This Winter Semester 1923–24 lecture course is the first of Heidegger’s courses in Marburg. It is both an introduction to phenomenological research and a critique of Edmund Husserl’s phenomenology of consciousness. Guided by the things themselves, Heidegger develops his conception of a phenomenology of being-there. The course consists of a clarification of phenomenology and a discussion of the initial breakthrough to phenomenological research in Husserl’s Logical Investigations and its ensuing course in modern philosophy.
The first part of the course begins with a clarification of the term “phenomenology” through an interpretation of φαίνομενον and λόγος in Aristotle’s writings. Heidegger shows that Aristotle is concerned with the being of the world and life as being-in-the-world. Modern philosophy, on the other hand, is guided by the care of certain and clear knowledge. The ideal of mathematical strictness makes it impossible for entities to show themselves in their being. In an interpretation of Husserl’s essay, Philosophy as Rigorous Science, Heidegger shows that his conception of phenomenology was still dominated by the care of certain and clear knowledge and the concern for already known knowledge. The concern for certainty and clarity makes the beginning of modern philosophy with Réne Descartes.
In the second part of the course, Heidegger gives an extensive interpretation of the res cogitans in the philosophy of Descartes, which is guided by the question of the meaning of the truth of knowledge. Descartes determines not only truth as certainty, but also retains scholastic ontology. To understand Descartes, Heidegger must also give an explication of truth and being in the philosophy of St. Thomas Aquinas.
In the third part, Heidegger shows how Descartes failed to ask the question of the being of the res cogitans, because his research was dominated by the concern for certain knowledge. Husserl took over from Descartes the ideal of certain and clear knowledge and could therefore not disclose being-there in its being. Where Descartes emphasized the priority of the “I think,” Heidegger underscores the concrete fact that “I am.” Heidegger’s course is not only a destruction of phenomenological research, but also a return to the things themselves, to the facticity of the “I am,” and ultimately, to being-there itself.