Heidegger says concerning the question of the possibility of a proof of the existence of an external world that ‘the “scandal of philosophy” (Kant's words) is not that this proof has yet to be given, but that such proofs are expected and attempted again and again’. Heidegger thinks this because our being (Dasein) is in the world, and this is something which Descartes for one failed to appreciate. I am not concerned here to answer the question whether Heidegger's own views on these matters will do, though I think that they will not. Indeed they might well be said to beg the question at issue, in that Heidegger starts from the presumption that we are actually in the world, even if we are not in it in the way in which the tree in the garden is (and does not this last point make a great difference to the situation?). Another way of reacting to Heidegger would be to say that he does not treat the fact and force of scepticism seriously enough when he makes that presumption. After all, it is possible for us to raise sceptical doubts about the existence of a world apart from ourselves, while it is not possible for the tree in the garden to act similarly. Hence, even if we make the presumption that we are in the world, as Heidegger insists, we are in it in a way that leaves untouched the possibility of sceptical doubts about what that world and our being in it are like. It might, logically, be the case, for example, that the world consists of just me and that my being in the world is no more than for me just to exist. In other words, my being in the world does not directly entail that there exists a world apart from me.