Pictures, propagated by motion along the fibers of the optic nerves in the brain, are the cause of vision.

Plato is my friend, Aristotle is my friend, but my greatest friend is truth.

Oh Diamond! Diamond! thou little knowest the mischief done! [Apocryphal]

I do not feign hypotheses.

The latest authors, like the most ancient, strove to subordinate the phenomena of nature to the laws of mathematics.

A man may imagine things that are false, but he can only understand things that are true, for if the things be false, the apprehension of them is not understanding.

A Vulgar Mechanick can practice what he has been taught or seen done, but if he is in an error he knows not how to find it out and correct it, and if you put him out of his road he is at a stand. Whereas he that is able to reason nimbly and judiciously about figure, force, and motion, is never at rest till he gets over every rub. (from a letter dated 25 May, 1694)