Every man is a philosopher. Every man has his own philosophy of life and his special view of the universe. Moreover, his philosophy is important, more important perhaps that he himself knows. It determines his treatment of friends and enemies, his conduct when alone and in society, his attitude towards his home, his work, and his country, his religious beliefs, his ethical standards, his social adjustment and his personal happiness. 　　Nations, too, through the political or military party in power, have their philosophers of thought and action. Wars are waged and revolutions incited because of the clash of ideologies, the conflict of philippics. It has always been so. World War II is but the latest and most dramatic illustration of the combustible nature of differences in social and political philosophy. 　　Philosophy, says Plato, begins with wonder. We wonder about the destructive fury of earthquakes, floods, storms, drought, pestilence, famine, and fire, the mysteries of birth and death, pleasure and pain, change and permanence, cruelly and kindness, instincts and ideals, mind and body, the size of the universe and man’s place in it. Our questions are endless. What is man? What is Nature? What is justice? What is duty? Alone among the animals man is concerned about his origin and end, about his purposes and goals, about the meaning of life and the nature of reality. He alone distinguishes between beauty and ugliness, good and evil, the better and the worse. He may be a member of the animal kingdom, but he is also a citizen of the world of ideas and values. 　　Some of man’s questions have had answers. Where the answer is clear, we call it science or art and move on to higher ground and a new vista of the world. Many of our questions, however, will never have final answers. Men will always discuss the nature of justice and right, the significance of evil, the art of government, the relation of mind and matter, the search for truth, the quest for happiness, the idea of God, and the meaning of reality. 　　The human race has reflected so long and often on these problems that the same patterns of thought recur in almost every age. We should know what these thoughts are. We should know what answers have been suggested by those who have most influenced ancient and modern thought. We shall want to do our own thinking and find our own answers. It is, however, neither necessary nor advisable to travel alone. Others have helped dispel the darkness, and the light they have kindled may also illuminate our way. According to the author, we can trace the root of war in _____.