Condition (philosophy)

Comprehensive treatment of the word "condition" requires emphasizing that it is ambiguous in the sense of having multiple normal meanings and that its meanings are often vague in the sense of admitting borderline cases.

According to the 2007 American Philosophy: an Encyclopedia, in one widely used sense, conditions are or resemble qualities, properties, features, characteristics, or attributes. In these senses, a condition is often denoted by a nominalization of a grammatical predicate: 'being equilateral' is a nominalization of the predicate 'is equilateral'. Being equilateral is a necessary condition for being square. Being equilateral and being equiangular are two necessary conditions for being a square. In order for a polygon to be a square, it is necessary for it to be equilateral—and it is necessary for it to be equiangular. Being a quadrangle that is both equilateral and equiangular is a sufficient condition for being a square. In order for a quadrangle to be a square, it is sufficient for it to be both equilateral and equiangular. Being equilateral and being equiangular are separately necessary and jointly sufficient conditions for a quadrangle to be a square. Every condition is both necessary and sufficient for itself. The relational phrases 'is necessary for' and 'is sufficient for' are often elliptical for 'is a necessary condition for' and 'is a sufficient condition for'. These senses may be called attributive; other senses that may be called instrumental, causal, and situational are discussed below.

Every condition applies to everything that satisfies it. Every individual satisfies every condition that applies to it. The condition of being equilateral applies to every square, and every square satisfies the condition of being equilateral. The satisfaction relation relates individuals to conditions, and the application relation relates conditions to individuals. The satisfaction and application relations are converses of each other. Necessity and sufficiency, the relations expressed by 'is a necessary condition for' and 'is a sufficient condition for', relate conditions to conditions, and they are converses of each other. Every condition necessary for a given condition is one that the given condition is sufficient for, and conversely.

As a result of a chain of developments tracing back to George Boole and Augustus De Morgan, it has become somewhat standard to limit the individuals pertinent to a given discussion. The collection of pertinent individuals is usually called the universe of discourse, an expression coined by Boole in 1854. In discussions of ordinary Euclidean plane geometry, for example, the universe of discourse can be taken to be the class of plane figures. Thus, squares are pertinent [individuals], but conditions, propositions, proofs, and geometers are not. Moreover, the collection of pertinent conditions is automatically limited to those coherently applicable to individuals in the universe of discourse. Thus, triangularity and circularity are pertinent [conditions], but truth, validity, rationality, bravery, and sincerity are not.

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