Being-there, being-with, and being-a-part: Heidegger’s mereology of <italic>Mitsein</italic> in <italic>Being and Time</italic>.

The main problem in making sense of <italic>Mitsein</italic> as an aspect of Dasein in <italic>Being and Time</italic> concerns the sense in which individual Dasein is an ‘I’, given that it can be either an ‘anyone-self’ or an ‘authentic self’. Though it is clear that the anyone-self relates directly to <italic>das Man</italic>, the relation of the authentic self to others is debatable. In this paper, I reexamine the relations between self and others by making sense of the referent of each mode of selfhood, with special attention to the problem of explaining the relations between the two. The problem, I claim, can be solved by bringing into relief a certain conception of <italic>mereology</italic> (theory of parthood relations) that underlies Heidegger’s arguments. As I will demonstrate, Heidegger uses a mereological terminology that appropriates Husserl’s logic of parts and wholes from the <italic>Logical Investigations.</italic> In view of this, I suggest understanding individual Dasein, both <italic>qua</italic> anyone-self and <italic>qua</italic> authentic self, as a <italic>moment</italic>, i.e. a dependent part of an open-ended whole. The apparent gap between anyone-self and authentic self can be better understood as a shift of focus between two different aspects of being the same type of dependent part of a whole. [ABSTRACT FROM AUTHOR]