On the other hand, it is the task of reflective thought, not in the first instance, to extend the limits of our knowledge of the world of matter and of minds, but rather to make us more clearly conscious of what that knowledge really is.  Philosophical reflection takes up and tries to analyze complex thoughts that men use daily without caring to analyze them, indeed, without even realizing that they may be subjected to analysis.

It is to be expected that it should impress many of those who are introduced to it for the first time as rather a fantastic creation of problems that do not present themselves naturally to the healthy mind.  There is no thoughtful man who does not reflect sometimes and about some things; but there are few who feel impelled to go over the whole edifice of their knowledge and examine it with a critical eye from its 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

CHAPTER III

IS THERE AN EXTERNAL WORLD?

12.  HOW THE PLAIN MAN THINKS HE KNOWS THE WORLD.—­As schoolboys we enjoyed Cicero’s joke at the expense of the “minute philosophers.”  They denied the immortality of the soul; he affirmed it; and he congratulated himself upon the fact that, if they were right, they would not survive to discover it and to triumph over him.

At the close of the seventeenth century the philosopher John Locke was guilty of a joke of somewhat the same kind.  “I think,” said he, “nobody can, in earnest, be so skeptical as to be uncertain of the existence of those things which he sees and feels.  At least, he that can doubt so far (whatever he may have with his own thoughts) will never have any controversy with me; since he can never be sure I say anything contrary to his own opinion.”