Bertrand Russell, The Problems of Philosophy

"Is there any knowledge in the world which is so certain that no reasonable man could doubt it?"

"Whoever wishes to become a philosopher must learn not to be frightened by absurdities."

"The man who has no tincture of philosophy goes through life imprisoned in the prejudices derived from common sense, from the habitual beliefs of his age or his nation, and from convictions which have grown up in his mind without the cooperation or consent of his deliberate reason."