The habitual relativity is predicated of that which has been brought into relation with its correlative by something in which both originally communicated, but which, owing to the destruction of one of the two, has ceased to be common. This relativity in Latin is properly called habitudo—that is, “habitual connotation”; and the subject thus related is spoken of as habens se ad aliquid—a phrase which we do not attempt to translate, and which is used by philosophers in a more general sense to express all kinds of relations.[87] Thus a murderer is still habitually related to the man whom he has killed, although the man killed is no more a man; and, in the same manner, a son is habitually related to his father, even after his father's death; for he is still the same son of the same father, and it would be absurd to pretend that he has lost his own relativity and ceased to be a real son only because his father is no more. It must be remarked, however, that this habitual relativity cannot be real, except when the relation has an intrinsic foundation. For when the foundation is extrinsic, there is nothing formally remaining in the subject which, after the suppression of the term, can keep up its relativity. Thus, if the moon were annihilated, the distance from the earth to the moon would totally vanish, as every one will easily admit.
Much might be said about predicamental relations, both intrinsic and extrinsic; but, in a general treatise like this, we cannot well enter into matters of detail. We will only state that relations are divided according to their foundations. Intrinsic relations are respectively founded on substance, on action and passion, on quality, and on quantity; and therefore may be reduced to four kinds. Extrinsic relations also may be divided into four kinds, as they are respectively founded on a common cause, on a common region of ubication, on a common duration, or on a common extrinsic term of comparison.
Substance, and everything else considered absolutely, founds the relations of unity and plurality. Action and passion found the relations of causality and dependence. Quality founds the relations of likeness or unlikeness. Quantity founds the relations of equality or inequality. All these relations are called intrinsic, because their foundation is something intrinsic to the terms related.
A common cause founds the relation which we may call of collateralness between two terms proceeding from it. Thus two brothers are connected in mutual fraternity, inasmuch as they are the offspring of the same parents. A common region of ubication and movement founds the relation of distance. A common duration founds the relation of succession. A common extrinsic term of comparison founds the relation of site or situation. All these relations are called extrinsic, because their foundation is extrinsic to the terms related.
Principles of real distinction.
Distinction is nothing but a negation of identity; and therefore there must be as many kinds of [pg 297] distinction as there are kinds of identity which can be denied. Hence we cannot properly determine the principles of real distinction without first ascertaining what are the principles of real identity.
Identity is a relative unity, or a relation founded on the unity of a thing. For the thing which is to be styled the same must be compared with itself according to that entity on account of which it is to be pronounced to be identical with itself; and it is evident that such an entity must be one in order to be the same. Thus if I say: “The pen with which I am now writing is the very same which I used yesterday,” the pen with which I am now writing will be the subject of the relation, the pen which I used yesterday will be the term of the relation, and the oneness of its entity will be the foundation of the relation and the formal reason of the identity.
As relations, like everything else, are specified by their formal reasons, it is clear that there must be as many kinds of identity as there are kinds of unities on which the relation of identity can be founded. Now, three kinds of unities can be conceived: first, the formal unity of a complete being, or a complete unity, which may be called physical unity; secondly, the unity of an incomplete or metaphysical reality, which may be called metaphysical unity; thirdly, the unity of a being of reason, which may be called logical unity. Accordingly, there can be three kinds of identity, viz., the physical, the metaphysical, and the logical. Let us say a word about each.
Physical identity is a relation founded on the unity of a physical entity, and is the most real of all identities. Some philosophers taught that this identity is merely a logical relation, or a relation of reason, because a relation cannot be real unless its subject be really distinct from its term—a condition which cannot be verified when the subject and the term are identical. But they did not reflect that a thing must be called really identical with itself then only when it cannot be really distinguished from itself, and inasmuch as it excludes real distinction from itself. It is therefore manifest that real identity excludes real distinction in that in which there is identity. Nevertheless, the thing which is substantially identical with itself may still really differ from itself in the manner of its being, and may, as the subject of the relativity, involve a real entity, which it does not involve as the term of the same relativity; and accordingly the substantial identity of a thing with itself does not exclude all real distinction. The pen with which I am now writing, although identical with the pen that lay on the table one hour before, is now in different accidental conditions, and has some real mode, which was wanting one hour ago. And this shows that there can be a sufficient real distinction between the subject and the term of the relation, even though they are substantially identical.