The radical novelty of modern science lies precisely in the rejection of the belief, which is at the heart of all popular religion, that the forces which move the stars and atoms are contingent upon the preferences of the human heart. The science of Aristotle and of the Schoolmen, on the other hand, was a truly popular science. It was in its inspiration the instinctive science of the unscientific man. “They read into the cause and goal of the universe,” as Dr. Randall has said, “that which alone [p128] justifies it for man, its service of the good.” They provided a conception of the universe which was available for the religious needs of ordinary men, and in the _Divine Comedy_ we can see the supreme example of what science must be like if it is to satisfy the human need to believe. The purpose of the whole poem, said Dante himself, “is to remove those who are living in this life from the state of wretchedness, and to lead them to the state of blessedness.” Mediæval science, which follows the logic of human desire, was such that Dante could without violence either to its substance or its spirit say at the summit of Paradise: To the high fantasy here power failed; but already my desire and will were rolled—even as a wheel that moveth equally—by the Love that moves the sun and the other stars. This is the great climax which men instinctively expect: the ability to say with perfect assurance that when the truth is fully evident it will be seen that their desire and will are rolled by the love that moves the sun and the other stars. They hope not only to find the will of God in the universe but to know that his will is fundamentally like their own. Only if they could believe that on the basis of scientific investigation would they really feel that science had ‘explained’ the world. Explanation, in this sense, cannot come from modern science because it is not in this sense that modern science attempts to explain the universe. It is wholly misleading to say, for example, that the scientific picture of the world is mechanical. All that can properly be said is that many scientists have found it satisfying to think about the universe as if it were built on a mechanical model. “If I [p129] can make a mechanical model,” said Lord Kelvin, “I can understand it. As long as I cannot make a mechanical model all the way through, I cannot understand it.” But what does the scientist mean by “understanding it”? He means, says Professor Bridgman, that he has “reduced a situation to elements with which we are so familiar that we accept them as a matter of course, so that our curiosity rests.” Modern men are familiar with machines. They can take them apart and put them together, so that even though we should all be a little flustered if we had to tell just what we mean by a machine, our curiosity tends to be satisfied if we hear that the phenomenon, say, of electricity or of human behavior, is like a machine.