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EXERCISE LI.

DEDUCTIVE REASONING (CONTINUED).

Subjects :
Fallacies of Democracy. The Malthusian Doctrine.

Mistakes of Epicurus.

Let us consider some methods of overthrowing arguments founded on deductive reasoning. We have already noticed that there are two possibilities of error because the conclusion must be drawn from two premises either one of which may be wrong. The premises therefore need close scrutiny first of all. But there is still a third possibility of error, even granting that the premises are correct: an unwarrantable conclusion may be drawn. We said that the deductive process is an absolutely correct one. So it is. So are many mathematical processes — the process for instance by which we extract the cube root of numbers. But nevertheless we sometimes make mistakes in following out the process and so arrive at incorrect results. In many a deductive argument, if we go over it carefully, we shall find that there has been a mistake in the process. Suppose we say

All wood is ignitible ;
Hickory is ignitible ;

Therefore hickory is wood.

Are the premises correct? Yes. Is the conclusion correct? Yes. But is the process, the deduction,

correct? No. The conclusion therefore is unwarranted and not to be depended upon. As a statement it may chance to be correct (as in this instance), but it is not a correct conclusion to draw, for by the same process a very incorrect conclusion may be arrived at, thus :

All wood is ignitible ;
Gas is ignitible ;

Therefore gas is wood.

The difficulty is that we have not denied that other things besides wood may also be ignitible. We have said nothirg whatever about all ignitible things and therefore we are not warranted in saying anything whatever about any one of them. We have, however, said something about all woods, and we can therefore draw a conclusion about any particular wood, thus :

All wood is ignitible ;
Hickory is wood;

Therefore hickory is ignitible.

And this will be found correct in every particular.

Examine the following arguments for fallacies, and if possible make correct syllogisms of them :

Induction is a process of reasoning ;
Induction furnishes us with knowledge ;

Therefore processes of reasoning furnish us with knowledge.

Induction is the only process of reasoning that furnishes us with knowledge ;

Therefore, all our knowledge is due to induction.

All liquids are vaporizable;
Gold is not a liquid;

Therefore gold is not vaporizable.

Nothing is better than wisdom :
Bread is better than nothing ;

Therefore, bread is better than wisdom.

It is no part of our work here to examine the various fallacies of reasoning and distinguish them and give them names. That belongs to logic. It must suffice for us to recognize the fact that they exist in many disguises, and to be on our guard against them, both in ourselves and in others. After all, they invariably do violence to the axiomatic truths which lie at the foundation of all reason, and every man's "common sense? will generally be sufficient to detect them.

In this exercise our object again is rather destructive — to expose the fallacy of an argument that involves false deduction. It may be as good practice as any to attempt to overthrow some of the arguments advanced on subjects in the last exercise, to show that John Brown was not a hero, or that slavery is an institution to be upheld. These are questions with two sides, and it may well be that fallacies can be detected in the arguments advanced on one side. Or take one of the other subjects. Suppose it has been represented that the era of peace supervening after the crisis of some great political or religious strife fosters the development of literary genius ; that the age of Queen Elizabeth was such an an era in the national history of England ; that Shakespeare lived in that age; that his genius was of the highest order ; that the genius of Shakespeare was therefore the product of his time. If this argument is closely examined it will be found fallacious in several points.

EXERCISE LII.

EVIDENCE.

Subjects : The Character of Columbus. Was the Assassinator of President Garfield Insane? Evidence for or against a Belief in Rhabdomancy ; Spiritualism;

Conservation of Energy; Inoculation for Disease.

Evidence is a general name for everything that is adduced to corroborate a fact or support a thesis. It may be material objects, such as are often exhibited in trials before courts of law. It may be oral or written testimony of witnesses. It may be a combination of circumstances that seem to admit of only one explanation. It may be an expression of opinion by some one who is an expert in the matter under discussion and whose words therefore carry weight. All of these may be elaborated into an argument which may be deemed by the hearer or reader to establish conclusive proof. But the evidence in itself is not necessarily proof.

Each of these kinds of evidence will have a different force and validity, which must be taken into account. For instance, what is called in law “circumstantial evidence” may be exceedingly strong and convincing, and yet many a conclusion drawn from it has afterward been found wrong. The value of verbal testimony depends very much on the intelligence, moral character, and disinterestedness of the witness who offers it. Authority, or the judgment of experts in matters of opinion, will vary greatly in value.

Take the matter of testimony. What can be better than the truthful testimony of an unprejudiced eyewitness? And yet our eyes, and all our senses, are continually deceiving us. A child riding on a train fancies that the fences are flying past him ; a man of wide experience and matured judgment often finds it difficult to determine whether or not a train is moving, past which he is being carried on another train. Clouds seem to be moving in opposite directions when in reality one stratum is simply moving faster than another in the same direction. An object is blue, green, or even red, to different people. The same man is described by one person as tall, by another as of medium stature ; one says his eyes are black, another that they are brown. And all of these witnesses may, feel confident that they are telling the truth. Evidence, we repeat, even the best of evidence, is not proof. Hence the necessity of bringing to bear every scrap of evidence obtainable. The weaving of it into a strong mesh of proof exercises the highest skill of the philosopher, the historian, the scientific demonstrator, the legal advocate. In short, it is the utilization of all the resources of argument.

It will be noticed that the subjects offered thus far have often been put in the form of questions. There are several good reasons for this. The reader will understand at once that the paper is to be argumentative and that the question is an unsettled one in the minds of many people. The interrogative form, too, seems to promise greater fairness of treatment on the writer's part. His answer may be an unqualified Yes or No, but he assumes to start at least from a neutral standpoint and with a spirit of sincere inquiry. The result

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