Logic: The Predicables
There are five ways the predicate of a proposition can be related to its subject: “A predicate may be a genus, specific difference, species, property or accident of its subject. These are called the five ‘predicables’”. (SL) Some of these predicables we already know, but it is useful to review what they are, and the commonalities between them: “The five predicables are a classification of predicates based on the standard of how close the predicate comes to stating the essence of the subject”. (SL)
They are:
Species: The species “states the whole essence of the subject” (SL). It is the the essential definition spoken of in “Logic: Apprehension and Terms”. In the proposition “Man is a rational animal”, “rational animal” is the species. A species is composed of a genus and specific difference.
Specific Difference: This is what makes the species different from all others in its genus. “Rational” is the specific difference of man from all other animals.
Genus: The genus “states the generic or common aspect of the essence of the subject.” (SL) For man, the genus would be “animal”. Jolivet defines it as the idea “immediately superior in terms of extension”. (CdF)
Property: A property is an aspect that is not the definition of the subject, but follows from its essence. A property of man that follows from his rationality is that he can use language.
Accident: An accident is an aspect of a subject that does not follow from its essence, and, if changed, would not affect the essence of the subject. An example of this is having or not having a ring finger. If I removed your ring finger you would still be human1.
As stated previously, strictly speaking individuals cannot be predicated. However, to test whether or not something is an accident it is useful to think about individual cases and whether an individual lacking this or that trait would still be considered a member of the species.