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)

Do not the Rays which differ in Refrangibility differ also in Flexibity; and are they not by their different Inflexions separated from one another, so as after separation to make the Colours in the three Fringes above described? And after what manner are they inflected to make those Fringes?

An object that is at rest will tend to stay at rest. An object that is in motion will tend to stay in motion.

How came the bodies of animals to be contrived with so much art, and for what ends were their several parts? Was the eye contrived without skill in Opticks, and the ear without knowledge of sounds?...and these things being rightly dispatch’d, does it not appear from phænomena that there is a Being incorporeal, living, intelligent...?

What goes up must come down.

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

Atheism is so senseless and odious to mankind that it never had many professors.