“The skeptic does not mean him who doubts, but him who investigates or researches, as opposed to him who asserts and thinks that he has found.”

“Only he who attempts the absurd is capable of achieving the impossible.”

“Those who believe that they believe in God, but without passion in their hearts, without anguish in mind, without uncertainty, without doubt, without an element of despair even in their consolation, believe only in the God idea, not God Himself.”

“A faith which does not doubt is a dead faith.”

“Faith which does not doubt is dead faith. -Miguel de Unamuno, philosopher and writer (1864-1936)”

“Man is said to be a reasoning animal. I do not know why he has not been defined as an affective or feeling animal. Perhaps that which differentiates him from other animals is feeling rather than reason. More often I have seen a cat reason than laugh or weep. Perhaps it weeps or laughs inwardly — but then perhaps, also inwardly, the crab resolves equations of the second degree.”

“A lot of good arguments are spoiled by some fool who knows what they're talking about.”