After Greek philosophy had run out during about a hundred and fifty years in this sort of vague and imaginative speculation upon the physical world, it underwent a great change, which marks the transition to its second period. These successive opinions of philosophers led a class of men who arose at Athens about the middle age of Socrates to the conclusion, that it would be more profitable to turn the course of human thought from such cosmological reveries to the question of the perception itself of truth by man. He who accomplished this was Socrates, who turned his reflexion by preference upon man himself as the subject who thinks and wills.(335) And herein his character had an influence over Greek philosophy which is strikingly marked through the whole of its second period. This period embraces the Sophists, Socrates himself, Plato and Aristotle, and the Stoics and Epicureans; finally those Sceptic and Eclectic schools which rose naturally from the criticism detecting what is untenable in preceding systems. During the six hundred years which elapse from the teaching career of Socrates to the death of Marcus Antoninus we may say that one great line of inquiry occupied among philosophers the human mind; it was man himself, as the subject of logical thought and moral will.(336) The chief endeavour was to form a science of ethics, and a science of reasoning, to which physical and mathematical studies, though at times warmly pursued and never wholly neglected, were yet subordinate.(337)