The Winter Semester 1921–22 lecture course is an introduction to the interpretation of Aristotle, which Heidegger will develop in the next semester. This phenomenological interpretation was also the title of a book on which Heidegger worked, from 1922 through 1924. The lecture course is basically a destruction of his earlier work and leads to a new explication of life.
The brief first part on the reception of Aristotle addresses the need for a fundamental clarification of philosophizing to its history on the level of factic life itself, and on the then fashionable reception of Aristotle as a naive epistemologist, and on the problem of the “Greekification” of Christianity.
In the second part, What Is Philosophy?, Heidegger defines philosophy as a phenomenological ontology and develops the intrinsically historical character of ontological research. Ultimately, there is no difference between the ontological and the historical. Philosophizing takes place within a hermeneutic situation that determines the way in which we have philosophy. Since philosophy is not a thing but a fundamental having of the situation of our lives, it demands resolution. We can have philosophy in a genuine way. This kind of having involves an addressing of the object, and is always grounded in a prior claim of already being “had” and standing in relation to something. Philosophy is a way of comportment or intentionality. The threefold sense of intentionality, content sense, actualization sense, and relational sense, is refined, and a fourth meaning is added, the temporalizing sense, which comprehends the other three. Temporalization determines the temporalizing sense. We can either have philosophy in the full-fledged sense that concerns my own existence or as an object of curiosity. The original enactment of philosophy is, in the full stretch of the actualization sense itself, pursuant to the temporalizing sense of always being under way. Philosophizing as a fundamental knowing is nothing other than the radical actualization and enactment of the historicality of life’s facticity.
The third part is an ontological revision of Heidegger’s categories of life, and centers upon demonstrating the inherently historical character of the facticity of life. The primary ontological category of life is care, which is indigenous to life itself. Heidegger begins to rethink his analysis of the environment in terms of using and making, rather than seeing. Ruination, or fallenness, as it will be called later, is the dominant tendency of life.