The pre-Socratic Greek philosophers were active before Socrates or contemporaneously, but expounding knowledge developed earlier. The popularity of the term originates with Hermann Diels' work Die Fragmente der Vorsokratiker (The Fragments of the Pre-Socratics, 1903). Major analyses of Pre-Socratic thought have been made by Gregory Vlastos, Jonathan Barnes, Gordon Clark, and Friedrich Nietzsche in his Philosophy in the Tragic Age of the Greeks. It may sometimes be difficult to determine the ac… (More on Pre-socratics)