Bad books engender bad habits, but bad habits engender good books.

Doubt is the origin of wisdom

Neither the true nor the false roots are always real; sometimes they are imaginary; that is, while we can always imagine as many roots for each equation as I have assigned, yet there is not always a definite quantity corresponding to each root we have imagined.

The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.

I am thing that thinks: that is, a things that doubts,affirms, denies, understands a few things, is ignorant of many things, is willing, is unwilling, and also which imagines and has sensory perceptions.

Nothing comes out of nothing.

There is a little gland in the brain in which the soul exercises its functions in a more particular way than in the other parts.