De ente et essentia

In composite substances, therefore, form and matter are known, as in man, soul and body. But it cannot be said that either of these alone is called the essence. For it is clear that matter alone is not the essence of a thing, since a thing is both knowable through its essence and ordered in a species or genus; but matter is neither the principle of knowledge nor determined by it to a genus or species, but according to what a thing is in act. Nor can form alone be called the essence of a composite substance, although some try to assert this. For from what has been said it is clear that essence is what is signified by the definition of a thing; but the definition of natural substances contains not form alone but matter as well, otherwise natural and mathematical definitions would not differ.

Nor can it be said that matter is placed in the definition of a natural substance as something added to its essence, or as a being outside its essence, because this mode of definition belongs properly to accidents, which do not have a complete essence; hence in their definition they must receive a subject that lies outside their genus. It is therefore clear that essence comprehends both matter and form.

Nor can essence signify the relation between matter and form, or something superadded to them, because this would necessarily be an accident and extraneous to the thing, and a thing would not be known through it; whereas all these belong to essence. For through form, which is the act of matter, matter becomes a being in act and this particular thing. Hence what supervenes does not give matter being in act simply, but being in act of such-and-such a kind, just as accidents do: whiteness makes something actually white. Therefore, when such a form is acquired, a thing is not said to be generated simply, but in a qualified sense.

It remains, then, that in composite substances the name essence signifies what is composed of matter and form. This agrees with Boethius's statement in his commentary on the Categories, where he says that ousia signifies the composite; for among the Greeks ousia means the same as essence among us, as he himself says in On the Two Natures. Avicenna likewise says that the quiddity of composite substances is the very composition of form and matter. The Commentator also says, on Book VII of the Metaphysics: “The nature that species have in generable things is something intermediate, namely, composed of matter and form.” Reason agrees with this, since the being of a composite substance belongs neither to form alone nor to matter alone, but to the composite itself; and essence is that according to which a thing is said to be. Hence the essence by which a thing is denominated a being must be neither form alone nor matter alone, but both, although in its own way form alone is the cause of this being.

For in other things too that are constituted from several principles, we see that a thing is not denominated from only one of those principles, but from what embraces both. This is clear in flavors: sweetness is caused by the action of heat digesting moisture; and although heat is in this way the cause of sweetness, a body is not called sweet by its heat, but by its flavor, which embraces the hot and the moist.

But since matter is the principle of individuation, it might seem to follow that essence, which embraces matter and form together, is only particular and not universal. It would then follow that universals have no definition, if essence is what is signified by definition. We must therefore know that matter is not the principle of individuation in every way in which it is taken, but only designated matter; and I call designated matter that which is considered under determinate dimensions. This matter is not placed in the definition of man insofar as he is man, but it would be placed in the definition of Socrates, if Socrates had a definition.

In the definition of man, however, undesignated matter is placed: the definition does not contain this bone and this flesh, but bone and flesh absolutely, which are the undesignated matter of man.

Thus it is clear that the essence of man and the essence of Socrates differ only according to the designated and the undesignated. Hence the Commentator says on Book VII of the Metaphysics: “Socrates is nothing other than animality and rationality, which are his quiddity.”

The essence of genus and species likewise differ according to the designated and the undesignated, although the mode of designation is different in the two cases. The designation of an individual with respect to a species is through matter determined by dimensions; the designation of a species with respect to a genus is through the constitutive difference taken from the form of the thing. But this determination or designation of the species with respect to the genus is not through something existing in the essence of the species that is in no way in the essence of the genus. Rather, whatever is in the species is also in the genus, though not determined. For if animal were not the whole of what man is but a part of him, it would not be predicated of him, since no integral part is predicated of its whole.

How this occurs can be seen by considering how body differs insofar as it is posited as a part of animal and insofar as it is posited as a genus; for it cannot be a genus in the same way as it is an integral part. The name body, therefore, can be taken in several ways. Body, insofar as it is in the genus of substance, is said from having a nature such that three dimensions can be designated in it; the three designated dimensions themselves are the body that is in the genus of quantity.

In things it happens that what has one perfection reaches a further perfection as well, as is clear in man, who has a sensitive nature and, beyond it, an intellectual nature. Likewise, upon the perfection of having such a form that three dimensions can be designated in it, another perfection may be added, such as life or something of the kind. The name body can therefore signify a thing having a form from which the designability of three dimensions follows, with a restriction: namely, that no further perfection follows from that form, and if anything else is added, it lies outside the signification of body so understood. In this way body is the integral and material part of animal, because soul lies outside what is signified by the name body and supervenes upon body, so that animal is constituted from the two, soul and body, as from its parts.

The name body can also be taken to signify a thing having a form from which three dimensions can be designated in it, whatever that form may be, whether a further perfection can proceed from it or not. In this way body is the genus of animal, because in animal there is nothing to be taken that is not implicitly contained in body. Soul is not another form than that through which three dimensions could be designated in that thing. Thus, when body was said to be what has such a form that three dimensions can be designated in it, any form whatever was understood, whether soul, stoniness, or anything else. In this way the form of animal is implicitly contained in the form of body, insofar as body is its genus.

Animal also bears this relation to man. If animal signified only a thing having a perfection such that it could sense and move through a principle existing in it, with the restriction of another perfection, then every further perfection would be related to animal as a co-part, and not as implicitly contained in the notion of animal; thus animal would not be a genus. But it is a genus insofar as it signifies a thing from whose form sensation and movement can proceed, whatever that form may be, whether it is merely a sensitive soul or a sensitive and rational soul together.

Thus genus signifies indeterminately the whole that is in the species; it does not signify matter alone. Difference likewise signifies the whole, not form alone; and definition, and species, also signify the whole. They do so in different ways. Genus signifies the whole as a denomination determining what is material in the thing without determining its proper form; hence genus is taken from matter, although it is not matter. Body is an example, since it is said from having such a perfection that three dimensions can be designated in it, and this perfection stands materially in relation to a further perfection.

Difference, conversely, is a denomination taken from a determinate form, except that determinate matter is not included in its first understanding. Thus “animate” means that which has a soul, without determining what it is, whether body or something else. Avicenna therefore says that genus is not understood in difference as a part of its essence, but only as a being outside its essence, just as a subject is included in the understanding of passions. Hence genus, strictly speaking, is not predicated of difference, as the Philosopher says in Book III of the Metaphysics and Book IV of the Topics, unless perhaps as a subject is predicated of a passion. Definition or species, however, comprehends both: the determinate matter designated by the name genus and the determinate form designated by the name difference.

From this the reason is clear why genus, species, and difference correspond proportionally to matter, form, and composite in nature, although they are not identical with them. Genus is not matter, but is taken from matter while signifying the whole; nor is difference form, but is taken from form while signifying the whole. Thus we say that man is rational animal, not that he is made from animal and rational as we say that he is made from soul and body. From soul and body man is said to be made as a third thing constituted from two things, which he is neither of: man is neither soul nor body. But if man is in some way said to be made from animal and rational, this is not as a third thing from two things, but as a third understanding from two understandings. The understanding of animal is without determination of a specific form, expressing the nature of a thing according to what is material in relation to the ultimate perfection; the understanding of rational consists in determination of a specific form. From these two understandings is constituted the understanding of the species or definition. Therefore, just as a thing constituted from certain things does not receive their predication, so neither does an understanding receive the predication of the understandings from which it is constituted: we do not say that a definition is genus or difference.

Although genus signifies the whole essence of a species, it does not follow that the essence of different species having the same genus is one essence, because the unity of genus proceeds from its indetermination or indifference. It is not that what is signified by genus is one numerically identical nature in different species, with another thing, the difference, supervening to determine it, as form determines matter, which is one in number. Rather, genus signifies a form—not this or that determinate form—which the difference expresses; and the form expressed by the difference is not other than the form signified indeterminately by the genus. Hence the Commentator says in Book XI of the Metaphysics that prime matter is called one by removal of all forms, whereas genus is called one by the community of the form signified. It is therefore clear that, when the indetermination that caused the unity of genus is removed by addition of the difference, species remain essentially diverse.

And because, as has been said, the nature of the species is indeterminate with respect to the individual just as the nature of the genus is with respect to the species, it follows that, just as genus, when predicated of the species, implicitly signified in its meaning, though indistinctly, the whole that is determinate in the species, so what is species, when predicated of an individual, must signify the whole that is essential in the individual, though indistinctly. In this way the essence of the species is signified by the name man, and man is predicated of Socrates.

But if the nature of the species is signified with restriction from designated matter, which is the principle of individuation, it has the character of a part. In this way it is signified by the name humanity, for humanity signifies that by which man is man. Designated matter is not that by which man is man, and therefore is in no way contained among the things from which man has his being man. Since humanity in its understanding includes only those things from which man has his being man, designated matter is excluded or cut off from its signification. And because a part is not predicated of the whole, humanity is predicated neither of man nor of Socrates. Hence Avicenna says that the quiddity of a composite is not the composite itself whose quiddity it is, although the quiddity itself is composite; thus humanity, although composite, is not man. Rather, it must be received in something that is designated matter.

But since, as has been said, the designation of a species with respect to a genus is through form, while the designation of an individual with respect to a species is through matter, it is therefore necessary that a name signifying that from which the nature of the genus is taken, with the restriction of the determinate form perfecting the species, signify the material part of the whole, just as body is the material part of man; whereas a name signifying that from which the nature of the species is taken, with the restriction of designated matter, signifies the formal part. Therefore humanity is signified as a certain form and is called the form of the whole—not as though superadded to the essential parts, namely form and matter, as the form of a house is superadded to its integral parts, but rather as the form that is the whole, comprehending form and matter, though with the restriction of the principles through which matter is apt to be designated.

It is therefore clear that the name man and the name humanity signify the essence of man, but in different ways. The name man signifies it as a whole, since it does not cut off the designation of matter but implicitly and indistinctly contains it, just as genus was said to contain difference; hence the name man is predicated of individuals. The name humanity signifies it as a part, because its signification contains only what belongs to man insofar as he is man and cuts off every designation; hence it is not predicated of individual men. For this reason the name essence is sometimes found predicated of a thing: we say that Socrates is a certain essence; and sometimes it is denied, as when we say that the essence of Socrates is not Socrates.