I'm reading Russell's "The problems of philosophy" and he says that the only thing we can be certain about is the existence of our "Sense-data" which are mainly our thoughts and emotions. I wonder if there is some good argument against the certainty of it.
1There are some very strong arguments against but they go much wider and deep into metaphysics so are difficult to state here. Russell was obviously not a fan of Kant and he dismisses Bradley with a hand-waive. For another view try Bradley's metaphysical essay 'Appearance and Reality'.– user20253Feb 18, 2018 at 14:01