CHAPTER Two:
ST. THOMAS AQUINAS
intellect in any mode whatsoever; for a thing is not intelligible except by virtue of its definition and essence. And thus also the Philosopher in the Fourth book of his Metaphysics says that every substance is a nature. But the name nature taken in this sense is seen to signify the essence of a thing inasmuch as it has a disposition towards an operation proper to the thing, since no thing is lacking in its proper operation. Indeed the name quiddity is taken from that which signifies the definition; but it is called essence according as by virtue of it and in it being has existence.
But because being is asserted absolutely and primarily of substances and secondarily and as if in a certain respect of accidents, hence it is that essence also exists truly and properly in substances, but exists in accidents in a certain mode and in a certain respect. Some substances indeed are simple and others are composite, and in both there is an essence.
But essence is possessed by simple substances in a truer and more noble mode according as simple substances have a more exalted existence, for they are the cause of those which are composite,—at least the primary substance, which is God, is. But since the essences of these substances are more concealed from us, therefore we must begin from the essences of composite substances in order that instruction may be made more suitably from what is easier.
CHAPTER Two:
In composite substances, therefore, matter and form are noted, as for instance in man soul and body are noted.
Moreover it cannot be said that either of these alone is called essence. For it is evident that matter alone is not the essence of the thing, because it is by means of its essence that the thing is both known and ordered in its species and genus. But matter is not the principle of cognition, nor is anything determined as regards genus and species according to it (matter), but according to that by means of which something is in act. And furthermore neither can form alone be called the essence of composite substance, however much some attempt to assert this. From what has been said it is clear that essence is what is signi-
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OF BELIEF
THE AGE fied by the definition of the thing. But the definition of - natural substances contains not only form but also matter; for otherwise natural definitions and mathematical definitions would not differ. Nor can it be said that matter is posited in the definition of a natural substance as an addition to its essence or as a being outside of its essence, since this mode of definition is more proper to accidents which do not have a perfect essence; whence it follows that they must admit the subject into their definition, which (subject) is outside of their genus. It is clear, therefore, that essence comprehends matter and form. But it cannot be said that essence signifies a relation which is between matter and form, or that it is something superadded to them, since something superadded would of necessity be accidental or extraneous to the thing, nor could the thing be conceived by means of it, for everything is appropriate to its essence. For by the form, which is the actuality of matter, matter is made being in act and a this somewhat.
Whence that which is superadded does not give existence in act simply to matter, but existence in act of such sort as likewise accidents make, as for instance whiteness makes something white in act. Wherefore whenever such form is acquired it is not said to be generated simply but in a certain respect.
. Whence it follows that the essence by virtue of which a thing is called being is not form alone, nor matter alone, but both; although in its mode the form is the cause of its existence. We discover it indeed thus in other things which are constituted from more than one principle, since a thing is not named from one of those principles alone, but from that which unites both...
But because the principle of individuation is matter, it perhaps seems to follow from this that essence which unites in itself both matter and form would be only particular and not universal. From this it would follow that universals do not have definition, if essence is what is signified by means of the definition. One should therefore understand that matter in any mode whatsoever is not taken to be the principle of individuation, but only signated matter.
. Accordingly, it is clear that the essence of Socrates and the essence of man do not differ except according to signate
é and non-signate. Whence the Commentator remarks upon the seventh of the Metaphysics: "Socrates is nothing other than animality and rationality which are his quiddity." Thus also the essence of genus and of species differ according to signate and non-signate, although there is a different mode of designation for each of them, because the designation of the individual with respect to species is by means of matter determined by dimensions, whereas the designation of species in respect to genus is by means of the constitutive difference which is taken from the form of the thing.>.
And ..
. the nature of species is indeterminate in respect to the individual, just as the nature of genus is indeterminate with respect to species, hence it is that, just as that which is genus according as it is predicated concerning species implies in its signification, although indistinctly, all that is determinate in species, thus likewise it follows that what is species, according as it is predicated of the individual, signifies all that which is in the individual essentially although indistinctly. And in this mode the essence of Socrates is signified by the name of man, and as a consequence man is predicated of Socrates. But if the nature of the species be signified with the exclusion of designated matter, which is the principle of individuation, it will thus be disposed as a part (by means of the partitive mode).
And in this mode it is signified by the name humanity, for humanity signifies that in virtue of which man is man. But designated matter is not that in virtue of which man is man; and, therefore, in no mode is it contained among those things from which man possesses manness. Since therefore humanity includes in its concept only those things from which man possesses manness, it is clear that designated matter is excluded from or cut off from its signification.
And since the part is not predicated of the whole, hence it is that humanity is not predicated either of man or of Socrates.
. Since, as has been said, the designation of species in respect to genus is by virtue of form, whereas the designation of the individual in respect to species is by virtue of matter, it follows therefore that the name signifying that whence the nature of genus is taken, with the ex-
THE AGE OF BELIEF
clusion of the determinate form perfecting the species, should signify the material part of the whole itself, as the body is the material part of man. But the name signifying that whence the nature of species is taken, with the exclusion of designated matter, signifies the formal part. And therefore humanity is signified as a certain form, and is spoken of as that which is the form of the whole; not indeed as if it were superadded to the essential parts, namely, to form and matter, as for instance the form of a house is superadded to its integral parts; but rather it is form that is the whole, that is, embracing form and matter, yet with the exclusion of those things by means of which matter is found to be designated. So, therefore, it is clear that the name man and the name humanity signify the essence of man, but in different modes, as has been said, since the name man signifies it as a whole, inasmuch as it does not exclude the designation of matter but contains it implicitly and indistinctly, as for instance it has been said that the genus contains the difference. And therefore the name man is predicated of individuals. But the name humanity signifies the essence as a part, since it does not contain in its signification anything except what is of man inasmuch as he is man, and because it excludes all designation of matter; whence it is not predicated of individual man. And for this reason likewise the name essence sometimes is found predicated of a thing, for Socrates is said to be an essence, and sometimes it is denied, as for instance it is said that the essence of Socrates is not Socrates.
CHAPTER THREE:
Having seen, therefore, what is signified by the name of essence in composite substances, we should see in what mode it is disposed towards the ratio of genus, species, and difference.
. The ratio of species applies to human nature according to that existence which it has in the intellect. For human nature itself has an existence in the intellect abstracted from all individuations, and therefore it has a uniform ratio to all individuals which are outside the soul, according as it is equally the likeness of all and