"As man reaches out toward the twenty-first century, he will learn to be suspicious of all ideas that are not formulated so that they can be tested by observation.  He will realize that the history of human thought shows that the ideas of which we are surest are the ones we most need to test.  He will realize that his common sense only mirrors his training and experience.  What seems natural and right to him is usually a reflection of the conditions under which he spent his first decade of life."