Full Idea
If a triangle exists, there must be a reason or cause why it exists; and if it does not exist, there must be a reason or cause which hinders its existence or which negates it.
Gist of Idea
There must always be a reason or cause why some triangle does or does not exist
Source
Baruch de Spinoza (The Ethics [1675], I Pr 11)
Book Reference
Spinoza,Benedict de: 'Ethics', ed/tr. White,WH/Stirling,AH [Wordsworth 2001], p.10
A Reaction
Hm. Spinoza is setting up a defence of the ontological argument, which seems to require that he lower his normal high standards of argument.