All of which proves that our knowledge is not necessarily useless because it is rather dim and vague. It is one thing to use a mental state; it is another to have a clear comprehension of just what it is and of what elements it may be made up. The plain man does much of his thinking as we all tie our shoes and button our buttons. It would be difficult for us to describe these operations, but we may perform them very easily nevertheless. When we say that we know how to tie our shoes, we only mean that we can tie them.
Now, enough has been said in the preceding sections to make clear that the vagueness which characterizes many notions which constantly recur in common thought is not wholly dispelled by the study of the several sciences. The man of science, like the plain man, may be able to use very well for certain purposes concepts which he is not able to analyze satisfactorily. For example, he speaks of space and time, cause and effect, substance and qualities, matter and mind, reality and unreality. He certainly is in a position to add to our knowledge of the things covered by these terms. But we should never overlook the fact that the new knowledge which he gives us is a knowledge of the same kind as that which we had before. He measures for us spaces and times; he does not tell us what space and time are. He points out the causes of a multitude of occurrences; he does not tell us what we mean whenever we use the word "cause." He informs us what we should accept as real and what we should repudiate as unreal; he does not try to show us what it is to be real and what it is to be unreal.
In other words, the man of science extends our knowledge and makes it more accurate; he does not analyze certain fundamental conceptions, which we all use, but of which we can usually give a very poor account.
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.