Practical Argumentation · Chapter 10A. Tests of the Source of Evidence
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Since in courts of law, in college debate, and in all kinds of argumentation, facts are established by the testimony of witnesses, the sources of evidence are the witnesses who give it. The debater and the argumentative writer have not the opportunity, as has the lawyer, of producing the witnesses and permitting them to tell their own stories to the audience. He must himself relate the evidence; and, in order that it may be believed, he must tell whence it comes. The sources of evidence may be common rumor, newspapers, magazines, official documents, private citizens, or public officials. The extent to which these witnesses are accepted as trustworthy by the people before whom they are quoted determines in a large measure whether or not the evidence will be believed. Tests for determining the trustworthiness of witnesses will next be given.
The first test of the source of evidence should be:—
(1) Is the witness competent to give a trustworthy account of the matter under consideration?
To answer this question, first determine whether the facts to be established are such that any ordinary person can speak concerning them with reasonable accuracy, or whether they can be understood only by persons who have received special training. A landsman could well testify that a naval battle had occurred, but only a man with nautical training could accurately describe the maneuvers of the ships and tell just how the engagement progressed. A coal heaver's description of a surgical operation would establish nothing, except perhaps the identity of the people and a few other general matters; only a person with a medical education could accurately describe the procedure. The testimony of any one but a naturalist would not even tend to prove the existence of an hitherto unknown species of animal life. A witness without technical knowledge cannot give reliable evidence on matters of a technical nature.
Then, if it is found that the witness does possess the necessary technical training, or that no previous training is necessary, still further test his ability to give reliable evidence by asking whether he has had ample opportunity for investigating the facts to the existence of which he testifies. For even a skilled player sitting in the first base bleachers at a baseball game to criticise an umpire's decisions on balls and strikes is absurd; the opinion of a transient visitor to Panama on the methods used in digging the canal is not valuable; a traveler who has spent a single month in Japan cannot draw reliable conclusions on the merits and defects of its political structure. In not one of these cases has the opportunity for investigation been sufficient to render the witness able to give reliable evidence.
A current magazine in discussing the weakness of testimony that comes from incompetent witnesses says:—
Generalizations about the tastes and interests of the age are so easy that all except the most wary fall into them, and the world is full of off-hand opinions touching the condition of society and the state of the world, which are far more conspicuous for courage than for discretion. There are very few men or women in any particular period who know it intimately enough, and with sufficient insight and sympathy, to pass judgment upon it. One hears almost every day sweeping judgments about Americans, English, French, Germans, Chinese, and Japanese which are entirely valueless, unless they are based on a very broad and intimate knowledge of these various peoples, a knowledge which, in the nature of things, few people possess. The charming American girl who declared that, since gloves are cheaper in Paris, American civilization is a failure, may stand for a type of interesting and piquant oracles, to be heard with attention, but under no circumstances to be followed. Americans are so familiar with the European traveler who arrives and makes up his opinion over night in regard to men, morals, and manners in the Western world and have so often been the victim of this self-confident critic, that they ought not to repeat the same blunder in dealing with other peoples. [Footnote: The Outlook, July 20, 1907.]
In the court room, where witnesses are present and can be carefully examined by the lawyers on both sides, it is customary to apply both mental and physical tests. The witness who testifies to knowledge of some event that occurred a long time before is given a memory test; the senses, also, through which occurrences are perceived are frequently examined. But as writers and debaters in general seldom have the opportunity to apply tests of this sort to their sources of information, and as these tests are seldom important outside of the law courts, they are not taken up in detail in this book.
The second test of the source of evidence should be:—
(2) Is the witness willing to give an accurate account of the matter?
One important influence that may cause a witness to give false evidence is self-interest. Not only individuals, but social and industrial organizations, political parties, communities, and states are frequently swayed by this emotion to the extent of deliberately perverting the truth. The evidence found in newspapers and other publications is often false, or at least misleading, because it has been tampered with by those who put their selfish interests before all else. The owner of an industry protected by a high tariff would scarcely be considered a reliable witness in matters affecting tariff reform. The opinion of a railroad magnate on the subject of a compulsory two-cent rate law would not be considered as unbiased. No disinterested seeker after truth would accept the political conclusions of a newspaper owned by a politician or recognized as the organ of a certain party. In all such cases, self-interest may prompt the witness to make statements not in strict accordance with the truth. Perjury in the court room is not uncommon; falsehood elsewhere must be guarded against. The arguer should always carefully scrutinize the testimony of a witness that has any special interest in the matter for which evidence is being sought. Though the self-interest is strong, the witness may be willing to state the matter accurately; but, as long as human nature remains as it is, this willingness should not be taken for granted.
The third test of the source of evidence should be:—
(3) Is the witness prejudiced?
Another emotion that frequently keeps a witness from telling the exact truth is prejudice. Every one is familiar with instances of how this passion warps men's morals and corrupts their judgment. If a man is prejudiced for or against a person or a system, he cannot be accepted as a trustworthy witness in matters where his prejudice comes into play. Should an economist known to favor socialism write a treatise advocating municipal ownership of public utilities, his evidence and his reasoning would not be convincing; it would be taken for granted that he looked at the subject through socialistic spectacles. A person who sets out with the expectation and intention of finding flaws in anything usually succeeds. Though he is willing to tell the exact truth, yet because of his prejudice he is sure to see only that which will coincide with his preconceived opinions. For this reason, political speeches and intensely partisan books and papers are invariably unreliable sources of evidence even though they are not intentionally dishonest.
The fourth test of the source of evidence is:—
(4) Does the witness have a good reputation for honesty and accuracy?
The human conscience is so constituted that many people deviate from the truth for no apparent reason whatever. Some are given to exaggeration; some habitually pretend to know that of which they are entirely ignorant; others are so inaccurate that everything they say is open to grave suspicion. If a witness is known to have been repeatedly dishonest or inaccurate in the past, little reliance should be placed in his testimony. "Yellow journalism," which is largely the reflection of common rumor, affords constant examples of witnesses that give questionable evidence.
Ability and willingness to give exact evidence, an unprejudiced attitude, and a good reputation for honesty and accuracy are the qualities that should characterize the sources of evidence. If a writer or speaker is securing testimony from friends or acquaintances, the application of these tests is not difficult. If, however, the sources are books and periodicals, his work is harder; but to be successful, he must not shirk it. When one procures evidence from books, he should investigate the character and standing of the author. When one obtains it from signed articles in papers and magazines, he must consider both the author and the character of the publication. In the case of newspaper "stories" and editorials, one should find out on what general policy and principles the paper is conducted. A cautious arguer will always avoid, as far as he can, the use of evidence that comes from a doubtful source. If one finds that an opponent has used the testimony of questionable witnesses, he can, by exposing the fact, easily refute the argument.
NECESSITY OF STATING SOURCES. It sometimes happens that an arguer fails to state the source of his evidence. This omission is usually fatal to success. No one is likely to put much confidence in statements that are introduced by such flimsy preambles as, "A certain statesman has declared"; "I have read somewhere"; "An acquaintance told me." Not only must evidence come from sources that seem good to the writer, but those sources must be satisfactory to the audience. In the last analysis the audience is the judge of what is credible and what is not. Moreover, if the evidence is of great importance, or is liable to be disputed, the arguer should show in a few words why the witness is especially reliable.