The most damaging evidence was that of one Allen, who swore that he had seen Armstrong strike Metzker about ten or eleven o'clock in the evening. When asked how he could see, he answered that the moon shone brightly. Under Lincoln's questioning he repeated the statement until it was impossible that the jury should forget it. With Allen's testimony unimpeached, conviction seemed certain.
Lincoln's address to the jury was full of pathos. It was not as a hired attorney that he was there, he said, but to discharge a debt of friendship…. But Lincoln was not relying on sympathy alone to win his case. In closing he reviewed the evidence, showing that all depended on Allen's testimony, and this he said he could prove to be false. Allen never saw Armstrong strike Metzker by the light of the moon, for at the hour when he said he saw the fight, between ten and eleven o'clock, the moon was not in the heavens. Then procuring an almanac, he passed it to the judge and jury. The moon, which was on that night only in its first quarter, had set before midnight. [Footnote: The Life of Abraham Lincoln, Vol. I, p. 272. Ida M. Tarbell. The Doubleday & McClure Co.]
An arguer should also be extremely careful to use evidence that on its face appears reasonable. Only an extremely credulous audience will accept ideas that run counter to human belief and experience. To attribute the occurrence of an event to supernatural causes would bring a smile of derision to any but a most ignorant and superstitious person. To attribute to men qualities and characteristics that human experience has shown they do not possess will bring equal discredit. No one is likely to accept evidence that contradicts his habits of thinking, that is contrary to what his life and experience have taught him is true. For this reason savage people are slow to believe the teachings of the Christian religion. For this reason it is difficult to make an audience believe that any one will deliberately and consistently work against his own interests, or follow any other unusual line of action. Evidence contrary to human experience may be true, but unless the exigencies of the argument demand its use, the arguer will do well to omit it entirely. If he is obliged to use it, he should make it appear as reasonable as he can, and also substantiate it with careful proof.
Huxley appreciated the fact that evidence, to be believed, must be in accordance with man's experience when he wrote the following:—
If any one were to try to persuade you that an oyster shell (which is also chiefly composed of carbonate of lime) had crystallized out of sea-water, I suppose you would laugh at the absurdity. Your laughter would be justified by the fact that all experience tends to show that oyster-shells are formed by the agency of oysters, and in no other way.
The ease with which an argument that does not satisfy this requirement may be overthrown is clearly shown in the following extract from a student's forensic:—
To say that the Cuban reconcentrados sunk the Maine in an effort to embroil the United States in a conflict with Spain is the veriest foolishness. There is not one scrap of documentary evidence to show that such was the case. Moreover, such an act would be unparalleled in the annals of history. It is unreasonable, contrary to all experience, that those oppressed people should have brought disaster, involving the destruction of property and the loss of many lives, upon the very nation that they were looking to for assistance.
(2) Is the evidence first-hand or hearsay evidence?
It is universally recognized that hearsay evidence is unreliable. A narrative is sure to become so garbled by passing from mouth to mouth that unless a witness can testify to a fact from his own personal knowledge the evidence he gives is worthy of little credence. There is sufficient chance for error when the person who witnessed the event relates the account himself; if the story is told by a second, and perhaps by a third person, it is likely to reflect but little of what really happened. Every one is familiar with the exaggerations of common rumor; it distorts facts so that they are unrecognizable. The works of Herodotus are untrustworthy because he frequently believed hearsay evidence. Since second-hand evidence both fails to establish anything worth while, if allowed to stand, and is easily overthrown even by a very little first-hand evidence, an arguer will do well to follow the custom of the law courts, and, as a rule, exclude it altogether.
(3) Can the evidence be considered as especially valuable?