(T)he increase of known truths stimulates the investigation, establishment, and growth of the arts.

I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.

By denying scientific principles, one may maintain any paradox.

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual.

My dear Kepler, what would you say of the learned here, who, replete with the pertinacity of the asp, have steadfastly refused to cast a glance through the telescope? What shall we make of this? Shall we laugh, or shall we cry?

Names and attributes must be accommodated to the essence of things, and not the essence to the names, since things come first and names afterwards.

See now the power of truth; the same experiment which at first glance seemed to show one thing, when more carefully examined, assures us of the contrary.

I have been in my bed for five weeks, oppressed with weakness and other infirmities from which my age, seventy four years, permits me not to hope release. Added to this (proh dolor! [O misery!]) the sight of my right eye — that eye whose labors (dare I say it) have had such glorious results — is for ever lost. That of the left, which was and is imperfect, is rendered null by continual weeping.

Who would set a limit to the mind? Who would dare assert that we know all there is to be known?