In the second place, the philosopher has the interpretations of experience which he has inherited from his predecessors. The influence of these is enormous. Each age has, to a large extent, its problems already formulated or half formulated for it. Every man must have ancestors, of some sort, if he is to appear upon this earthly stage at all; and a wholly independent philosopher is as impossible a creature as an ancestorless man. We have seen how Descartes (section 60) tried to repudiate his debt to the past, and how little successful he was in doing so. Now, we make a mistake if we overlook the genius of the individual thinker. The history of speculative thought has many times taken a turn which can only be accounted for by taking into consideration the genius for reflective thought possessed by some great mind. In the crucible of such an intellect, old truths take on a new aspect, familiar facts acquire a new and a richer meaning. But we also make a mistake if we fail to see in the writings of such a man one of the stages which has been reached in the gradual evolution of human thought, if we fail to realize that each philosophy is to a great extent the product of the past. When one comes to understand these things, the history of philosophy no longer presents itself as a mere agglomeration of arbitrary and independent systems. And an attentive reading gives us a further key to the interpretation of what seemed inexplicable. We find that there may be distinct and different streams of thought, which, for a while, run parallel without commingling their waters. For centuries the Epicurean followed his own tradition, and walked in the footsteps of his own master. The Stoic was of sterner stuff, and he chose to travel another path. To this day there are adherents of the old church philosophy, Neo-Scholastics, whose ways of thinking can only be understood when we have some knowledge of Aristotle and of his influence upon men during the Middle Ages. We ourselves may be Kantians or Hegelians, and the man at our elbow may recognize as his spiritual father Comte or Spencer. It does not follow that, because one system follows another in chronological order, it is its lineal descendant. But some ancestor a system always has, and if we have the requisite learning and ingenuity, we need not find it impossible to explain why this thinker or that was influenced to give his thought the peculiar turn that characterizes it. Sometimes many influences have conspired to attain the result, and it is no small pleasure to address oneself to the task of disentangling the threads which enter into the fabric.