Whoever cares to become acquainted with the difficulty of the problem of truth must not be impatient of dialectical subtleties. There is a well-known story in Boswell's _Life of Dr. Johnson_ which relates how the Doctor refuted Berkeley's philosophy which affirmed the non-existence of matter. "I observed," says Boswell, "that though we are satisfied his doctrine is not true, it is impossible to refute it. I shall never forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it--'I refute it _thus_.'" Dr. Johnson is the representative of robust common sense. It has very often turned out in metaphysical disputes that the common-sense answer is the one that has been justified in the end. Those who are impatient of metaphysics are, therefore, not without reasonable ground; and indeed the strong belief that the common-sense view will be justified in the end, however powerful the sceptical doubt that seems to contradict it, however startling the paradox that seems to be involved in it, is a possession of the human mind without which the ordinary {21} practical conduct of life would be impossible. When, then, we ask ourselves, What is truth? the answer seems to be simple and obvious. Truth, we reply, is a property of certain of our ideas; it means their agreement, as falsity means their disagreement, with reality. If I say of anything that it is so, then, if it is so, what I say is true; if it is not so, then what I say is false. This simple definition of truth is one that is universally accepted. No one really can deny it, for if he did he would have nothing to appeal to to justify his own theory or condemn another. The problem of truth is only raised when we ask, What does the agreement of an idea with reality mean? If the reader will ask himself that question, and carefully ponder it, he will see that there is some difficulty in the answer to the simple question, What is truth? The answer that will probably first of all suggest itself is that the idea is a copy of the reality. And at once many experiences will seem to confirm this view. Thus when we look at a landscape we know that the lines of light which radiate from every point of it pass through the lens of each of our eyes to be focussed on the retina, forming there a small picture which is the exact counterpart of the reality. If we look into another person's eye we may see there a picture of the whole field of his vision reflected from his lens. It is true that what we see is not what he sees, for that is on his retina, but the analogy of this with a photographic camera, where we see the picture on the ground glass, seems obvious and natural; and so we think of knowledge, so far as it depends on the sense of vision, as consisting in more or less vivid, more or less faded, copies of real things stored up by the memory. But a very little reflection will convince us that