" The very essence of things is totally changed. You neither are agreed upon the definition of the soul nor on that of matter. Descartes, as I observed in my last, maintains that the soul is the same thing with thought, and Mr. Locke has given a pretty good proof of the contrary. Descartes asserts farther, that extension alone constitutes matter, but Sir Isaac adds solidity to it. How furiously contradictory are these opinions! Non nostrum inter vos tantas componere lites (Virgil). "

― Voltaire , Letters on England