To our usual way of thinking, it seems the most obvious fact that Da-sein can understand others in their being, both as like himself and as other than himself. Ontologically, this fact is a problem that is neither obvious nor easy to explain. In Husserl’s phenomenological [76] school, to which at one time Heidegger belonged, the solution of this problem was thought to lie in “empathy” (Einfuhlung), literally: “feeling oneself into another.” Heidegger rejects this solution, because it assumes that the other is “analogous” to oneself, is a “double’’ of oneself, and leaves unexplained precisely the most difficult problem: How is it possible that this “double” of myself is yet manifest to me as the “other”? (SZ, 124ff.).
This is the problem to which Heidegger offers the solution of being-with. Just as Da-sein is never a worldless subject, but in advance refers himself to the possible presence of things within a world, so he is never an isolated, otherless “I,” but in advance understands himself as I-myself-with-(possible other selves). The “with” already refers him to the other as a self; that is, as one who exists in the same way as he himself and yet is the “other” with whom he can be together in the same world.
The basic structure of being-with cannot be reduced to or explained from anything else. The articulated whole of being-myself-with-(another-self) cannot be melted down into an “inarticulate,” isolated “I,” which then somehow finds its way to another, equally isolated “I.” Da-sein does not have to find his way to another Da-sein, because with the disclosure of his own being as being-with, the being of others is already disclosed and understood. It is true that in everyday being-together-with-others, this primary understanding of the other, as well as of oneself, is often covered over and distorted, so that to know each other requires a “getting-to-know-one-another.” Necessary and unavoidable as such special and explicit efforts may be to disclose oneself to another self, they do not originally constitute being-together-with-one-another but are only possible on the ground of the primary being-with.
Being-with others is a basic structure of each Da-sein’s self, for the sake of which he exists: Da-sein therefore exists essentially for the sake of others. He understands them in advance as the selves who are in the world in the same way as himself: their being has the same character of for the sake of as his own. On the ground of the irreducible with-structure of his being, Da-sein is essentially with-worldish. His world is in advance a world he shares with others; his being-in-the-world is in itself a being-with-others-in-the-world. (p. 75-76)