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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 Ref
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]
21675 | Some facts are indispensable for an effect, and others actually necessitate the effect [Stoic school, by Cicero] |
13309 | That something is a necessary condition of something else doesn't mean it caused it [Seneca] |
12633 | Definitions often give necessary but not sufficient conditions for an extension [Fodor] |
2963 | There may only be necessary and sufficient conditions (and counterfactuals) because we intervene in the world [Lockwood] |
3891 | If p entails q, then p is sufficient for q, and q is necessary for p [Scruton] |
4739 | In "if and only if" (iff), "if" expresses the sufficient condition, and "only if" the necessary condition [Engel] |
14600 | Analysis aims at secure necessary and sufficient conditions [Schaffer,J] |
20388 | 'Necessary' conditions are requirements, and 'sufficient' conditions are guarantees [Davies,S] |