A definition (ḥadd) is the comprehensive term for anything by which conception is obtained; it is an explanatory statement that, according to some, comprises the real, the formal, and the verbal definitions. Others restrict the word to the real definition alone and merely mention the formal and verbal alongside it as matters outside its scope. Still others apply “definition” to the real and the formal but not to the verbal. Each of these three usages belongs to a particular school, as I have clarified elsewhere and named those who hold them.

With regard to the syllogism: if its matter is certain it is exclusively called a demonstration (burhān); if its premises are simply conceded it is dialectical (jadalī); if they are widely accepted it is rhetorical (khiṭābī); if they appeal to the imagination it is poetic (shiʿrī); and if they are merely specious it is sophistic (sufusṭāʾī). For this reason the demonstrative, the rhetorical, and the dialectical can overlap. Some equate the rhetorical with that which yields probability (ẓannī), while others call it persuasive (iqnāʿī). They possess further terminologies, some in agreement with the usage of the First Teacher, Aristotle, and others in conflict with it, for many of their authors have diverged in numerous respects from their First Teacher’s method. To elaborate on this, however, is not my concern here.

A definition, when real, is composed of essential attributes; otherwise, it must include accidental ones. Each set—essential and accidental—is either shared with something other than the thing defined or distinguishes it from everything else. The shared essential attribute is the genus; the distinguishing essential attribute is the differentia; their combination constitutes the species. The shared accidental attribute is the common accident, and the distinguishing accidental attribute is the property. Some nevertheless use “property” for whatever befalls a species even when it is not common to all its individuals, though such a property does not effect differentiation. Likewise, one may speak of a “species” in a relative sense, for what is a species in relation to what is above it serves as a genus in relation to what is below it. Yet these and similar points are details of logic that are not my present concern, for discussion of what they have said about genus and species belongs elsewhere, not in these cursory remarks.

These, then, are the five universals. Opposite the universal stands the particular, the conception of which precludes any possibility of multiple predication. Discussion of the composite must be preceded by discussion of the simple and of the way a term signifies it.