30 On Subject
On Subject expressed by a definition; in this sense, it is particular substances that are defined. Thus the definition 'rational animal' is a definition of all men because the essence of all men is designated by that definition. The definition designates essence of nothing except particular men, for the only things that are rational animals are individuals like this man and that man. Using 'definitum' in this sense it should be granted that the particular substance is defined.
'Definitum' is used in another way for that which is convertible with the definition and of which the definition is truly predicated. In this sense the definitum is an expression which is convertible with the definition and which signifies exactly the same thing as the definition. Using 'definitum' in this sense singular things are not defined. Only the species is defined, for it is only the species and not the particular which is convertible with the definition; no particular is.
Employing this distinction we have the tools for glossing the texts of Aristotle and his commentator, for some of these texts say that definition is of singulars while others say that species are the things defined.
The same sort of distinction should be drawn in the case of 'descriptum?.
That term can be used for an expression of which the description is first and foremost predicated, standing for the thing described and not for itself; or it can be used for the thing designated by the name and the relevant description.
30: On Subject We have discussed terms which, like 'definition' and 'description' are not applied to universals taken singly. As we noted no one universal by itselfis a definition or a description; every definition or description is composed of several universals. Next we shall consider terms like 'subject', 'predicate', etc., that apply in the case of every universal.
First, as Damascene says in chapter 8 of his Logic, " 'Subject' is used in two senses; there is the subject with respect to existence and the subject with respect to predication. As regards existence, we say that a substance is subject for its accidents; for they can exist only in substance; without substance they cannot exist. The subject of predication, on the other hand, is the particular."!
From these remarks we can see that something is called a subject because it really underlies something that inheres in it and is actually present in it. Used
'[bid., chapter 8, 21-26.