The differences relate to many details, but the crucial difference is in a fundamentally different understanding of the task of philosophy. Wittgenstein believed that the task of philosophy was to clean up linguistic mistakes. Russell was ultimately concerned with establishing sound epistemological foundations. Epistemological questions such as how practical knowledge is possible did not interest Wittgenstein. Wittgenstein investigated the "limits of the world" and later on meaning. For Wittgenstein, metaphysics and ethics were nonsensical - as they did not "speak of facts" - though he did not mean to devalue their importance in life by describing them in this way. Russell, on the other hand, believed that these subjects, particularly ethics, though belonging not to philosophy nor science and possessing an inferior epistemological foundation, were not only of certain interest, but also meaningful.