The requirement that every separate bit of evidence in an argument shall be consistent with every other bit of evidence in the same argument is too well understood to need explanation. One familiar with courts of law knows that a witness who contradicts himself is not believed. Furthermore, if the testimony of several witnesses for the same side is inconsistent, the case for that side is materially weakened. So it is in general debate: the arguer who wishes to succeed must not use evidence that is self-contradictory. His proof must "hang together"; his facts must all go to establish the same conclusion.

A flagrant violation of this principle once occurred in a class-room debate. The speaker for the negative on the proposition, "_Resolved_, That freshmen should be ineligible for college teams," said that such a rule would deprive the freshmen of much- needed physical exercise. Later on, he said that just as many freshmen would receive injuries under this rule as without it, since they would take part in equally dangerous contests as members of freshmen teams. This contradiction ruined his argument.

In the next place, evidence to be of any value whatever, must be consistent with what is known about the case. If an arguer is so careless as to make statements contradictory either to well- established facts or to facts easily proved, he cannot hope to attain the slightest measure of success. Only one guilty of gross neglect or absolute falsehood is likely to fall into such an error. At one time the story was circulated that, during his early life, Lincoln had been insane. In the following passage Ida M. Tarbell shows that the testimony on which this belief was founded is inconsistent with the known facts of the case, and is, therefore, palpably untrue:--

"Mr. Thornton went on to say that he knew beyond a doubt that the sensational account of Lincoln's insanity was untrue, and he quoted from the House journal to show how it was impossible that, as Lamon says, using Herndon's notes, 'Lincoln went crazy as a loon, and did not attend the legislature in 1841-1842, for this reason'; or, as Herndon says, that he had to be watched constantly. According to the record taken from the journals of the House by Mr. Thornton, which have been verified in Springfield, Mr. Lincoln was in his seat in the House on that 'fatal first of January' when he is asserted to have been groping in the shadow of madness, and he was also there on the following day."

Lincoln himself was an expert at detecting inconsistency wherever it existed. He won many of his lawsuits by the straightforward method of showing that the one or two vital statements on which the whole case of the opposition rested were false, inasmuch as they were inconsistent with well-established and incontrovertible facts. An instance of this sort is here described:--