Aquinas: On Being and Essence - Chapter 2

Chapter Two

ESSENCE AS FOUND IN COMPOSITE SUBSTANCES

[1] Form and matter are found in composite substances, as for example soul and body in man. But it cannot be said that either one of these alone is called the essence. That the matter alone of a thing is not its essence is evident, for through its essence a thing is knowable and fixed in its species and genus. But matter is not a principle of knowledge, and a thing is not placed in a genus or species through it but through that by which a thing is actual.†1 Neither can the form alone of a composite substance be called its essence, though some want to assert this.†2 It is evident from what has been said that the essence is what is signified through the definition of a thing.†3 Now the definition of natural substances includes not only form but also matter; otherwise there would be no difference between definitions in physics and in mathematics.†4 Nor can it be said that the definition of a natural substance includes matter as something added to its essence, or as something outside its essence. This is the kind of definition proper to accidents; not having a perfect essence, their definition must include their subject, which is outside their genus. It is evident, therefore, that essence embraces both matter and form.

[2] Neither can it be said that essence signifies the relation between matter and form, or something added to them, because this would necessarily be accidental or not belonging to the thing, nor could the thing be known through it, both of which are characteristics of essence. For through form, which actualizes matter, matter becomes an actual being and this particular thing. Anything that comes after that does not give matter its basic actual being, but rather a certain kind of actual being, as accidents do, whiteness for example making something actually white. When a form of this kind is acquired, we say that something comes into being not purely and simply but in a certain respect.

[3] It remains, then, that in the case of composite substances the term 'an essence' signifies the composite of matter and form. Boethius agrees with this in his commentary on the Categories, where he says that {ousia} signifies the composite;†5 for {ousia} in Greek means the same as our essentia, as Boethius himself observes.†6 Furthermore, Avicenna remarks that the quiddity of composite substances is the composition itself of form and matter.†7 The Commentator, too, says, "The nature that species have in things subject to generation is something intermediate, a composite of matter and form."†8 This is reasonable, too, for the being that a composite substance has is not the being of the form alone nor of the matter alone but of the composite, and it is essence according to which a thing is said to be.†9 So the essence, according to which a thing is called a being, cannot be either the form alone or the matter alone, but both, though form alone is in its own way the cause of this being. We observe in the case of other things composed of several principles that they do not take their name from one of these principles alone, but from both together. This is clear in tastes. Sweetness is caused by the action of the hot dissolving the moist; and although in this way heat is the cause of sweetness, a body is not called sweet from its heat but from its taste, which includes the hot and the moist.†10

[4] Because matter is the principle of individuation, it might seem to follow that an essence, which embraces in itself both matter and form, is only particular and not universal. If this were true, it would follow that universals could not be defined, granted that essence is what is signified by the definition. What we must realize is that the matter which is the principle of individuation is not just any matter, but only designated matter.†11 By designated matter I mean that which is considered under determined dimensions.†12 This kind of matter is not part of the definition of man as man, but it would enter into the definition of Socrates if Socrates could be defined. The definition of man, on the contrary, does include undesignated matter. In this definition we do not put this particular bone and this particular flesh, but bone and flesh absolutely, which are the undesignated matter of man.

[5] It is clear, therefore, that the difference between the essence of Socrates and the essence of man lies solely in what is designated and not designated. This is why the Commentator says, "Socrates is nothing else than animality and rationality, which are his quiddity."†13 The essence of the genus and the essence of the species also differ as designated and undesignated, though the mode of designation is different in the two cases. The individual is designated with respect to its species through matter determined by dimensions, whereas the species is designated with respect to the genus through the constitutive difference, which is derived from the form of the thing. This determination or designation which is in a species with regard to its genus is not caused by something existing in the essence of the species and in no way in the essence of the genus; rather, whatever is in the species is also in the genus but in an undetermined way. If indeed 'animal' were not wholly what 'man' is, but only a part of him, 'animal' could not be predicated of 'man', since no integral part may be predicated of its whole.

[6] We can see how this comes about if we examine the difference between body when it means a part of animal and body when it means a genus; for it cannot be a genus in the same way that it is an integral part. In short, the term 'body' can have several meanings.†14 In the genus of substance we give the name 'body' to that which has a nature such that three dimensions can be counted in it; but these three determined dimensions themselves are a body in the genus of quantity. It does happen that something having one perfection may also possess a further perfection, as is evident in man, who has a sensitive nature and, besides this, an intellectual nature. So, too, over and above the perfection of having a form such that three dimensions can be designated in it, another perfection can be added, such as life, or something of the kind. The term 'body', therefore, can signify that which has such a form as allows the determination of three dimensions in it, prescinding †15 from everything else, so that from that form no further perfection may follow. If anything else is added, it will be outside the meaning of body thus understood. In this way body will be an integral and material part of a living being, because the soul will be outside what is signified by the term 'body' and will be joined to this body in such a way that a living being is made up of these two, body and soul, as of two parts.

[7] The term 'body' can also be taken to mean a thing having a form such that three dimensions can be counted in it, no matter what that form may be, whether some further perfection can be derived from it or not. In this sense of the term, body is the genus of animal, because animal does not include anything that is not implicitly contained in body. The soul is not a form different from that which gives to the thing three determined dimensions. That is why, when we said that a body is that which has such a form as allows the determination of three dimensions in it, we understood this to mean any form whatsoever: animality, stoneness, or any other form. In this way the form of animal is implicitly contained in the form of body, inasmuch as body is its genus. And such also is the relation of animal to man. If 'animal' designated only a certain reality endowed with a perfection such that it could sense and be moved through an internal principle, prescinding from any other perfection, then any further perfection would be related to animal as a part and not as implicitly contained in the notion of animal, and then animal would not be a genus. But it is a genus when it signifies a thing whose form can be the source of sensation and movement, no matter what that form may be, whether it be only a sensitive soul or a soul that is both sensitive and rational.

[8] The genus, then, signifies indeterminately everything in the species and not the matter alone. Similarly, the difference designates the whole and not the form alone, and the definition also signifies the whole, as does the species too, though in a different way. The genus signifies the whole as a name designating what is material in the thing without the determination of the specific form. Thus the genus is taken from matter, though it is not matter, as we can clearly see from the fact that we call a body that which has a perfection such that it is determined by three dimensions, a perfection that is related as material with respect to a further perfection. On the contrary, the difference is a term taken from a definite form in a precise way, without including a definite matter in its primary notion; as for example when we say 'animated' (in other words, what has a soul) we do not specify what the thing is, whether it is a body or something else. That is why Avicenna says that the genus is not conceived in the difference as a part of its essence, but only as something outside its essence, as the subject is contained in the notion of its properties.†16 That is also why, according to the Philosopher,†17 a genus is not predicated of a difference properly speaking, except perhaps as a subject is predicated of its property. As for the definition or species, it embraces both, namely the determinate matter signified by the name of the genus, and the determinate form signified by the name of the difference.

[9] From this it is clear why genus, species, and difference are related proportionately to matter, form, and composite in nature, though they are not identical with them. A genus is not matter, but it is taken from matter as designating the whole; and a difference is not form, but it is taken from form as designating the whole. That is why we say that man is a rational animal, and not that he is composed of animal and rational, as we say that he is composed of soul and body. We say that man is a being composed of soul and body as from two things there is constituted a third entity which is neither one of them: man indeed is neither soul nor body. If in a sense we may say that man is composed of animal and rational, it will not be as a third reality is made up of two other realities, but as a third concept is formed from two other concepts. The concept 'animal' signifies the nature of a being without the determination of its special form, containing only what is material in it with respect to its ultimate perfection. The concept of the difference 'rational', on the other hand, contains the determination of the special form. From these two concepts is formed the concept of the species or definition. This is why, just as a reality composed of several things cannot be the subject of attribution of its constituent elements, neither can a concept be the subject of attribution of the concepts from which it is formed: we do not say that the definition is the genus or difference.

[10] Although the genus signifies the whole essence of the species, it is not necessary that different species of the same genus have one essence. The unity of the genus comes from its indetermination or indifference, but not in such a way that what is signified by the genus is a nature numerically the same in different species, to which would be added something else (the difference) determining it as a form determines a matter that is numerically one. Rather, the genus denotes a form (though not precisely any one in particular) which the difference expresses in a definite way, and which is the same as that which the genus denotes indeterminately. That is why the Commentator asserts †18 that primary matter is said to be one because of the elimination of all forms, whereas a genus is said to be one because of the community of the designated form. It is clear, therefore, that when the indetermination which caused the unity of the genus is removed by the addition of the difference, there remain species different in essence.

[11] As we have said,†19 the nature of the species is indeterminate with regard to the individual, as the nature of the genus with regard to the species. It follows that, just as the genus, when attributed to the species, implies indistinctly in its signification everything that is in the species in a determinate way, so the species, when attributed to the individual, must signify everything essentially in the individual, though in an indistinct way. For example, the term 'man' signifies the essence of the species, and therefore 'man' is predicated of Socrates. But if the nature of the species is signified with precision from designated matter, which is the principle of individuation, then it will have the role of a part. This is the way it is signified by the term 'humanity', for humanity signifies that by which man is man. Now designated matter does not make man to be man, and thus it is not in any way included among the factors that make man to be man. Since, therefore, the concept of humanity includes only that which makes man to be man, its meaning clearly excludes or prescinds from designated matter; and because the part is not predicated of the whole, humanity is predicated neither of man nor of Socrates. Avicenna concludes †20 from this that the quiddity of a composite is not the composite itself whose quiddity it is, though the quiddity itself is a composite. For example, although humanity is a composite, it is not man; in fact, it must be received in something else, namely designated matter.

[12] As was said above,†21 the species is determined relative to the genus through form, while the individual is determined relative to the species through matter. That is why it is necessary that the term signifying that from which the nature of the genus is derived, prescinding from the determinate form completing the species, signify the material part of the whole, as for example the body is the material part of man. On the contrary, the term signifying that from which the nature of the species is derived, prescinding from designated matter, signifies the formal part. For this reason 'humanity' is a term signifying a certain form, called the form of the whole.†22 Not indeed that it is something as it were added to the essential parts, form and matter, as the form of a house is added to its integral parts; but it is the form which is the whole, embracing both form and matter, but prescinding from those factors which enable matter to be designated.
[13] It is clear, then, that the essence of man is signified by the two terms 'man' and 'humanity', but in different ways, as we have said.†23 The term 'man' expresses it as a whole, because it does not prescind from the designation of matter but contains it implicitly and indistinctly, as we said the genus contains the difference.†24 That is why the term 'man' can be predicated of individuals. But the term 'humanity' signifies the essence of man as a part, because its meaning includes only what belongs to man as man, prescinding from all designation of matter. As a result it cannot be predicated of individual men. Because of this the term 'essence' is sometimes attributed to a thing and sometimes denied of it: we can say 'Socrates is an essence' and also 'the essence of Socrates is not Socrates'.