Property (Gr. ἵδιον, Lat. proprium ), one of the five predicables described in the Isagoge of porphyry, designates an attribute or characteristic that is peculiar to a thing of a certain type. It is important in the logic of definition. In examining the differences that can be used to distinguish a given species classified within a common genus and thus to help in formulating the definition of the species, one discovers several kinds. (1) Common differences predicate no more than some otherness in the condition of the subject; e.g., Plato as an adult differs from himself as a boy. They are called predicable accidents; if used in formulating definitions, several must be used in a conjunction proper to the species. (2) A more proper difference is an accident that is inseparable from an individual, that belongs to him and is proper only to him (e.g., a scar, an aquiline nose). (3) The most proper differences are those that are commensurable with the specific nature; any one of these will serve to differentiate a nature. The difference that is the most proper determination by which a nature may be designated, and is also the reason for all other proper differences, is given a special name, specific difference (e.g., rational as said of man). The other proper differences that are outside the nature but follow necessarily on it, and are convertible with it, retain the more generic name of property or proprium. This is defined as the universal said of a species as belonging only, necessarily, and always to that species, and to every individual of that species.
Properties in this strict sense may follow either on the specific nature or on generic natures to the extent that these are definable by a difference. For example, having a nervous system is a property of the genus, animal, following on sensibility. In a broader sense property is frequently understood as designating an attribute that belongs to something always, but neither only, nor necessarily (e.g., two-footed, as said of man).
In the logic of reasoning property also designates one of the four kinds of predicates enumerated by aristotle in his Topics (101b 11–37; 128b 14–139a 20) as constituting one type of dialectical problem.
In strict scientific reasoning, i.e., that which employs a proper cause, properties are demonstrated of their subject through the real definition of the subject (see demonstration). Predication of an attribute of its proper subject is the second mode of per se predication (Anal. post. 73a 35–73b 24). The aim of science is to reduce attributes to their proper cause, so far as this is possible. The methodology of each science must determine the kind of property to be proved of the subject of the science, the causes through which they are to be proved, and in what order this is to be done.
See Also: dialectics; methodology (philosophy); logic.
Bibliography: v. miano, Enciclopedia filosofica, 4 v. (Venice–Rome 1957) 3:1168–70. p. foulquiÉ and r. saint–jean, Dictionnaire de la langue philosophique (Paris 1962) 584–585. r. eisler, Wörterbuch der philosophischen Begriffe, 3 v. (4th ed. Berlin 1927–30) 1:301–303.