In his lecture course from the Summer Semester of 1926, Heidegger examines the development of the key concepts of ancient philosophy beginning with Thales. By examining the central pre-Socratic thinkers Anaximander, Parmenides, and Heraclitus, Heidegger outlines the historical background of Plato’s and Aristotle’s philosophy and their contributions to formulating the question of being. As the centerpiece of this discussion, he addresses the “opposition” between being and becoming as the central problem in the formulation of the question of being throughout Greek philosophy.