### Single Idea 4739

#### [catalogued under 1. Philosophy / F. Analytic Philosophy / 3. Analysis of Preconditions]

Full Idea

Necessary and sufficient conditions are usually expressed by "if and only if" (abbr. "iff"), where "if" is the sufficient condition, and "only if" is the necessary condition.

Gist of Idea

In "if and only if" (iff), "if" expresses the sufficient condition, and "only if" the necessary condition

Source

Pascal Engel (Truth [2002], §1.1)

Book Reference

Engel,Pascal: 'Truth' [Acumen 2002], p.14

A Reaction

'I take my umbrella if and only if it is raining' (oh, and if I'm still alive). There may be other necessary conditions than the one specified. Oh, and I take it if my wife slips it into my car…

Related Idea

Idea 3891
If p entails q, then p is sufficient for q, and q is necessary for p **[Scruton]**