Since these things are so, and since men possess the power of reflection in very varying degree, it is not surprising that we find it worth while to turn back and study the thoughts of those who have had a genius for reflection, even though they lived at a time when modern science was awaiting its birth. Some things cannot be known until other things are known; often there must be a vast collection of individual facts before the generalizations of science can come into being. But many of the problems with which reflective thought is still struggling have not been furthered in the least by information which has been collected during the centuries which have elapsed since they were attacked by the early Greek philosophers. Thus, we are still discussing the distinction between "appearance" and "reality," and many and varied are the opinions at which philosophers arrive. But Thales, who heads the list of the Greek philosophers, had quite enough material, given in his own experience, to enable him to solve this problem as well as any modern philosopher, had he been able to use the material. He who is familiar with the history of philosophy will recognize that, although one may smile at Augustine's accounts of the races of men, and of the spontaneous generation of small animals, no one has a right to despise his profound reflections upon the nature of time and the problems which arise out of its character as past, present, and future. The fact is that metaphysics does not lag behind because of our lack of material to work with. The difficulties we have to face are nothing else than the difficulties of reflective thought. Why can we not tell clearly what we mean when we use the word "self," or speak of "knowledge," or insist that we know an "external world"? Are we not concerned with the most familiar of experiences? To be sure we are--with experiences familiarly, but vaguely and unanalytically, known and, hence, only half known. All these experiences the great men of the past had as well as we; and if they had greater powers of reflection, perhaps they saw more deeply into them than we do. At any rate, we cannot afford to assume that they did not. One thing, however, I must not omit to mention. Although one man cannot turn over bodily the results of his reflection to another, it by no means follows that he cannot give the other a helping hand, or warn him of dangers by himself stumbling into pitfalls, as the case may be. We have an indefinite advantage over the solitary thinkers who opened up the paths of reflection, for we have the benefit of their teaching. And this brings me to a consideration which I must discuss in the next section.