Cross-examination can expose the improbability of a witness’s testimony. The evidentiary authority for probing the improbability of a witness’s testimony is found in Evidence Rules 401 and 611. Rule 401 states the test for relevance: “Evidence is relevant if: (a) it has a tendency to make the existence of any  fact more or less probable.” Rule 611states that the court may “exercise reasonable control over the mode and order of examining witnesses and presenting evidence so as to (1) to make the procedures effective for determining the truth. . .” This provision of Rule 611(a) can convince the judge to overrule an objection to the cross that questions the improbability of the witness’s testimony. cross-examination to proceed. Rule 611(b) includes cross-examination matters: (1) within the scope of direct; (2) affecting credibility; or (3) that the court decides are pertinent.

One technique for impeaching a witness by showing improbability is to apply the logical form of argument referred to as “reduction to the absurd” or in Latin, “reductio ad absurdum.” This technique, also referred to as “proof by contradiction,” extends a premise of the witness out to an absurd or ridiculous result, making it implausible. The examiner asks, “If this premise is true, what else must follow?” The original premise and the absurd outcome cannot both be true.
In Cross-examination Handbook we used Clarence Darrow’s cross-examination of William Jennings Bryan in the Scopes trial, focusing on Darrow’s examination of adverse Bryan utilizing the reduction-to-the-absurd technique to defeat him. Bryan—a former candidate for President and head of the fundamentalist movement served as co-counsel for the prosecution. Clarence Darrow signed on as co-counsel for the defense. And, some say that the ordeal of the cross-examination contributed to Bryan’s death five days after the trial.
While most of Darrow’s cases have become long-forgotten footnotes in the history of U.S. jurisprudence, his legend lives on due to his performance as defense counsel in 1925 in the Scopes trial,” or “Dayton Monkey Trial.” John Thomas Scopes, a small-town, Dayton, Ohio high school teacher, was accused of teaching evolution in violation of a recently enacted Tennessee statute. Clarence Darrow’s cross-examination, which lasted a full day, reduced Bryan’s fundamentalist beliefs to the absurd. 
I’ve used Darrow’s cross in my CLE presentations on “Great Cross-Examinations in History and in the Movies” because it displays the reduction to the absurd technique being utilized to reveal improbabilities. The Scopes trial was fictionalized in a play “Inherit the Wind,” and later into a movie by the same name, starring Spencer Tracy as Matthew Harrison Brady (Darrow) and Fredric March as Henry Drummond (Bryan). The real-life cross-examination was even more dramatic than its Hollywood rendition. 
The courtroom was so packed that the judge moved the cross-examination outside for fear that the floor would collapse under the weight of spectators. Here is what the scene looked like.

Here is Darrow’s, I mean Brady’s, cross-examination of Bryan, I mean Drummond:
[Darrow locks Bryan into the premise.]
Darrow: Q. . . . Do you consider the story of Jonah and the whale a miracle?
Bryan: A. I think it is.
Q. Do you believe Joshua made the sun stand still?
A. I believe what the Bible says. I suppose you mean that the earth stood still?
Q. I don’t know. I am talking about the Bible now.
A. I accept the Bible absolutely.
Q. The Bible says Joshua commanded the sun to stand still for the purpose of lengthening the day, doesn’t it; and you believe it?
A. I do.
Q. Do you believe at that time the sun went around the earth?
A. No, I believe that the earth goes around the sun . . .
Q. . . . If the day was lengthened by stopping either the earth or the sun, it must have been the earth?
A. Well, I should say so.
Q. Yes? But it was the language that was understood at the time, and we now know that the sun stood still as it was with the earth.
A. Well, no —
Q. We know also the sun does not stand still?
A. Well, it is relatively so, as Mr. Einstein would say.
Q. I ask you if it does stand still?
A. You know as well as I know.
Q. Better. You have no doubt about it.
A. No. And the earth moves around.
Q. Yes? . . .
Q. Now, Mr. Bryan, have you ever pondered what would have happened to the earth if it had stood still suddenly?
A. No.
Q. Have you not?
A. No; the God I believe in could have taken care of that, Mr. Darrow.
[Darrow extends the premise to the absurd result.]
Q. I see. Have you ever pondered what would naturally happen to the earth if it stood still suddenly?
A. No.
Q. Don’t you know it would have been converted into a molten mass of matter?
A. You testify to that when you get on the stand. I will give you a chance.
[The examination continues later with inquiries about Adam, Eve, and the serpent.]
Darrow: Q. And you believe that came about because Eve tempted Adam to eat the fruit?
Bryan: A. Just as it says (in the Bible).
Q. And you believe that is the reason that God made the serpent to go on his belly after he tempted Eve?
A. I believe the Bible as it is, and I do not permit you to put your language in the place of the language of the Almighty. You read the Bible and ask me questions, and I will answer them. I will not answer your questions in your language.
Q. I will read it to you from the Bible, in your language. “And the Lord God said unto the serpent, because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go and dust shalt thou eat all the days of thy life.”
Do you think that is why the serpent is compelled to crawl upon his belly?
A. I believe that.
Q. Have you any idea how the snake went before that time?
A. No, sir.
Q. Do you know whether he walked on his tail or not?
A. No sir. I have no way to know.
Attorney for the Damned: Clarence Darrow in the Courtroom 193-198 (Arthur Weinberg ed., University of Chicago Press 1989)
Of course, the jury must be willing to accept that the principles endorsed by the witness are in fact absurd. It is highly questionable whether the Scopes jury, all from the heart of the Bible Belt, would have been favorably impressed by Darrow’s cross-examination of Bryan. A seldom-quoted portion of the transcript shows Darrow crossing over the line in a manner in which a modern jury would find reprehensible.
Here you can watch a portion of the cross in “Inherit the Wind:”