Philosophers have not been sceptical only about metaphysics or religious beliefs. There are a great number of other beliefs generally held which they have had at least as much difficulty in justifying, and in the present article I ask questions as to the right philosophical attitude to these beliefs in cases where to our everyday thought they seem so obvious as to be a matter of the most ordinary common sense. A vast number of propositions go beyond what is merely empirical and cannot be seen to be logically necessary but are still believed by everybody in their daily life. Into this class fall propositions about physical things, other human minds and even propositions about one's own past experiences based on memory, for we are not now ‘observing’ our past. The phenomenalist does not escape the difficulty about physical things, for he reduces physical object propositions, in so far as true, not merely to propositions about his own actual experience but to propositions about the experiences of other human beings in general under certain conditions, and he cannot either observe or logically prove what the experiences of other people are or what even his own would be under conditions which have not yet been fulfilled. What is the philosopher to say about such propositions? Even Moore, who insisted so strongly that we knew them, admitted that we did not know how we knew them. The claim which a religious man makes to a justified belief that is neither a matter of purely empirical perception nor formally provable is indeed by no means peculiar to the religious. It is made de facto by everybody in his senses, whether or not he realizes that he is doing so. There is indeed a difference: while everyone believes in the existence of other human beings and in the possibility of making some probable predictions about the future from the past, not everybody holds religious beliefs, and although this does not necessarily invalidate the claim it obviously weakens it.