  A fifth topic of discussion introduced in the Middle Ages through Boethius' Commentaries on Porphyry's Isagoge involves the “predicables” (praedicabilia), which are ways in which predicates relate to subjects. Examples are “accident” (‘black’ in ‘This cat is black’), “species” (‘man’ in ‘Socrates is a man’), and “definition” (‘rational animal’ in ‘Man is a rational animal’) (see Porphyry 1975). Although these issues are originally introduced by Aristotle in the Topics, this work was not available in the Middle Ages until after the period of translations in the twelfth century.