Chapter 2 — On the essences of composite substances

In composite substances we find form and matter, as in man there are soul and body. We cannot say, however, that either of these alone is the essence of the thing. That matter alone is not the essence of the thing is clear, for it is through its essence that a thing is knowable and is placed in a species or genus. But matter is not a principle of cognition; nor is anything determined to a genus or species according to its matter but rather according to what it is in act. Nor is form alone the essence of a composite thing, however much certain people may try to assert this. From what has been said, it is clear that the essence is that which is signified by the definition of the thing. The definition of a natural substance, however, contains not only form but also matter; otherwise, the definitions of natural things and mathematical ones would not differ. Nor can it be said that matter is placed in the definition of a natural substance as something added to the essence or as some being beyond the essence of the thing, for that type of definition is more proper to accidents, which do not have a perfect essence and which include in their definitions a subject beyond their own genus. Therefore, the essence of a composite substance clearly comprises both matter and form.

Nor can it be said that essence signifies the relation between the matter and the form or something superadded to these, for then the essence would of necessity be an accident and extraneous to the thing, and the thing would not be known through its essence, all of which are proper to an essence. Through the form, surely, which is the act of the matter, the matter is made a being in act and a certain kind of thing. Thus, something that supervenes does not give to the matter existence in act simply, but rather existence in act in a certain way, just as accidents do, as when whiteness makes something actually white. Hence, when such a form is acquired, we do not say that the thing is generated simply but only in a certain way.

It remains, therefore, that the term ‘essence,’ used with respect to composite substances, signifies that which is composed of matter and form. This conclusion is consistent with what Boethius says in his commentary on the Categories, namely, that ousia signifies what is composite; ousia, of course, is for the Greeks what essence is for us, as Boethius himself says in his book de Persona et duabus naturis. (Although quoted by various thirteenth century authors, this statement does not appear in the text of de Persona et duabus naturis as we have it.) Avicenna even says (Metaphysics 5.5) that the quiddity of a composite substance is the very composition of the form and the matter. And commenting on Book 7 of Aristotle’s Metaphysics, the Commentator says: The nature that species in generable things have is something in the middle; that is, it is composed of matter and form (Metaphysics 7, com. 27).

Moreover, reason supports this view, for the existence of a composite substance is neither form alone nor matter alone but is rather composed of these. The essence is that according to which the thing is said to exist; hence, it is right that the essence by which a thing is denominated a being is neither form alone not matter alone but both, although existence of this kind is caused by the form and not by the matter. Similarly, we see that in other things that are constituted from many principles, the thing is not denominated from just one or the other of the principles but rather from that which embraces both. Thus, with respect to flavors, sweetness is caused by the action of a warm animal body digesting what is wet, and although in this way warmth is the cause of the sweetness, nevertheless a body is not called sweet by reason of the warmth, but rather by reason of the flavor, which embraces both the warmth and the wetness.

But because matter is the principle of individuation, it would perhaps seem to follow that essence, which embraces in itself simultaneously both form and matter, is merely particular and not universal. From this it would follow that universals have no definitions, assuming that essence is what is signified by the definition. Thus, we must point out that the principle of individuation is not matter understood in just any way, but only signate matter is the principle of individuation. I call ‘signate matter’ matter considered under determinate dimensions. Such matter is not included in the definition of man as man, but it would be included in the definition of Socrates, if Socrates had a definition. In the definition of man, however, is included non-signate matter: in the definition of man we do not include ‘this bone’ and ‘this flesh’ but only bone and flesh absolutely, which are the non-signate matter of man.

Hence, the essence of man and the essence of Socrates do not differ except as the signate differs from the non-signate, and so the Commentator says, in Metaphysics 7, com. 20: Socrates is nothing other than animality and rationality, which are his quiddity. Similarly, the essence of a genus and the essence of a species differ as signate from non-signate, although in the case of genus and species a different mode of designation is used with respect to each. For the designation of the individual with respect to the species is through matter determined by dimensions, while the designation of the species with respect to the genus is through the constitutive difference, which is taken from the form of the thing. This determination or designation, however, which is made in the species with respect to the genus, is not through something that exists in the essence of the species but in no way exists in the essence of the genus. On the contrary, whatever is in the species is also in the genus as undetermined. If animal were not all that man is but rather only a part of him, then animal would not be predicated of man, for no integral part may be predicated of its whole.

We can see how this happens by considering how body taken as a part of animal differs from body taken as the genus of animal, for body cannot be a genus in the way it is an integral part. The term ‘body’ can thus be accepted in several ways. Body is said to be in the genus of substance in that it has a nature such that three dimensions can be designated in it. These three designated dimensions are the body that is in the genus of quantity. Now, it sometimes happens that what has one perfection may attain to a further perfection as well, as is clear in man, who has a sensitive nature and, further, an intellective one. Similarly, above this perfection of having a form such that three dimensions can be designated in it, there can be joined another perfection, as life or some similar thing. This term ‘body’ therefore can signify a certain thing that has a form such that from the form there follows in the thing designatability in three dimensions exclusively: namely, such that from this form no further perfection follows, but if some other thing is superadded, it is beyond the signification of body thus understood. And understood in this way, body will be an integral and material part of animal, because in this way soul will be beyond what is signified by the term ‘body,’ and it will supervene on body such that from these two (namely, soul and body), animal is constituted as from parts.

This term ‘body’ can also be understood as signifying a certain thing that has a form such that three dimensions can be designated in it, whatever form this may be, such that either from the form some further perfection can arise or not. Understood in this way, body will be the genus of animal, for there will be understood in animal nothing that is not implicitly contained in body. Now, the soul is not a form other than that through which there can be designated in the thing three dimensions, and therefore, when we say that body is what has a form from which three dimensions can be designated in the body, we understand that there is some kind of form of this type, whether soul, or rockness, or any other form. And thus the form of animal is implicitly contained in the form of body, when body is its genus.

Such too is the relation of animal to man. For if ‘animal’ named just a certain thing that has a perfection such that it can sense and move by a principle existing in itself, excluding any other perfection, then whatever further perfection may supervene would be related to animal as another part thereof, and not as implicitly contained in the notion of animal, and in this way animal would not be a genus. But animal is a genus when it signifies a certain thing from the form of which sensation and motion can arise, whatever this form may be, whether a sensible soul only or a soul both sensible and rational.

Therefore, the genus signifies indeterminately the whole of what is in the species and not the matter only. Similarly, the difference also signifies the whole and not the form only. So, too, the definition signifies the whole, as does the species. But although these all signify the same thing, they do so in different ways. For the genus signifies the whole as a certain denomination determining that which is material in the thing without a determination of its proper form, whence the genus is taken from the matter, although it is not the matter. This is clear from the fact that we call something a body in that the thing has a perfection such that in it three dimensions can be designated, and this perfection is related materially to some further perfection. Conversely, the difference is like a certain denomination taken from the determined form, beyond the first conception by which the matter is determined. So, when we speak of something animated (that is, something that has a soul), this does not determine what the thing is, whether it is a body or something else. Hence, Avicenna says (Metaphysics 5.6) that the genus is not understood in the difference as a part of its essence but only as a being beyond its essence, even as a subject is with respect to the concept of a passion. And thus the genus is not predicated of the difference in itself, as the Philosopher says in Metaphysics 3.8 (Aristotle, Metaphysics, 998b24.) and in Topics 4.2, (Aristotle, Topics, 122b22–26.) unless perhaps as a subject is predicated of a passion. But the definition or the species comprehends both: namely, the determined matter that the term ‘genus’ designates and the determined form that the term ‘difference’ designates.

From this is it clear why the genus, the difference, and the species are related proportionally to the matter, the form, and the composite in nature, although they are not the same as these things. For the genus is not the matter, although it is taken from the matter as signifying the whole; nor is the difference the form, although it is taken from the form as signifying the whole. We thus say that man is a rational animal, but not that he is composed of animal and rational in the sense that we say that man is composed of soul and body: man is said to be composed of soul and body as from two things from which a third thing is constituted different from each of the two, for man is neither body nor soul. But if man is said in some sense to be composed of animal and rational, it will not be as a third thing composed from these two things, but as a third concept composed from these two concepts. The concept of animal is without determination of a special form and expresses the nature of the thing from that which is material with respect to its ultimate perfection; the concept of the difference, rational, consists in the determination of a special form. From these two concepts are constituted the concept of the species or the definition. Thus, just as a thing constituted from other things does not have predicated of it these other things, so too a concept does not have predicated of it the concepts of which it is constituted: clearly, we do not say that the definition is either the genus or the difference.

Although the genus may signify the whole essence of the species, nevertheless the various species of which it is the genus do not have the same essence, for the unity of the genus proceeds from its very indetermination or undifferentiation. Nor is it the case that what is signified through the genus in the various species is numerically one nature such that to it there supervenes some other thing, which is the difference that determines it, as a form determines matter that is numerically one. Rather, the genus signifies some form (though not determinately this one or that one), which the difference expresses determinately, the very one that is signified indeterminately through the genus. And thus the Commentator says in Metaphysics 12, (Aquinas knew this book as Book XI.) com. 14, that prime matter is called ‘one’ by the removal of all forms, but the genus is called ‘one’ through the commonality of forms signified. Hence, once the indetermination (which was the cause of the unity of the genus) is removed through the addition of the difference, the various species remain diverse by essence.

Furthermore, since, as was said above, 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, and since, further, the genus, as predicated of the species, includes in its signification (although indistinctly) everything that is in the species determinately, so too does the species, as predicated of the individual, signify everything that is in the individual essentially, although it signifies this indistinctly. In this way, the essence of the species is signified by the term ‘man,’ and so man is predicated of Socrates. If, however, the nature of the species is signified in such a way as to exclude designate matter, which is the principle of individuation, then the species is related to the individual as a part; and this is how the term ‘humanity’ signifies, for humanity signifies that by which a man is a man. Designate matter, however, is not that by which a man is a man, and it is in no way contained among those things that make a man a man. Since, therefore, the concept of humanity includes only those things by which a man is a man, designate matter is excluded or omitted, and since a part is not predicated of its whole, humanity is predicated neither of man nor of Socrates. Thus, Avicenna says (Metaphysics 5.5) that the quiddity of a composite thing is not the composite thing of which it is the quiddity, even though the quiddity itself is composite, just as humanity, while composite, is not man. On the contrary, it must be received in something that is designate matter.

But since, as was said above, the designation of the species with respect to the genus is through form, and the designation of the individual with respect to the species is through matter, the term signifying that from which the nature of the genus is taken, when it excludes the determinate form that completes the species, signifies the material part of the whole: for example, as body is the material part of man. However, the term signifying that from which the nature of the species is taken, when it excludes designate matter, signifies the formal part. Thus, humanity is signified as a certain form, and it is said that it is the form of the whole: not, certainly, as a form superadded to the essential parts (the form and the matter) as the form of a house is superadded to its integral parts. Rather, humanity is the form that is the whole, embracing both form and matter, although excluding those things through which matter can be designated.

Therefore, the term ‘man’ and the term ‘humanity’ both signify the essence of man, though in diverse ways, as was said above. The term ‘man’ signifies the essence as a whole: in other words, insofar as the essence does not exclude designation of matter but implicitly and indistinctly contains it, in the way in which we said that the genus contains the difference. Hence, the term ‘man’ is predicated of individuals. But the term ‘humanity’ signifies the essence of man as a part because it contains in its signification only what belongs to man insofar as he is man, and excludes all designation. Thus, it is not predicated of individual men. And for this reason the term ‘essence’ is sometimes found predicated of the thing, as when we say that Socrates is a certain essence; and sometimes the term ‘essence’ is denied of the thing, as when we say that the essence of Socrates is not Socrates.