is the text of a lecture course presented at the University of Freiburg in the winter of 1921–1922, and first published in 1985 as volume 61 of Heidegger's collected works. Preceding the work shows the young Heidegger introducing novel vocabulary as he searches for his genuine philosophical voice. In this course, Heidegger first takes up the role of the definition of philosophy and then elaborates a unique analysis of "factical life," or human life as it is lived concretely in relation to the world, a relation he calls "caring." Heidegger's descriptions of the movement of life are original and striking. As he works out a phenomenology of factical life, Heidegger lays the groundwork for a phenomenological interpretation of Aristotle, whose influence on Heidegger's philosophy was pivotal.