Isaac Asimov

"[W]hen people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together."

Sam Harris

"Nothing that a Christian and a Muslim can say to each other
will render their beliefs mutually vulnerable to discourse, because
the very tenets of their faith have immunized them against the power of conversation. Believing strongly, without evidence, they have kicked themselves loose of the world. It is therefore in the very nature of faith to serve as an impediment to further inquiry."

David Hume

"In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. A wise man, therefore, proportions his belief to the evidence."

Julian Huxley

I recall the story of the philosopher and the theologian. The two were engaged in disputation and the theologian used the old quip about a philosopher being like a blind man, in a dark room, looking for a black cat--which wasn't there. "That may be," said the philosopher; "but a theologian would have found it."

Denis Diderot

"Scepticism is the first step towards truth."

Carl Sagan

"The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge, and there's no place for it in the endeavor of science. We do not know beforehand where fundamental insights will arise from about our mysterious and lovely solar system. The history of our study of our solar system shows us clearly that accepted and conventional ideas are often wrong, and that fundamental insights can arise from the most unexpected sources."

Bertrand Russell

"Most of the greatest evils that man has inflicted upon man have come through people feeling quite certain about something which, in fact, was false."