The aim of this paper is to restore the interdependent or complementary relationship between self and others against the universalistic one (as I call it) that Kant, for example, once insisted on, by reexamining the concept of so-called "private language." I shall consider some views in speech act theory and pragmatics, since there has often been discussion about such a private occurrence as the speaker's "sincerity." For example, Jürgen Habermas situates it in the speaker's "internal nature" as will be seen later. In my opinion, alter ego is an "ego" because we can empathize (einfühlen) with it, and yet it is "alter" ego because it has some private experiences which we cannot perfectly comprehend.