turrets to its foundations. In a sense, we may say that philosophical
thought is not natural, for he who is examining the assumptions upon
which all our ordinary thought about the world rests is no longer in
the world of the plain man. He is treating things as men do not
commonly treat them, and it is perhaps natural that it should appear to
some that, in the solvent which he uses, the real world in which we all
rejoice should seem to dissolve and disappear.

I have said that it is not the task of reflective thought, _in the
first instance_, to extend the limits of our knowledge of the world of
matter and of minds. This is true. But this does not mean that, as a
result of a careful reflective analysis, some errors which may creep
into the thought both of the plain man and of the scientist may not be
exploded; nor does it mean that some new extensions of our knowledge
may not be suggested.

In the chapters to follow I shall take up and examine some of the
problems of reflective thought. And I shall consider first those
problems that present themselves to those who try to subject to a
careful scrutiny our knowledge of the external world. It is well to
begin with this, for, even in our common experience, it seems to be
revealed that the knowledge of material things is a something less
vague and indefinite than the knowledge of minds.




II. PROBLEMS TOUCHING THE EXTERNAL WORLD