We call a verbal statement _proved_ as soon as the connection between it and our present experience has been established in such a manner that the idea of reality is aroused in our mind. The believing of that which has been proved is called _knowing_. Belief is often used in a narrower sense, excluding that which is known and including only that which does not arouse either an idea of reality or an idea of unreality. Both usages are justifiable, the narrower one and also the wider one. Knowledge and belief are opposed as well as related. It is of much practical importance to distinguish that which has been proved from that which has not been proved. But it is also of practical importance to distinguish that which is surely unreal from that which is merely unproved. It is quite impossible in human life to prove every statement before we permit it to affect our thought and our action. The chief thing which a man must have learned when he arrives at maturity is this: that the number of facts to be believed is very much smaller than he thought originally. The belief of childhood and youth is subject to continuous losses. Something is, indeed, confirmed and strengthened by growing experience; but it was believed before it was known, and cannot properly be called an additional belief. Much that has been believed for some time is recognized as unreal. That apparent errors have to be recognized as truths happens much more rarely. Experience makes a man more and more skeptical, cautious. This is of great advantage to him in his adaptation to the world, and higher institutions of learning to a large extent have their purpose in aiding the young to develop cautious, critical habits of thinking. A student goes to college not merely in order to cram himself with bare facts, but to be trained in the habit of seeing men and things in the abundance of their relations, of asking for their passports before granting them free passage. Thus the original tendency to believe is gradually limited, more in one individual, less in another. But it is never perfectly eradicated. This, indeed, would not be advantageous. A limited tendency to believe is indispensable. Two conditions contribute chiefly toward the retention of a belief which can be neither proved nor disproved: authority and personal needs.