”; for “footed” is superfluous when we have already said “two-footed.” But there is no question of order in the substance; for how are we to think of one part as posterior and the other prior? With regard, then, to definitions by division, let this suffice as a preliminary statement of their nature.