The being of Dasein is being-in-the-world. Dasein is not a worldless subject. Heidegger now wants to show that Dasein is not an isolated subject. (In fact Dasein is not, strictly speaking, a subject at all.) It is not just a matter of its being the case that I am not the only one of my kind. My being is essentially being-with-others. If this is so then another traditional problem of philosophy, the problem of our knowledge of other minds, turns out to be a pseudo-problem.

The traditional ‘problem’ arises from the assumption that I can only be directly aware of my own mind and its contents. Any knowledge I have of other minds is necessarily indirect. Assuming that it is possible to have knowledge of physical objects through sense-perception, I become aware that some of the physical objects I encounter resemble, both in appearance and behaviour, my own body. On the basis of this resemblance I infer the existence of a mind or consciousness like my own ‘behind’ the other body and its behaviour. The problem with such an analogical inference is that, in the nature of the case, it can only rest on a single case. I cannot use as a premise a generalisation to the effect that whenever I have encountered a body like my own it has been associated with consciousness, because this association is known only in my own case.