Reason
"We can only reason from what is; we can reason on actualities, but not on possibilities." - Bolingbroke
"Reason obeys itself; and ignorance submits to whatever is dictated to it." - Thomas Paine
"I do not feel obliged to believe that the same God who endowed us with sense, reason, and intellect had intended for us to forgo their use." - Galilei, Galileo
"Question with boldness even the existance of God; because, if there be one, he must more approve of the homage of reason than that of blindfold fear." - Jefferson, Thomas (1743-1826)
"Le coeur a ses raisons dont le cerveau ne sait nul. T: 'The heart has its reasons, of which the mind knows nothing.'" - Pascal, Blaise (1623-1662)