Chapter 3 — How essence is related to genus, species, and difference

Having seen what the term ‘essence’ signifies in composite substances, we ought next to see how essence is related to the logical intentions of genus, species, and difference. Since that to which the intentions of genus or species or difference is appropriate is predicated of this signate singular, it is impossible that a universal intention, like that of the species or genus, should be appropriate to the essence if the genus or species is signified as a part, as in the term ‘humanity’ or ‘animality.’ Thus, Avicenna says (Metaphysics 5.6) that rationality is not the difference but the principle of the difference. For the same reason, humanity is not a species, and animality is not a genus. Similarly, we cannot say that the intention of species or genus is appropriate to the essence as to a certain thing existing beyond singulars, as the Platonists used to suppose, for then the species and the genus would not be predicated of an individual: we surely cannot say that Socrates is something that is separated from him, nor would that separate thing advance our knowledge of this singular thing. And so it remains that the intention of genus or species is appropriate to the essence as the essence is signified as a whole, as the term ‘man’ or ‘animal’ implicitly and indistinctly contains the whole of what is in the individual.

The nature, however, or the essence thus understood can be considered in two ways. First, we can consider it according to its proper notion, and this is to consider it absolutely. In this way, nothing is true of the essence except what pertains to it absolutely: thus everything else that may be attributed to it will be attributed falsely. For example, to man, in that by which he is man, pertains animal and rational and the other things that fall in his definition; white or black or whatever else of this kind that is not in the notion of humanity does not pertain to man in that by which he is a man. Hence, if it is asked whether this nature, considered in this way, can be said to be one or many, we should concede neither alternative, for both are beyond the concept of humanity, and either may befall the conception of man. If plurality were in the concept of this nature, it could never be one, but nevertheless it is one as it exists in Socrates. Similarly, if unity were in the notion of this nature, then it would be one and the same in Socrates and Plato, and it could not be made many in many individuals. Second, we can also consider the existence the essence has in this thing or in that: in this way something can be predicated of the essence accidentally by reason of what the essence is in, as when we say that man is white because Socrates is white, although this does not pertain to man in that by which he is man.

The nature considered in this way, however, has a double existence. On the one hand, it exists in singulars, and, on the other hand, it exists in the soul, and from each of these the nature acquires certain accidents. In singulars, furthermore, the essence has a multiple existence according to the multiplicity of singulars. Nevertheless, if we consider the essence in the first, or absolute, sense, none of these pertain to the essence. For it is false to say that the essence of man, considered absolutely, has existence in this singular, because if existence in this singular pertained to man insofar as he is man, man would never exist outside this singular. Similarly, if it pertained to man insofar as he is man not to exist in this singular, then the essence would never exist in the singular. But it is true to say that man, but not insofar as he is man, has whatever may be in this singular or in that one, or else in the soul. Therefore, the nature of man considered absolutely abstracts from every existence, though it does not exclude the existence of anything either. And the nature thus considered is the one predicated of each individual.

Nevertheless, the nature understood in this way is not a universal notion, because unity and commonality belong to the notion of a universal, but to human nature, considered absolutely, neither of these belong. For if commonality were in the concept of man, then in whatever humanity were found, there would be found commonality, and this is false, because no commonality is found in Socrates, but rather whatever is in him is individuated. Similarly, the notion of genus or species does not pertain to human nature because of the existence that that nature has in individuals, for human nature is not found in individuals with a unity that it will be one thing in all the individuals, which the notion of a universal demands. It remains, therefore, that the notion of species pertains to human nature according to the existence human nature has in the intellect.

Human nature in the intellect has existence abstracted from everything that individuates, and thus it is related uniformly to all individuals that exist outside the soul, as it is equally a likeness of all of them, and it leads to knowledge of all of them insofar as they are men. Since the nature in the intellect has this relation to each individual, the intellect invents the notion of species and attributes it to the nature. Hence, the Commentator, in de Anima 1, com. 8, says that the intellect is what makes universality in things; and Avicenna says the same in his Metaphysics 5.2. Although this nature understood in the intellect has the notion of a universal in relation to things outside the soul (because it is one likeness of them all), as the nature has existence in this intellect or in that one, it is a certain particular understood species. The Commentator, therefore, is in error in de Anima 3, com. 5, when he wants to infer the unity of intellect in all men from the universality of the understood form, because the universality of the form does not arise from the existence the form has in the intellect but rather from its relation to things as a likeness of them. It is as if there were a corporeal statue representing many men; that image or species of statue would have a singular and proper existence insofar as it exists in this matter, but it would have the character of commonality insofar as it was a common representative of many men.

Since human nature, considered absolutely, is properly predicated of Socrates, and since the notion of species does not pertain to human nature considered absolutely but only accidentally because of the existence the nature has in the intellect, the term ‘species’ is not predicated of Socrates, for we do not say that Socrates is a species. We would have to say that Socrates is a species if the notion of species pertained to man arising from the existence that the nature has in Socrates or from the nature considered absolutely, that is, insofar as man is man. For whatever pertains to man insofar as he is man is predicated of Socrates.

But ‘to be predicated’ pertains to a genus in itself, because being predicated is placed in its definition. Now, predication is completed by the action of the intellect in compounding and dividing, and it has as its basis the unity in the real thing itself of those things one of which is said of another. Hence, the notion of predicability can be placed under the notion of this intention which is the genus, which is itself completed by an act of the intellect. Still, that to which the intellect attributes the intention of predicability by compounding it with another is not itself this intention of genus; it is rather that to which the intellect attributes the intention of genus, as, for instance, to what is signified by the term ‘animal.’

We have thus made clear how the essence or nature is related to the notion of species, for the notion of species is not among those that pertain to the essence considered absolutely; nor is it among the accidents that follow from the existence that the essence has outside the soul, as whiteness or blackness. Rather, the notion of species is among the accidents that follow from the existence the essence has in the intellect. And in this way as well do the notions of genus or difference pertain to essences.