28 On Descriptive Definition
On Descriptive Definition only of things predicable of a subject; therefore, Damascene must be calling things predicable of a descriptum accidents; and these can only be concepts, spoken words, or written words.
It follows that a description and its descriptum are not always convertible; for since accidents are only contingently predicable of something, it is possible that the descriptum be predicated of a subject but not the description. But this is always due to some imperfection in that of which the descriptum is predicated. Thus, man can be described as follows: man is a biped having two hands, and, of course, one could enlarge on this description by adding features that belong only to man. But even when that is done it is still possible that there be an object of which the description is false, but the descriptum true—a man, for example, who lacks hands. The reason for this is that the individual involved is not perfect.
Nevertheless, 'description' can be used in two senses, one broad and the other narrow. The doctor uses the term in the broad sense. In the narrow sense a description is composed only of properties so that a description and its descriptum are always convertible.
28: On Descriptive Definition A descriptive definition is one composed of both substantial and accidental items. To use the example Damascene cites in the book referred to, "Man is a rational animal, walking erectly, and having broad nails'. Thus, some complex expressions are composed of things predicable in the first mode of perseity
(definitions); others are composed of things that are not predicable in the first mode of perseity (descriptions), and still others are composed of both; these we call descriptive definitions. But, of course, since each definition, description, and descriptive definition is an expression, none is really identical with the definitum or descriptum; they do, however, signify the same thing.
29: On Definitum Next we shall consider the notions of definitum and descriptum. 'Definitum' has two senses. In the first sense a definitum is that whose parts or essence is