Scientists, social scientists and historians are all engaged in different branches of the same study: the study of man and his environment, of the effects of man on his environment and of his environment on man. The object of the study is the same: to increase man's understanding of, and mastery over, his environment. The presuppositions and the methods of the physicist, the geologist, the psychologist and the historian differ widely in detail; nor do I wish to commit myself to the proposition that, in order to be more scientific, the historian must follow more closely the methods of physical science. But historian and physical scientist are united in the fundamental purpose of seeking to explain, and in the fundamental procedure of question and answer.