21 On Species
matter of a thing, because there are genera which are common to simple objects lacking any composition of matter and form. Color, for example, is common to colors, but colors are not composed ofmatter and form. Thus, when the philosophical authorities say that the genus is a part of a thing or that it is the matter ofa thing or something of the like, they ought to be glossed to read that the genus is said to be a part of a thing or the material element ofa thing because it is, so to speak, the material element in the definition or the description of the thing. In natural things the matter is presupposed by the form and the form comes to it. Similarly if something is to be defined, one first posits the genus; the essential or accidental differences are added afterwards. Thus, the genus is a part of the definition, and it is first in definition in the way in which matter is first in the composite thing. For this (and for no other) reason writers say that the genus is the matter and a part of a thing.
One might want to say that the genus is a part of the definition; but since the definition is really the same as the thing defined, the genus is a part of the thing defined. The response is that, properly speaking, it is false to say that the definition is really the same as the thing defined. What is true is that the definition and the definitum signify the same thing and that is all that the authors mean here.
It should be noted also that the genus is predicated of both species and particulars. And here we must be aware that things are different as we focus on the loose and strict senses of'genus'. In the strict sense every genus requires distinct and dissimilar things for which the terms of which it is predicated supposit. But when we take the term 'genus' in a broad sense this is not so. Indeed, it is sufficient that the things of which the intention genus is predicated and which supposit for other things merely be common notions which exclude each other. Thus, if it were the case that the only substantial entities were men, the intentions multitude and number could, in this loose sense, be construed as genera. For many and multitude could be predicated of the common notions two, three, four, etc., none of which is predicated of the others. But many authoritative texts are not to be construed as using the notion of a genus in this loose sense.
21: On Species Philosophers define the notion of a species in a similar way. They say that a species is something predicated in quid of many things which differ numerically.
On Species First it ought to be noted that like genera species are intentions of the soul.
Consequently they do not belong to the essence ofindividuals, although they are predicable of individuals.
The difference between a species and its genus is not the kind of difference which separates a whole from its parts; for properly speaking, the genus is not a part of the species, nor is the species a part of the genus. They differ rather in that the species is common to fewer items than its genus so that the genus is the sign of more things and the species of fewer. Thus, the name animal signifies more things than the name man, for the former signifies all the animals; whereas, the latter signifies only men. This point holds true of genera and Species generally. It is in this sense that the species is the subjective part of a genus; it signifies fewer things. Thus, even the word 'man' can be said to be a part of the word 'animal', that is, 'man' signifies fewer things than 'animal'. This is the correct way to use the term 'subjective part'.
The genus when predicated of the species does not stand for itself but for the things which it signifies. Similarly, the species when predicated of many individuals stands not for itself but for the individuals in question. The species is not many; it is predicated of many. Neither is the species really in the particular, for then it would be a part of the individual. But this is impossible, for the species is neither matter nor form; and, further, there are individuals which do not have parts. Consequently, the species cannot be part of an individual. It is on the contrary a sign of the particular; it signifies all the particulars subsumed under it.
But it should be noted that of the intentions which are genera and species, some are highest level genera, others are subalternate genera and species, and still others are lowest level species.
A highest level genus is a genus which does not have any genera above it; that is, a highest level genus is something which when taken universally does not have some other genus predicable of both itself and some other genus.
However, according to one view, it is possible to predicate some other genus of a highest level genus. Thus, some say that this is true: substance is a quantity, but since they deny that 'Every substance is a quantity' is true, they can consistently hold that substance is a highest level genus. They could also say that a highest genus is that of which, universally taken, no other genus is predicated in quid. Thus although they would agree that substance is a quanlity, they would deny that quantity is predicated in quid of substance universally taken.
But the lowest level species is an intention not having a species under it; that is. a lowest level species is not predicated in quid of any common notion, although it may be predicated in quid of many particulars. Those universals that fall between the highest level genera and the lowest level species are called subalternate genera and species.
22: On the Comparison of Species and Genus Now that we have seen what genera and species are we ought to compare these intentions to bring out their common and peculiar features.
They differ in that while the genus is predicated of the species, the species is not predicated of the genus. This should not be understood to mean that the species is in no way predicated of the genus. That would be wrong; for since the genus is predicated of the species, the species is in turn predicated of the genus. From 'Man is an animal', for example, we can derive by conversion,
'An animal is a man'. If the genus is predicated of the species, it follows necessarily that the species is predicated of the genus. This point should be understood along the following lines: when a genus actually contains under it different individuals from different species, the genus is truly predicated of the species taken universally; but the species is not predicated of the genus taken universally, although it is truly predicated of the genus when the genus is taken particularly. Thus, it is true that every man is an animal, but it is false that every animal is a man.
Suppose, however, that there were no animals except man. In addition to the truth of both the indefinite proposition 'An animal is a man' and the particular proposition 'Some animal is a man', the universal proposition "Every animal is a man' would also be true (as well as 'Every man is an animal'). Thus, the species can be predicated of the genus taken not only particularly but universally, but this possibility does not exist in the case where the genus incorporates specifically different particulars.
It should be noted that although the genus is predicated of the species, such predication is not always necessary. Thus, the following proposition is not necessary: 'Man is an animal', for if there were no men the proposition would be false. In the same way 'Some composite of body and intellective soul is an animal' would be false because of the false implication. Although it is contingent that man is an animal, the conditional proposition 'If a man is, then an animal is' is necessary.
Another difference is that the genus contains the species but the species does not contain the genus. This should be understood to mean that while the genus is capable of being predicated of more things—that is what 'contains means here—than the species, the species cannot be predicated of more things than its genus.
Also, a genus is naturally prior to its species. This should not be understood to mean that the intention which is a genus is by nature prior to the intention which is its species. For it can surely happen that the intention which is a On the Comparison of Species and Genus species can be in the soul without the intention which is its genus; the reverse can also happen. Thus, when someone forms the Proposition 'Socrates is a man', it is not necessary that he have in his mind all of the intentions which are genera vis-a-vis Socrates. When they have said that the genus is by nature prior to its
Species, writers have only meant that the genus is more general than its species.
Thus, although existence is predicated ofagenus, it does not necessarily follow that it is predicated of all the species under the genus. It is possible that existence be truly denied of some species when it is truly predicated of the relevant genus. The reverse, however, is not possible. And this is only to say that inferences like the following are valid: aman is; therefore, an animal is and a stone is; therefore, a substance is. The reverse of these inferences however are not valid.
A further point of divergence is that if the relevant genera are destroyed, the species are also destroyed. This should not be understood in the sense of 'real destruction' so that if the genus is corrupted it is necessary that its species also be corrupted, but not conversely, for that is simply false. For even if the generic intention animal, which is predicable of both men and donkeys, were to cease to exist in my soul (thus to be corrupted), it is not necessary that the intention man, which is its species, also cease to exist in my soul. The aforesaid point should be understood in terms oflogical destruction. Thus, an inference moving from the negation of a genus to the negation of a species is valid.
The following, for example, is valid: Animal is not; therefore, man is not.
The converse, however, is not a valid inference. Similarly, it follows that if A is not an animal, A is not a man; the reverse, however, does not follow. Likewise, from 'No animal runs', we can infer that no man runs but not the reverse.
There are many other points of difference Separating genera and species.
Since | have spoken of these elsewhere and since an understanding of them can be derived from what I have said here and from what I shall say further on, I shall not pursue the matter.
Genera and species agree in that both are predicable of many. Theology confirms this point, for although there is just one sun, divine power could produce many. Likewise, even if there is just one angel of a given species, God could, if He wished, produce many angels of one and the same species. This is true in spite of the fact that the Philosopher would deny it.
Genera and species also agree in that both are prior to that of which they are predicated. This should not be understood to mean that a genus is naturally prior to its species and the species in turn to its particulars. That is false, for a particular can exist even if there are no souls; whereas, species and genera require a soul for their existence. They are said to be prior in that while the inference from an individual to its species and genus is valid, the reverse form of inference is not valid.