Man would know very little about the outer world if he had to rely exclusively upon deduction and in- tuition. He would have at hand only a few major premises, namely, those furnished by intuition, and would be able to develop only the so-called pure sciences, by which is meant those sciences, such as mathematics, the truths of which are independent of our sense impressions. Deduction as a source of Imowledge is chiefly valuable when employed in con nection with experience or induction.
15. Experience, or of our knowl edge of the world in which we live has been obtained thru the five senses. In logic, the process is called induction.
How do you know that boiling an egg for five min utes will make it hard? Or that boiling potatoes for twenty minutes will make them soft and edible? You know it solely because you have tried the experiment, or because you know some one else has. If a cook should boil an egg five minutes and should find it very soft, she would be very much astonished. She would doubtless suspect the accuracy of her clock or of her eyesight, and if the strange event happened fre quently, she might, especially if she were superstitious, think the house bewitched and give notice.
Yet nobody really knows absolutely that boiling an egg five minutes will make its contents hard. All we know is that in the past when eggs were boiled five minutes they did become hard. So we have assumed it to be a law that to boil an egg for that length of time will make it hard.
If a man decides to commit suicide by jumping from a high building, he believes that his body will go to the ground and not up toward the clouds. Yet he does not absolutely know that. All he really knows is that in the past when a man has sprung from a height his body has gone down, not up.
All of our knowledge of the external world is of this sort, namely, inductive, for it is based upon ex perience. We assume that the laws of nature will not change, and that things today will happen as they did yesterday if all conditions are the same.
If for several years a farmer applies nitrates and phosphates to one field and not to another, and uni formly gets a better crop off the first field than off the other, he concludes that these chemicals are good fer tilizers and that he will get a larger crop if he uses them than if be does not.
We observe that immoderate consumers of alco holic beverages frequently get red noses and watery eyes. If we meet a stranger with a red nose and wat ery eyes, involuntarily we conclude that he is an al coholic.
If you examine these illustrations, you will find that in every instance a general conclusion or inference has been reached which has for its basis a number of ob servations or experiences. The fact that boiling an
egg five minutes has always made it bard, leads us to the general conclusion that such will always be the case. That method of arriving at knowledge is called induction, a reasoning from particulars up to the gen eral.
16. hzduction and deduction work together.—Most of our knowledge is obtained by the combined use of induction and deduction. The two methods, so to speak, pull together like a team of horses, one helping the other. Having learned from experience what usually follows the appearance of heavy black clouds, thunder and lightning, men have drawn the conclusion that these phenomena indicate rain. This is an in duction. If we see the sk-y heavily clouded and bear thunder, we say it is going to rain. This is deduc tion, the major premise of which is: Black clouds and thunder are followed by rain; and the minor pre mise : There are now black clouds and thunder ; hence the conclusion : We shall have rain. So in most of our conclusions with respect to ordinary everyday af fairs. We are constantly drawing conclusions in which both induction and deduction are employed. In this rain illustration we get our general proposi tion with regard to the sequence of thunder and rain thru induction, but we reach our particular conclu sion by deduction.
Let us take another illustration. A man is brought into court accused of being a sneak thief. The magis trate has had experience with sneak thieves, let us suppose, and has observed that their lips are usually thin, that their eyes are close together, and that they will not look at you steadily. By induction he has come to the conclusion that men possessing these traits are inclined to thievery. He notes that the prisoner at the bar has all these traits and by deduction he is prejudiced against him. Unconsciously his mind works out this syllogism: Alen of thin lips and fur tive, narrow eyes are sneak thieves; the prisoner has thin lips and furtive, narrow eyes ; therefore, he is a sneak thief. You will say that the magistrate is prejudiced, and that he ought not to let his mind be in fluenced in the way I have indicated, but he cannot help it. As an honest judge, he will do his best to weigh in the balance the evidence for and against the prisoner, but back of all the evidence there will be that ‘`sub-conscious" judgment, and it will not work to the prisoner's advantage.