LESSON XXXVI. REASONING. (Continued.) Difference between Inductive and Deductive Reasoning.—We saw in the last lesson that the difference between deductive and inductive reasoning is rather a difference in the method of proving conclusions already inferred than a difference in the method of inferring them; that when we appeal to a universal proposition to prove our conclusion, the reasoning is called deductive; inductive when we appeal to one or more particular propositions. Why does the same Method of Reasoning sometimes Lead to a True, and sometimes to a False Conclusion? But how is that I am able to find the proof of a fact in particular propositions? When you say, "I know that this is a Maréchal Niel because I know that all the roses that have the characteristics of this rose are Maréchal Niels," if I disagree with you it is because I do not believe your premise. Admitting your premise, that all the roses that have the characteristics of this rose are Maréchal Niels, I must admit your conclusion. But when the child argues, "Sugar is white, snow is white, therefore snow is sugar," I admit his premises, but deny his conclusion. But when he argues, "This and that and the other unsupported bodies have fallen; this stone is an unsupported body, therefore it will fall," I admit the truth of his conclusion. In both cases he argues from true particular propositions. We have to inquire (1) how he came to choose those particulars in order to prove his conclusion; and (2) how it happened that apparently the same method led, in one case, to a false conclusion; in the other, to a true one. We Base Affirmative Conclusions on Likenesses, but never on Differences. I think we shall see how to answer the first question if we ask ourselves if a child can believe that snow is sugar because the one is white and the other sweet. We know that he can not. We know that children-human beings in general-reason from observed likenesses to unobserved likenesses, but never from differences to affirmative conclusions. We know that the child argued that snow is sugar because snow and sugar resemble each other in being white - because they belong to the class of white objects. The proof, in a word, that snow is sugar he found in the fact that both are white. He took one white thing- sugar to be the type of all white things-judged implicitly that all white things are sugar. He argued, then, that snow is sugar because it is one of the class of white things, all of which are sugar. He selects the particular propositions, This unsupported object has fallen, That unsupported object has fallen, etc., to prove that the stone will fall if it is unsupported, for the same reason. Can he believe that a stone will fall because a robin flies, and a geranium bears blossoms, and a maple puts forth leaves in spring-time? Certainly not. These facts and the one he believes do not resemble each LIKENESSES, BUT NOT DIFFERENCES. 331 other are not members of a class. He believes that an unsupported stone will fall, on the ground that this and that and the other body have done so, because he takes this, that, and the other body as types of the class. He has made a class of unsupported bodies, and has judged that those he has observed are examples of the entire class. When, then, he reasons that the stone will fall if unsupported, because this and that and the other body have done so, he really reasons that it will do so because all unsupported bodies will do so. We see, then, that there is no essential difference between inductive and deductive reasoning. When I prove a particular fact by other particular facts, I do so because they are members of the same class as the one about which I am trying to prove something, and because I have already, explicitly or implicitly, reached a conclusion about the entire class. When a universal judgment is consciously appealed to, the reasoning is deductive; when it is unconsciously appealed to, it is said to be inductive; and that is the sole difference between deductive and inductive reasoning. I say, "I am going to die sometime." You ask, "Why?" "Because all men are mortal." There I appeal consciously to a universal proposition. If I reply, "Because this and that and the other man have died," I certainly appeal, perhaps unconsciously, to a universal proposition, since it is only because this and that and the other individual and I are members of the same class that what has happened to them throws any light on what is likely to happen. to me. We see, then, that we appeal to certain particular propositions to prove a fact, because they are included in a universal judgment that we have made. All Inductive Reasoning is Deductive Reasoning. Now, we see why the same kind of reasoning sometimes leads to a true conclusion and sometimes to one that is false. All inductive reasoning is deductive reasoning. When the universal implied by the particulars is false, the conclusion based upon it will be false. All white things are not sugar. Hence it is a mistake to say that snow is sugar because it is white. All unsupported bodies will fall. Hence I am justified in concluding that this stone will, because this and that and the other bodies have done so when I take them to be types of the class. The proof in deductive reasoning may always be thrown into the following form called a syllogism : (Major premise.) All white things are sugar; (Minor premise.) Snow is a white thing; Therefore, snow is sugar. Why Able Men so often Differ. We see here very plainly again that an act of reasoning may be altogether correct as a process, and yet lead to a false conclusion, because one of the premises is incorrect. That enables us to see why able men so often differ with each other; they start from different premises. Take the great differences you find between men in matters of politics, scienceevery department of thought- and you will often find that they rest at bottom on the fact that those who differ started from different major premises. A physicist or physiologist, for example, is very likely to believe that nothing can cause a change in matter but matter. If so, he is almost certain to be a materialist, since the changes in the body that we usually attribute to consciousness, he will attribute to the brain, His reasoning may be thrown WHY ABLE MEN SO OFTEN DIFFER. 333 into the form of a syllogism: Nothing can cause a change in matter but matter. But consciousness is not matter. Therefore, consciousness can not cause a change in the body. A psychologist, on the other hand, may assume that nothing can have the characteristics that the mind has without having some of the attributes of a substance. If so, he will not be a materialist. His reasoning may be thrown into the following syllogism: Nothing can have such characteristics as the mind has without being a substance. But the mind can not be a substance if mental facts are mere phenomena of the brain. Therefore mental facts are not mere phenomena of the brain. One man says, "All measures that tend to promote home production are beneficial. A protective tariff does this; therefore a protective tariff is beneficial." Another says, "Undoubtedly your conclusion is true if your major premise is, but I deny your major premise. I hold that what promotes the interests of individuals promotes the interests of nations." Here we have an argument leading to a conclusion that directly contradicts the first, because it starts from a major premise that contradicts the major premise of the first argument. Compare the argument of ExSpeaker Reed in the North American Review, January, 1890, with the reply of Senator Carlisle the former defending the rules of the House of Representatives that had just been adopted by the Republican majority, the latter severely criticising them. Reed reasons substantially as follows: Whatever rules are necessary to enable the House to transact business are wise; the rules adopted by the Republicans are necessary to enable the House to transact business; therefore they are wise. Carlisle, on the other hand, reasons substantially as follows: Whatever |