“ In logic, definition consists in determining the qualities which belong to given concepts or universals; it is not concerned with individuals, which are marked by an infinity of peculiarities, any one or all of which might be predicated of another individual. Individuals can be defined only in so far as they belong to a single kind. According to Aristotle, definition is the statement of the essence of a concept (ὁρισμὸς μὲν γὰν τοῦ τί ἐστι καὶ οὐσίας, Posterior Analytics, B iii. 90 b 30) ”

“ The definition must be equivalent or commensurate with that which is defined; it must be applicable to all the individuals included in the concept and to nothing else. Every man, and nothing else, is a rational animal. “Man is mortal” is not a definition, for mortality is predicable of irrational animals. (2) The definition must state the essential attributes; a concept cannot be defined by its accidental attributes ”