PREDICABLES, in logic, are the main types of predicates, or the principal ways in which the predicate of a proposition can be related to its subject. The oldest known doctrine of predi cables is that of Aristotle, but the one that had, and still has, the greatest vogue is that of Porphyry, which is not essentially differ ent from that of Aristotle. According to Porphyry there are five predicables, namely, genus, species, differentia, proprium, accident. These five predicables are obtained as follows. When a predicate is affirmed of a subject it must either express something that is essential to the subject (that is, something in the absence of which the subject would not be called by that name) or not. If the predicate is not essential to the subject it is described as an accident. E.g., "Many Prime Ministers of England are Scots men" (or "Oxford men," or "wealthy," etc.) ; but they need not be. If the predicate is essential, then there are four possibilities. The predicate may state the including class in which the subject is included—e.g., "Prime Ministers are Cabinet Ministers" (or "Rectangles are parallelograms," etc.). In this case the predicate is described as a genus of the subject ; and the subject (if a class-name) is called a species of the predicate. The predicate is called a species in relation to the subject, if the subject is a singular term and the predicate represents this class (e.g., "Mr.
Kellogg is a statesman"), or if the subject is a class-name re stricted by "Some" and the predicate denotes an included class (e.g., "Some members of Parliament are Cabinet Ministers," or "Some rectangles are squares"). Again the predicate may assert of the subject some character, or group of characteristics, which distinguishes (or differentiates) one species of a genus from the other species (e.g., "Squares are equilateral," whereas other rec tangles are not). In this case the predicate is called a differentia (or "difference") of the subject term. Lastly, the predicate may assert of the subject something essential, but different from either its genus or differentia, though derivable from these (e.g., "Equi lateral triangles and equiangular"). In this case it is called a proprium (or "property") of the subject. The predicables are applicable readily enough to ideal objects like those of geometry, but cannot be applied very satisfactorily or usefully to empirical objects. Although they mark distinctions which are very impor tant and useful in connection with many ordinary problems, they play no very important part in modern science, which needs more precise and more numerous distinctions than they mark. See