Thus, in the following statements, the truth of one proposition leads to the belief that the other is also true:--

_a._ Henry has studied hard this year; therefore he will pa.s.s his college entrance examinations.

_b._ The man has severed an artery; therefore he will probably bleed to death before the physician arrives.

_c._ It will soon grow warmer, because the sun has risen.

_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 a.s.sume that there has been a cause, and we direct our argument to proving what it is. An effect is so a.s.sociated 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 a.s.sociated 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 princ.i.p.al 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 circ.u.mstances might point to some one cause and so lead you to a.s.sume that it was the one.

Under _arguments from sign_ should be included also those cases when we pa.s.s 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 pa.s.s directly from one effect to another.

As used by rhetoricians, arguments from sign include also arguments from attendant circ.u.mstances. 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 pa.s.s 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 circ.u.mstance, 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 cla.s.s. In dealing with objects of the physical world, if essential and invariable qualities of the object are considered, they may be a.s.serted to be qualities of each member of the cla.s.s, and such an argument from an individual to all the members of the cla.s.s 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 circ.u.mstances 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 a.n.a.logy.+--a.n.a.logy is very much relied upon in practical life. Reasoning from a.n.a.logy 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 a.n.a.logy that Mars must also, be inhabited.

An a.n.a.logy is seldom conclusive and, though it is often effective in argument, it must not be taken as proof of fact. The mind very readily observes likenesses, and when directed toward the establishing of a proposition easily overlooks the differences. In order to determine the strength of an argument from a.n.a.logy, attention should be given to the differences existing between the two propositions considered. False a.n.a.logies are very common. We must guard against using them, and especially against allowing ourselves to be convinced by them. Even when the resemblance is so slight as to render a.n.a.logy impossible, it may serve to produce a metaphor that often has the effect of argument.

It is much easier to captivate the fancy with a pretty or striking figure than to move the judgment with sound reason.... His (the speaker's) picture appeals to the mind's visible sense, hence his power over us, though his a.n.a.logies are more apt to be false than true....

The use of metaphor, comparison, a.n.a.logy, is twofold--to enliven and to convince; to ill.u.s.trate and enforce an accepted truth, and to press home and clinch one in dispute. An apt figure may put a new face upon an old and much worn truism, and a vital a.n.a.logy may reach and move the reason.

Thus when Renan, referring to the decay of the old religious beliefs, says that the people are no poorer for being robbed of false bank notes and bogus shares, his comparison has a logical validity....

The accidental a.n.a.logies or likenesses are limitless, and are the great stock in trade of most writers and speakers. An ingenious mind finds types everywhere, but real a.n.a.logies are not so common. The likeness of one thing to another may be valid and real, but the likeness of a thought with a thing is often merely fanciful....

I recently have met with the same fallacy in a leading article in one of the magazines. "The fact revealed by the spectroscope," says the writer, "that the physical elements of the earth exist also in the stars, supports the faith that a moral nature like our own inhabits the universe." A tremendous leap--a leap from the physical to the moral. We know that these earth elements are found in the stars by actual observation and experience; but a moral nature like our own--this is a.s.sumed, and is not supported by the a.n.a.logy.

John Burroughs: _a.n.a.logy, True and False_.

Notice the use of a.n.a.logy in the argument below.

There is only one cure for the evils which newly acquired freedom produces; and that cure is freedom. When a prisoner first leaves his cell he cannot bear the light of day: he is unable to discriminate colors, or recognize faces. But the remedy is, not to remand him into his dungeon, but to accustom him to the rays of the sun. The blaze of truth and liberty may at first dazzle and bewilder nations which have become blind in the house of bondage. But, let them gaze on, and they will soon be able to bear it. In a few years men learn to reason. The extreme violence of opinions subsides. Hostile theories correct each other. The scattered elements of truth cease to contend and begin to coalesce, and at length a system of justice and order is educed out of the chaos.

--Macaulay: _Milton_.

+193. Summary of Arrangement.+--The necessity of argument arises because some one does not believe the truth of a proposition. To establish in his mind a belief, we must present our arguments in an orderly and convincing way. The order will usually be to show him first the possibility and then the probability, and finally to lead him as near to certainty as we can.

We may say, therefore, that we should use arguments from cause, arguments from sign, and arguments from example in the order named.

Another principle of arrangement is that inductive argument will usually precede deductive argument. We naturally proceed by induction to establish general truths which, when established, we may apply. If our audience already believe the general theories, the inductive part may be omitted.

Both of these principles of arrangement should be considered with reference to that of a third, namely, climax. Climax means nothing more than the orderly progression of our argument to the point where it convinces our hearer. We call that argument which finally convinces him the strongest, and naturally this should be the end of the argument. Of several proofs of equal grade, one that will attract the attention of the hearer should come first, while the most convincing one should come last.

In arranging arguments attention needs also to be given to coherence. One proof may be so related to another that the presentation of one naturally suggests the other. Sometimes, for the sake of climax, the coherent order must be abandoned. More often the climax is made more effective by following the order which gives the greatest coherence.

+Theme CII.+--_Prove one of the following propositions:_

1. The Presidential term should be extended.

2. Bookkeeping is of greater practical value than any other high school study.

3. In cities all buildings should be restricted to three stories in height.

4. Sumptuary laws are never desirable.

5. No pupil should carry more than four studies.

6. This school should have a debating society.

(Have you proved possibility, probability, or actuality? Have you used arguments from cause, sign, or example? Consider the arrangement of your arguments. Consider the a.n.a.logies you have used, if any. Can you shorten your theme without weakening it?)

+194. The Brief.+--Arrangement is of very great importance in argument. In fact, it is so important that much more care and attention needs to be given to the outline in argument, and the outline itself may be more definitely known to the hearer than in the other forms of discourse. In description and narration especially, it detracts from the value of the impressions if the reader becomes aware of the plan of composition. In exposition a view of the framework may not hinder clear understanding, but in argument it may be of distinct advantage to have the orderly arrangements of our arguments definitely known to him whom we seek to convince.

The brief not only a.s.sists us in making our own thought orderly and exact, but enables us to exclude that which is trivial or untrue. An explanation may fail to make every point clear and yet retain some valuable elements, but an argument fails of its purpose if it does not establish a belief. A single false argument or even a trivial one may so appeal to a mind prejudiced against the proposition that all the valid proofs fail to convince. This single weakness is at once used by our opponent to show that our other arguments are false because this one is. A committee once endeavored to persuade the governor of a state not to sign a certain bill, but they defeated themselves because their opponents pointed out to the governor that two of the ten reasons which they presented were false and that the committee presenting them knew they were false. This cast a doubt upon the honesty of the committee and the validity of their whole argument, and the governor signed the bill.

The brief differs from the ordinary outline in that it is composed of complete sentences rather than of topics.

Notice the following example.

+Term examinations should be abolished.+

AFFIRMATIVE