Composition-Rhetoric

by Stratton D. Brooks; Marietta Hubbard

An argument from cause may be of itself conclusive evidence of the fact. But, for the most part, such arguments merely establish the possibility or probability of the proposition and so render it ready for proof. In our arrangement of material, we therefore place such arguments first.

+190. Argument from Sign.+—Cause and effect are so closely united that when an effect is observed we assume that there has been a cause, and we direct our argument to proving what it is. An effect is so associated with its cause that the existence of an effect is a sign of the existence of a cause, and such an argument is called an argument from sign. Reasoning from sign is very common in our daily life. The wild geese flying south indicate the approach of cold weather. The baby's toys show that the baby has been in the room. A man's hat found beside a rifled safe will convict the man of the crime. A dog's track in the garden is proof that a dog has been there.

If the effect observed is always associated with the same cause, the argument is conclusive. If I observe as an effect that the river has frozen over during the night, I have no doubt that it has been caused by a lowering of the temperature.

If two or three possible causes exist, our argument becomes conclusive only by considering them all and by showing that all but one did not produce the observed effect. If the principal of a school knows that one of three boys broke a window light, he may be able to prove which one did it by finding out the two who did not. If a man is found shot to death, the coroner's jury may prove that he was murdered by showing that he did not commit suicide. If there are many possible causes, the method of elimination becomes too tedious and must be abandoned. If you find that your horse is lame, it would be difficult to prove which of the many possible causes actually operated to produce the lameness, though the attendant circumstances might point to some one cause and so lead you to assume that it was the one.

Under arguments from sign should be included also those cases when we pass directly from one effect to another that arises from the same cause; as, "I hear the windmill turning, it will be a good day to sail;" or, "These beans are thrifty, therefore if I plant potatoes here I shall get a good crop." In these sentences the wind and the fertile soil are not mentioned, but we pass directly from one effect to another.

As used by rhetoricians, arguments from sign include also arguments from attendant circumstances. If we have observed that two events have happened near together in time, we accept the occurrence of one as a sign that the other will follow. When we hear the factory whistle blow, we conclude that in a few minutes the workmen will pass our window on their way home. Such a conclusion is based upon a belief established by an inductive process. The degree of probability that it gives depends upon the number of times that it has been observed to act without failure. If we have seen two boys frequently together, the presence of one is a sign of the probable presence of the other. A camp fire would point to the recent presence of some one who kindled it.

In using an argument from sign care must be taken not to confuse the relation of cause and effect with that of contiguity in time or place. Do not allege that which happened at the same time or near the same place as a cause. If you do use an attendant circumstance, be sure that it adds something to the probability.

+191. Argument from Example.+—It has been pointed out in the study of inductive reasoning (Section 176) that a single example may suffice to establish a general notion of a class. In dealing with objects of the physical world, if essential and invariable qualities of the object are considered, they may be asserted to be qualities of each member of the class, and such an argument from an individual to all the members of the class is convincing. They thus rank with arguments from sign as effective in proving the certainty of a proposition.

In dealing with human actions, on the other hand, examples are seldom proofs of fact. We cannot say that all men will act in a certain way under given circumstances because one man has so acted. Nevertheless, arguments by examples are frequently used and are especially powerful when we wish not only to convince a man, but also to persuade him to action. This persuasion to action must be based on conviction, and in such a case the argument from sign that convinces the man of the truth of a proposition should precede the example that urges him to action. After convincing a friend that there are advantages to be derived from joining a society, we may persuade him to join by naming those who have joined.

+192. Argument from Analogy.+—Analogy is very much relied upon in practical life. Reasoning from analogy depends upon the recognition of similarity in regard to some particulars followed by the inference that the similarity extends to other particulars. As soon as it was known that the atmospheric conditions of the planet Mars are similar to those of the earth, it was argued by analogy that Mars must also, be inhabited.