Book 5
7
Of things potentially relative, some are further relative in respect of particular times; as, e.g., that which has made or will make is relative to that which has been or will be made. It is in this way that a father is called father of a son; the one has acted, and the other has been acted upon, in a particular way. Again, some things are relative in virtue of a privation of their potentiality; such is the impossible and all similar terms, e.g. the invisible.
8
Thus relative terms which involve number and potentiality are all relative because their very essence contains a reference to something else; but not because something else is related to their essence. But (c) that which is measurable or knowable or thinkable is called relative because something else is related to its essence.
9
For thinkable signifies that there is a thought which thinks it; but thought is not relative to that of which it is the thought (for then the same thing would have been said twice). And similarly sight is the sight of something; not of that of which it is the sight, although this is of course true—it is relative to some color or other similar thing.
10
To describe it in the other way—the sight of the object of sight—would be to say the same thing twice. Things, then, which are called relative of their own nature are so called, some in these senses, and others because the classes which contain them are of this kind. E.g., medicine is reckoned as relative because its genus, science, is thought to be a relative thing.
11
Further, there are the properties in virtue of which the things which possess them are called relative; e.g., equality is relative because the equal is relative, and similarity because the similar is relative. Other things are accidentally relative; e.g., a man is relative because he happens to be double something else, and double is a relative term; or white is relative if the same thing happens to be white as well as double.
