A thing is not proved just because no one has ever questioned it. What has never been gone into impartially has never been properly gone into. Hence skepticism is the first step toward truth. It must be applied generally, because it is the touchstone.

Denis Diderot (1713-1784) French editor, philosopher

Pensées Philosophiques [Philosophical Thoughts] (1746)

Alt trans.: "The first step towards philosophy is incredulity."