Reference to our "map" indicates that there might be several other varieties of reasoning, and there are, indeed, though they are scarcely as important as those already mentioned. Reasoning sometimes starts with the observation of P, which means something that might prove useful on some future occasion. Your attention is caught by these prominent words in an advertisement, "$100 a week!" That might come in handy on some future occasion, and you look further to see how all that money can be attached to S, yourself on some future occasion. You soon learn that you have only to secure subscriptions for a certain magazine, [{478}] and that income may be yours. P is the money, and M is the occupation that gives the money, while S is yourself supposedly entering on this occupation and earning the money. This type of reasoning is really quite common. If we see a person making a great success of anything, we try to discover how he does it, reasoning that if we do the same, we shall also be successful; or, if we see some one come to grief, we try to see how it happened, so as to avoid his mistake and so the bad consequences of that mistake. We plan to perform M so as to secure P, or to avoid M in the hope of avoiding P.
Sometimes, not so rarely, we have both premises handed out to us and have only to draw the conclusion. More often, we hear a person drawing a conclusion from only one expressed premise, and try to make out what the missing premise can be. Sometimes this is easy, as when one says, "I like him because he is always cheerful", from which you see that the person speaking must like cheerful persons. But if you hear it said that such a one "cannot be a real thinker, he is so positive in his opinions" or that another "is unfeeling and unsympathetic from lack of a touch of cruelty in his nature", you may have to explore about considerably before finding acceptable major premises from which such conclusions can be deduced.
Finally, in asking what are the qualifications of a good reasoner we can help ourselves once more by reference to the syllogistic map. To reason successfully on a given topic, you need good major premises, good minor premises, and valid conclusions therefrom.
(a) A good stock of major premises is necessary, a good stock of rules and principles acquired in previous experience. Without some knowledge of a subject, you have only vague generalities to draw upon, and your reasoning process will be slow and probably lead only to indefinite conclusions. [{479}] Experience, knowledge, memory are important in reasoning, though they do not by any means guarantee success.
(b) The "detective instinct" for finding the right clues, and rejecting false leads, amounts to the same as sagacity in picking out the useful minor premises. In problem solution, you have to find both of your premises, and often the minor premise is the first to be found and in turn recalls the appropriate major premise. Finding the minor premise is a matter of observation, and if you fail to observe the significant fact about the problem, the really useful major premise may lie dormant, known and retained but not recalled, while false clues suggest inapplicable major premises and give birth to plenty of reasoning but all to no purpose. Some persons with abundant knowledge are ineffective reasoners from lack of a sense for probability. The efficient reasoner must be a good guesser.
(c) The reasoner needs a clear and steady mental eye, in order to see the conclusion that is implicated in the premises. Without this, he falls into confusion and fallacy, or fails, with the premises both before him, to get the conclusion. The "clear and steady mental eye", in less figurative language, means the ability to check hasty responses to either premise alone, or to extraneous features of the situation, so as to insure that "unitary response" to the combination of premises which constitutes the perceptive act of inference.
EXERCISES
1. Outline the chapter.
2. In what respects does the animal's solution of a problem fall short of reasoning?
3. Give a concrete instance of reasoning belonging under each of the types mentioned in the text.
4. How is it that superstitions such as that of Friday being an unlucky day persist? What would be the scientific way of testing such a belief?
5. What causes tend to arouse belief, and what to arouse doubt?
6. Introspective study of the process of thinking. Attempt to solve some of the following problems, and write down what you can observe of the process.
(a) What is it that has four fingers and a thumb, but no flesh or bone?
(b) Why does the full moon rise about sunset?
(c) If a book and a postage stamp together cost $1.02, and the book costs $1.00 more than the stamp, how much does the stamp cost?
(d) A riddle: "Sisters and brothers have I none, yet this man's father is my father's son."
(e) Prove that a ball thrown horizontally over level ground will strike the ground at the same time, no matter how hard it is thrown.
(f) If no prunes are atherogenous, but some bivalves are atherogenous, can you conclude that some prunes are not bivalves?
(g) Deduce, as impersonally as possible, the opinion of you held by some other person.