Full Idea
If p entails q, then p is sufficient for q, and q is necessary for p.
Clarification
'Sufficient for q' means it must occur; 'necessary for p' means no p without it
Gist of Idea
If p entails q, then p is sufficient for q, and q is necessary for p
Source
Roger Scruton (Modern Philosophy:introduction and survey [1994], 15.7)
Book Reference
Scruton,Roger: 'Modern Philosophy: introduction and survey' [Sinclair-Stevenson 1994], p.194
Related Idea
Idea 4739 In "if and only if" (iff), "if" expresses the sufficient condition, and "only if" the necessary condition [Engel]