  One might reasonably depict the earliest period of Heidegger's philosophical work, in Freiburg (1915–23) and Marburg (1923–6), before he commenced the writing of Being and Time itself, as the pre-history of that seminal text (although for an alternative analysis that stresses not only a back-and-forth movement in Heidegger's earliest thought between theology and philosophy, but also the continuity between that earliest thought and the later philosophy, see van Buren 1994, 2005). Viewed in relation to Being and Time, the central philosophical theme in these early years is Heidegger's complex critical relationship with Husserl's transcendental phenomenology—what Crowell (2005, p.49) calls “a dynamic of attraction and repulsion”—as driven by Heidegger's transformative reading of Aristotle. As early as a 1919 lecture course, for example, we find Heidegger arguing that Husserl's view (developed in the Logical Investigations, Husserl 1900/1973), that philosophy should renounce theory and concentrate on the things given directly in consciousness, is flawed because such givenness is itself a theoretical construct. For the young Heidegger, then, it is already the case that phenomenological analysis starts not with Husserlian intentionality (the consciousness of objects), but rather with an interpretation of the pre-theoretical conditions for there to be such intentionality. This idea will later be central to, and elaborated within, Being and Time, by which point a number of important developments (explained in more detail later in this article) will have occurred in Heidegger's thinking: the Husserlian notion of formal ontology (the study of the a priori categories that describe objects of any sort, by means of our judgments and perceptions) will have been transformed into fundamental ontology (a neo-Aristotelian search for what it is that unites and makes possible our varied and diverse senses of what it is to be); Husserl's transcendental consciousness (the irreducible thinking ego or subject that makes possible objective inquiry) will have been transfigured into Dasein (the inherently social being who already operates with a pre-theoretical grasp of the a priori structures that make possible particular modes of Being); and Husserlian intentionality (a consciousness of objects) will have been replaced by the concept of care or Being-in-the-world (a non-intentional, or perhaps pre-intentional, openness to a world). 