Epistemology, or the theory of knowledge, is that branch of philosophy which is concerned with the nature and scope of knowledge, its presuppositions and basis, and the general reliability of claims to knowledge. The pre-Socratic philosophers, the first philosophers in the Western tradition, did not give any fundamental attention to this branch of philosophy, for they were primarily concerned with the nature and possibility of change. They took it for granted that knowledge of nature was possible, although some of them suggested that knowledge of the structure of reality could better come from some sources than from others. Thus, Heraclitus emphasized the use of the senses, and Parmenides in effect stressed the role of reason. But none of them doubted that knowledge of reality was possible. It was not until the fifth century BCE that such doubts began to emerge, and the Sophists were...