Note 2 — Chapter V

Footnote 2: The history of the definition of the Proprium is an example of the tendency of distinctions to become more minute and at the same time more purposeless. Aristotle's ῐδιον was an attribute, such as the laugh of the man or the bark of the dog, common to all of a class and peculiar to the class (quod convenit omni soli et semper) yet not comprised in the definition of the class. Porphyry recognised three varieties of ῐδια besides this, four in all, as follows:—(1) an attribute peculiar to a species but not possessed by all, as knowledge of medicine or geometry; (2) possessed by a whole species but not peculiar to it, as being a biped in man; (3) peculiar to a species, and possessed by all at a certain time, as turning grey in old age; (4) Aristotle's "proprium," peculiar and possessed by all, as risibility. The idea of the Proprium as deducible from or consequent on the essence would seem to have originated in the desire to find something common to all Poryphyry's four varieties.