(a) Hurtful admissions constitute an especially valuable kind of evidence. Since men are not wont to give evidence detrimental to their personal interest unless impelled to do so by conscientious scruples, any testimony damaging to the one who gives it is in all probability not only truthful, but also the result of careful investigation. When a practising physician admits that half the ailments of mankind are imaginary or so trivial as to need no medical attention, he is making a statement that is likely to injure his business; for this reason he is probably stating the result of his experience truthfully. If a railroad president says that in his opinion government supervision of railroads will benefit the public in the matter of rates and service, it may be taken for granted that he has given his honest belief, and that his natural reluctance to surrender any authority of his own has kept him from speaking carelessly. If a member of the United States Senate admits that that body is corrupt, and selfish, and untrustworthy, he is lowering his own rank; therefore it is reasonable to believe that he is speaking the truth according to his honest belief.
The following is an example of this kind of evidence:—
It was stated during the Manchurian campaign that the Jewish soldiers, of whom Kuropatkin had about 35,000, not only failed to hold their ground under fire, but by their timidity threw their comrades into panic. But good evidence can be cited from the correspondents of the Novoye Vremya, an Anti-Semitic organ, to the effect that among the Jews were found many "intrepid and intelligent soldiers," and that a number of them were awarded the St. George's cross for gallantry. [Footnote: The Nation, June 11, 1908.]
It is hardly necessary to add that one who places especial reliance on this kind of evidence must be sure that the admission is really and not merely apparently contrary to the interest of the one who gives it.
(b) Another particularly valuable kind of evidence is negative evidence, or the evidence of silence. Whenever a witness fails to mention an event which, if it had occurred, would have been of such interest to him that he might reasonably have been expected to have mentioned it, his silence upon the matter becomes negative evidence that the event did not occur. For many years no one suggested that Bacon wrote the Shakespearean plays; this absence of testimony to the belief that Bacon wrote them is strong evidence that such belief did not exist until recently, a fact that tends to discredit the Baconian theory of authorship. The fact that in the writings of Dickens and Thackeray no mention is made of the bicycle is negative evidence that the bicycle had not then come into use. That Moses nowhere in his writings speaks of life after death is negative evidence that the Hebrews did not believe in the immortality of the soul. If admittedly capable and impartial officials do not inflict penalties for foul playing during a football game, there is strong presumption that little or no foul playing occurred.
The following paragraph, taken from a current magazine, shows how this kind of evidence may be handled very effectively:—
A sharp controversy has been raging in the European press over the question whether Gambetta secretly visited Bismarck in 1878. Francis Laur, Gambetta's literary executor, has published an article asserting that he did, and giving details (rather vague, it must be admitted) of the conversation between the two statesmen. But he offers not a scrap of documentary proof. He is not even sure whether the interview took place at Friedrichsruh or at Varzin. This is rather disconcerting, especially in view of the fact that Bismarck never made the slightest reference in his reminiscences or letters to the visit of Gambetta, if it occurred, and that the minute Busch never mentioned it. [Footnote: The Nation, September 5, 1907]
ARGUMENT FROM AUTHORITY.
There is a particular kind of evidence frequently available for debaters and argumentative writers known as argument from authority. This evidence consists of the opinions and decisions of men who are recognized, to some extent at least, as authorities on the subjects of which they speak. An eminent scientist might explain with unquestioned certainty the operation of certain natural phenomena. A business man of wide experience and with well recognized insight into national conditions might speak authoritatively on the causes of business depressions. In religious matters the Bible is the highest authority for orthodox Christians; the Koran, for Mohammedans. In legal affairs the highest authorities are court decisions, opinions of eminent jurists, and the Constitution. If a certain college president is considered an authority in the matter of college discipline, then a quotation from him on the evils of hazing becomes valuable evidence for the affirmative of the proposition, "Hazing should be abolished in all colleges." If the arguer wishes to strengthen his evidence, he may do so by giving the president's reasons for condemning hazing; but he then departs from pure argument from authority. Pure argument from authority does not consist of a statement of the reasons involved; it asserts that something is true because some one who is acknowledged to be an authority on that subject says it is true.
Argument from authority differs from other evidence in that it involves not merely investigation but also the exercise of a high degree of judgment. The statement that in 1902, in the United Kingdom, two hundred and ninety-five communities of from 8,000 to 25,000 inhabitants were without street-car lines is not argument from authority; the discovery of this truth involved merely investigation. On the other hand, if some reputable statesman or business man should say that street-car facilities in the United States excelled those of England, this evidence would be argument from authority; only through both investigation and judgment could such a statement be evolved.