Section 18

That in virtue of which has various meanings. (a) The form or essence of each individual thing; e.g., that in virtue of which a man is good is goodness itself. (b) The immediate substrate in which a thing is naturally produced; as, e.g., color is produced in the surface of things. Thus that in virtue of which in the primary sense is the form , and in the secondary sense, as it were, the matter of each thing, and the immediate substrate.

And in general that in virtue of which will exist in the same number of senses as cause. For we say indifferently in virtue of what has he come? or for what reason has he come? and in virtue of what has he inferred or inferred falsely? or what is the cause of his inference or false inference? (And further, there is the positional sense of καθ’ ὅ, in which he stands, or in which he walks; all these examples denote place or position.)

Hence in virtue of itself must also have various meanings. It denotes (a) The essence of each particular; e.g., Callias is in virtue of himself Callias and the essence of Callias. (b) Everything contained in the definition; e.g., Callias is in virtue of himself an animal, because animal is present in the definition, since Callias is a kind of animal.

(c) Any attribute which a thing has received directly in itself or in any of its parts; e.g., the surface is white in virtue of itself; and man lives in virtue of himself, because the soul is a part of the man, and life is directly contained in it. (d) That which has no other cause. Man has many causes: animal, twofooted, etc.; but nevertheless man is in virtue of himself man. (e) All things which belong to a thing alone and qua alone; and hence that which is separate is in virtue of itself. 1