Full Idea
A 'necessary' condition for something's being an X is condition that all Xs must satisfy. ...A 'sufficient' condition for something's being an X is a condition that, when satisfied, guarantees that what satisfies it is an X.
Gist of Idea
'Necessary' conditions are requirements, and 'sufficient' conditions are guarantees
Source
Stephen Davies (The Philosophy of Art (2nd ed) [2016], 2.1)
Book Reference
Davies,Stephen: 'The Philosophy of Art (2nd ed)' [Wiley Blackwell 2016], p.24
A Reaction
By summarising this I arrive at the requirement/guarantee formulation, which I am rather pleased with. What is required for rain, and what guarantees rain?
Related Idea
Idea 20389 A definition of a thing gives all the requirements which add up to a guarantee of it [Davies,S]