"Monads have no windows through which anything could enter or depart."

"The world is not a machine. Everything in it is force, life, thought."

"I hold that the mark of a genuine idea is that its possibility can be proved, either a priori by conceiving its cause or reason, or a posteriori when experience teaches us that it is actual in nature."

"Time is the order of successive phenomena."

"All the different classes of beings which taken together make up the universe are, in the ideas of God who knows distinctly their essential gradations, only so many ordinates of a single curve so clos…"