Definition of Terms. The first error arises from a misunderstanding of terms. It is often said that George Eliot is a poet; there are some who disagree. Certain it is that she wrote in verse form; and it is true that she has embodied noble thoughts in verse; but it is quite as true that she lacks “the bird-note.” If this were reduced to a syllogism, it would not be a discussion of whether George Eliot be a poet, but rather a discussion of what is a poet. Stated, it reads: All persons who embody noble thoughts in verse form are poets. George Eliot is a person who has embodied noble thoughts in verse form. Therefore George Eliot is a poet. If the major premise of this syllogism be granted, the conclusion is unquestionable. The terms should be defined at the beginning; then this error, springing from a misunderstanding of terms, perhaps the most common, would be avoided.
Undistributed Middle. [131] The second error arises from the fact that the middle term is not “distributed;” that is, the major premise makes no statement about all the members of a class. The premises in the following are true, but the conclusion is nonsense.
A horse is an animal.
Man is an animal.
Therefore, man is a horse.
The middle term, in this case “animal,” must be “distributed;” some statement must be made of all animals. The following would be true: All animals have life; therefore man has life. The major premise predicates life of all animals.
False Premises. A third error in a syllogism is in the premises themselves. If either premise be false, the conclusion is not necessarily true. A parent might say to his son, “You are doing wrong, and you will pay the penalty for it soon.” Generally he would be right. However, if this were put into a syllogism, it would read as follows: All persons who do wrong pay the penalty soon. You are such a person. Therefore, etc. Admitting the son is breaking the law, the fact is that the major premise is not always true, and the conclusion holds the weakness of the weak premise. Again, supposing everybody accepted the general truth, “All unrepentant sinners will be punished.” The minister might then say to a young man, “You will certainly be punished, because all unrepentant sinners will be punished.” The young man might deny the suppressed minor premise, which is, “You are an unrepentant sinner.” Both premises must be true if they prove anything. The conclusion contains the weakness of either premise. In both of these examples note that the mistake is in the premise which does not appear. In an enthymeme, great care [132] should be taken with the suppressed premise. Be sure it is true when you use this form of argument, and be sure to look for it and state it in full when examining another’s argument. It is a common way of hiding a weak point to cover it in the suppressed premise of an enthymeme.
Method of Induction. Induction, which proceeds directly opposite to the method of deduction, is the method by which all our ultimate knowledge has been obtained. By observing individual instances man has gathered a great store of general truths. There was a time when the first man would not have been justified in saying, “The sun will rise in the east to-morrow.” The general law had not been established. To-day it is practically certain that the sun will rise in the east to-morrow morning, because it has done so for thousands of years; the large number of instances establishes the general truth. Yet there may come a day when it will rise in the south, or not rise at all. Until every case has been tried and found to conform to the law, theoretically man cannot be absolutely certain of any general truth. There may come an exception to the general rule that all men must die. So far, however, there is no experience to justify any man in hoping to escape death. “As sure as death” means in practice absolutely sure, though this is not what is called a perfect induction; that is, an induction in which every possible case has been included. “All the other States are smaller than Texas” is a perfect induction, but it forms no basis for argument. All the cases must be known for a perfect induction; there is no unknown to argue to. This, then, is only a short statement of many individual truths, and has but little of value. Induction that is imperfect is more valuable; for with many cases the probability becomes so strong that it is a practical certainty. It is the method of science.
[133] More valuable for literature is another division of arguments into arguments from cause, arguments from sign, and arguments from example.
Arguments from Cause. Arguments from cause include those propositions which, if they were granted, would account for the fact or proposition maintained. The decisive test is to suppose the proposition to be true; then, if it will account for the condition, it is an argument from cause. A child holds its finger in a flame; therefore its finger is burned. If the first proposition be supposed to be true, it will account for a burned finger. It is an argument from cause, and it is conclusive. Again, if a man severs his carotid artery, he will die. If the first proposition be supposed to be true, it will account for the man’s subsequent death. Now, supposing a man takes strychnine, he will die. This is not quite so sure. If a stomach-pump were used or an antidote given, he might not die. The cause has been hindered in its action, or another cause has intervened to counterbalance the first. If, then, a cause be adequate to produce the effect, and if it act unhindered or unmodified, the effect will certainly follow the active cause. An argument that uses as a premise such a cause may predicate its effect as a conclusion with absolute certainty. Such an argument is conclusive.
The argument from cause is used more frequently to establish a probability than to prove a fact or proposition. However strong the proofs of a statement may be, men hesitate to accept either the statement or the proofs if the proposition is not plausible, or, as people say, if “they do not understand it,” or if “it is not reasonable.” If a murder be done and circumstances all point to your friend, you do not believe your friend to be the criminal until some fact is produced [134] sufficient to cause your friend to commit the crime,—until some motive is established. If it be shown that the friend hated the murdered man and would be benefited by his death, a motive is established,—the proposition is made plausible. A man could “understand how he came to do it.” The hatred and the benefit being granted, they would account for his deed. It is an argument from cause, used not as a proof, but to establish a probability. It makes the proposition ready for proof.
Arguments from Sign. The second class of arguments, arguments from sign, is most often used for proof. If two facts or conditions always occur together, the presence of one is a sign of the presence of the other. Cause and effect are so related that if either be observed, it is an indication of the other. No cause acts without a consequent effect; an effect is a sure sign of a preceding cause. Supposing one should say, “Because the flowers are dead, there was a frost,” or “If ice has formed on the river, it must have been cold,” in both instances the argument would be an argument from sign. Both also proceed from the effect to the cause. Only a low temperature forms ice on the river; the argument from effect to cause is conclusive. In the first case, the argument is not conclusive, because flowers may die from other causes. In a case like this, it is necessary to find all possible causes, and then by testing each in succession to determine which could not have acted and leave the one that is the only actual cause. A man is found dead; death has resulted from natural causes, from murder, or from suicide. Each possible cause would be tested; and by elimination of the other possible causes the one right cause would be left. This method of elimination is frequently employed in arguments from effect to cause. [135] When this method is used the alternatives should be few, else it gives rise to confusion and to lack of attention caused by the tediousness of the discussion. And an enumeration of all possible causes must be made; for if one be omitted it may be the one that is in fact the right one.