ABSTRACT
It is now often said that philosophical scepticism is not serious, and there is a sense in which this is true. The philosopher who tells us that it is doubtful whether the sun will rise tomorrow is not issuing a warning, in the way that an astronomer might; he is not inviting us to take precautions against a natural catastrophe. The philosopher who protests that he has no good reason for believing that anyone besides himself can think or feel is not any the less ready to sympathize with his fellow men or to pay attention to their views. This is not to say that philosophic doubts of this kind have no influence at all upon the behaviour of those who entertain them. To be unable to see one's way out of the prison of solipsism may well produce a sense of isolation. Yielding to phenomenalism may make the world seem insubstantial: distrust of induction may make it seem perilous. And no doubt there are psychological reasons why philosophers adopt such positions; a psycho-analyst might be able to account for someone's finding these difficulties especially acute. But the point of philosophical scepticism does not lie in its effects; nor would the discovery of its causes, however interesting in itself, enable us to evaluate its content. It rests upon argument: if we wish to understand it, the argument has to be examined.
