Definition
A definition is a statement that identifies the nature of a concept’s units.1 Definition is the final stage of concept-formation.
A proper definition is made of two parts, each of which follows from the nature of concept-formation. When we form a concept, we isolate its units by grasping a distinguishing characteristic. In the definition, this becomes what the medieval Aristotelians called the differentia. Further, we can differentiate only on the basis of a wider characteristic, the CCD, which is shared both by the concretes we are isolating and by the concretes from which we are isolating them. In the definition, this gives rise to the genus.
A definition in terms of genus and differentia is like a logical X ray of a concept. It condenses into a brief, retainable statement the essence of the concept-forming process: it tells us what distinguishes the units and from what they are being distinguished, i.e., within what wider group the distinction is being made. To give the standard example: if we conceptualize man by differentiating men from dogs, cats, and horses, then “animal” would be the genus—“rational,” the differentia.2