"There are also two kinds of truths: those of reasoning and those of fact. Truths of reasoning are necessary and their opposite is impossible; truths of fact are contingent and their opposite is possib…"

"There is nothing in the intellect that was not previously in the senses, except the intellect itself."

"For I hold that it is only when we can prove everything we assert that we understand perfectly the thing under consideration."

"The passing condition which involves and represents a multiplicity in the unity, or in the simple substance, is nothing else than what is called perception. This should be carefully distinguished from…"

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