The obstacles to peace are not obstacles in matter, in inanimate nature, in the mountains which we pierce, in the seas across which we fly. The obstacles to peace are in the minds and hearts of men.
In the study of matter we can be honest, impartial, true. That is why we succeed in dealing with it. But about the things we care for — which are ourselves, our desires and lusts, our patriotisms and hates — we find a harder test of thinking straight and truly. Yet there is the greater need. Only by intellectual rectitude and in that field shall we be saved. There is no refuge but in truth, in human intelligence, in the unconquerable mind of man.

Peace and the Public Mind (1935)