Aquinas: On Being and Essence - Chapter 3

Chapter Three

THE RELATION OF ESSENCE TO GENUS, SPECIES, AND DIFFERENCE

[1] Having seen what the term 'an essence' means in composite substances, we must examine how it is related to the notion †1 of genus, species, and difference. That to which the notion of genus, species, or difference belongs is attributed to an individual, determinate thing. It is therefore impossible that the notion of universal (that is to say, of genus or species) should belong to an essence when it is expressed as a part, for example by the term 'humanity' or 'animality'. That is why Avicenna says †2 that 'rationality' is not a difference, but the principle of a difference; and for the same reason 'humanity' is not a species nor 'animality' a genus. Nor can we say that the notions of genus and species belong to an essence as a reality existing outside individual things, as the Platonists held,†3 because then the genus and species would not be attributed to the individual: we cannot say that Socrates is something separated from himself. This separated entity, moreover, would be of no help in knowing the individual. We conclude, therefore, that the notion of genus or species applies to an essence when it is expressed as a whole, for example by the term 'man' or 'animal', containing implicitly and indistinctly everything in the individual.

[2] Understood in this sense, a nature or essence can be considered in two ways.†4 First, absolutely, according to its proper meaning. In this sense nothing is true of it except what belong to it as such; whatever else may be attributed to it, the attribution is false. For example, to man as man belong 'rational', 'animal', and everything else included in his definition; but 'white' or 'black', or any similar attribute not included in the notion of humanity, does not belong to man as man. If someone should ask, then, whether a nature understood in this way can be called one or many, we should reply that it is neither, because both are outside the concept of humanity, and it can happen to be both. If plurality belonged to its concept, it could never be one, though it is one when present in Socrates. So, too, if oneness belonged to its concept, the nature of Socrates and of Plato would be identical, and it could not be multiplied in many individuals.

[3] In a second way a nature or essence can be considered according to the being it has in this or that individual. In this way something is attributed to it accidentally, because of the subject in which it exists, as we say that man is white because Socrates is white, though this does not belong to man insofar as he is man.

[4] This nature has a twofold being: one in individual things and the other in the soul, and accidents follow upon the nature because of both beings. In individuals, moreover, the nature has a multiple being corresponding to the diversity of individuals; but none of these beings belongs to the nature from the first point of view, that is to say, when it is considered absolutely. It is false to say that the essence of man as such has being in this individual: if it belonged to man as man to be in this individual it would never exist outside the individual. On the other hand, if it belonged to man as man not to exist in this individual, human nature would never exist in it. It is true to say, however, that it does not belong to man as man to exist in this or that individual, or in the soul. So it is clear that the nature of man, considered absolutely, abstracts from every being, but in such a way that is prescinds from no one of them; and it is the nature considered in this way that we attribute to all individuals.

[5] Nevertheless, it cannot be said that a nature thus considered has the character of a universal,†5 because unity and community are included in the definition of a universal, neither of which belongs to human nature considered absolutely. If community were included in the concept of man, community would be found in everything in which humanity is found. This is false, because there is nothing common in Socrates; everything in him is individuated.†6 Neither can it be said that human nature happens to have the character of a genus or species through the being it has in individuals, because human nature is not found in individual men as a unity, as though it were one essence belonging to all of them, which is required for the notion of a universal.

[6] It remains, then, that human nature happens to have the character of a species only through the being it has in the intellect. Human nature has being in the intellect abstracted from all individuating factors, and thus it has a uniform character with regard to all individual men outside the soul, being equally the likeness of all and leading to a knowledge of all insofar as they are men. Because it has this relation to all individual men, the intellect discovers the notion of species and attributes it to the nature. This is why the Commentator says that it is the intellect that causes universality in things.†7 Avicenna makes the same point.†8

[7] Although this nature apprehended by the intellect has the character of a universal from its relation to things outside the soul, because it is one likeness of them all, nevertheless as it has being in this or that intellect it is a particular apprehended likeness. The Commentator was clearly in error then; he wanted to conclude that the intellect is one in all men from the universality of the apprehended form.†9 In fact, the universality of this form is not due to the being it has in the intellect but to its relation to things as their likeness. In the same way, if there were a material statue representing many men, the image or likeness of the statue would have its own individual being as it existed in this determinate matter, but it would have the nature of something common as the general representation of many men.

[8] Because it is human nature absolutely considered that is predicated of Socrates, this nature does not have the character of a species when considered absolutely; this is one of the accidents that accompany it because of the being it has in the intellect. That is why the term 'species' is not predicated of Socrates, as though we were to say 'Socrates is a species'. This would necessarily happen, however, if the notion of species belonged to man in his individual being in Socrates, or according to his absolute consideration, namely insofar as he is man; for we predicate of Socrates everything that belongs to man as man. Nevertheless, it is essential to a genus to be predicated: this is included in its definition. Predication is something achieved by the intellect in its act of combining and dividing, having for its foundation in reality the unity of those things, one of which is attributed to the other.†10 That is why the notion of predicability can be included in the meaning of the notion of genus, a notion that is also produced by an act of the intellect. But that to which the intellect attributes the notion of predicability, combining it with something else, is not the concept itself of genus, but rather that to which the intellect attributes the concept of genus, as for example what is signified by the term 'animal'.

[9] From this we can see how essence or nature is related to the notion of species. The notion of species is not one of those items that belong to the nature when it is considered absolutely, nor is it one of the accidents that follow upon the nature because of the being it has outside the soul, like whiteness or blackness. Rather, the notion of species is one of the accidents that follow upon the nature because of the being it has in the intellect; and it is in this way, too, that the notions of genus and difference belong to it.