Full Idea
Whatever ideas follow in the mind from ideas which are adequate in the mind are also adequate.
Gist of Idea
If our ideas are adequate, what follows from them is also adequate
Source
Baruch de Spinoza (The Ethics [1675], II Pr 40)
A Reaction
This appears to be Modus Ponens, and he calls it (in Sch 1) 'the foundations of our reasoning'. If 'adequate' ideas are knowledge, then this also seems to say that knowledge is closed under known implication.
Book Reference
Spinoza,Benedict de: 'Ethics', ed/tr. Curley,Edwin [Penguin 1996], p.55