Solipsism at Performance Studies international, Stanford University
It is wrong to oppose to objects an isolated ego-subject, without seeing in the Dasein the basic constitution of being-in-the-world; but it is equally wrong to suppose that the problem is seen in principle and progress made toward answering it if the solipsism of the isolated ego is replaced by a solipsism en deux in the I-thou relationship. As a relationship between Dasein and Dasein this has its possibility only on the basis of being-in-the-world. Put otherwise, being-in-the-world is with equal originality both being-with and being-among.
Martin Heidegger, The Basic Problems of Phenomenology