Full Idea
I call individual things contingent in so far as we discover nothing, whilst we attend to their essence alone, which necessarily posits their existence or which necessarily excludes it.
Gist of Idea
A thing is contingent if nothing in its essence determines whether or not it exists
Source
Baruch de Spinoza (The Ethics [1675], IV Def 3)
Book Reference
Spinoza,Benedict de: 'Ethics', ed/tr. White,WH/Stirling,AH [Wordsworth 2001], p.164
A Reaction
So something could have an essence which determined that it could not exist, which is presumably a contradiction. That's a very strange sort of essence. Presumably all intrinsically contradictory essences are in some way the same.
Related Idea
Idea 17183 Things are impossible if they imply contradiction, or their production lacks an external cause [Spinoza]