that the thread guiding us in clarifying everyday time (and that is to lead us to original time) is itself securely grounded.21 
* * *
§19. Preparatory considerations toward attaining an original understanding of time. A return to the history of the philosophical interpretation of the concept of time
Our goal is an ur-temporal analysis of care. So we began by determining the time-character of those moments that first push to the fore as time-determinations in the structure of care, namely, already-familiar-with in being-ahead-of-oneself. First we drew our attention to the moments of “already” and “before/ahead of,” and in so doing we remained oriented to characterizing the kind of time that is accessible in the everyday experience of time. We focused on the common concept of time because it is the only one that has been theoretically and conceptually worked out in philosophy heretofore (although only within certain limits).
Characterizing the common concept of time entails understanding time in terms of the now. The now plays a preeminent role in the common understanding of time insofar as we determine the other two time-characteristics—past and future—in relation to it, the past as the no-longer-now, and the future as the not-yet-now. So the now-relation is essential for understanding the past and the future.
As regards the understanding of time as now-time, we can determine something as temporal only insofar as its kind of being is mere presence, that is, only insofar as we understand the thing as having that kind of being. Given the very meaning of its being, only a being that has the character of mere presence has the intrinsic possibility of passing sequentially through a now.
We also say that a being falls within time, or more exactly that at any given moment it falls within a now. So we can reverse the proposition. If something’s time-determination is “falling within a now,” its kind of being is mere presence. The being of the merely present pertains primarily to the world, that is, to nature. World and nature are not identical. World is the categorially broader concept, rather than nature being the broader concept and  world a determined section of it. No, nature is the world only insofar as it is uncovered in a determinate way.
With our focus set on the common concept of time, we asked: Do the moments of care that we first came up with—“already” and “ahead
21. [Here (Moser, p. 520) Heidegger ends his lecture of Friday, 22 January 1926, to be followed by that of Monday, 25 January.]