In the course of the Lincoln-Douglas debate a question was put by Lincoln to Douglas, as follows:  “Can the people of a United States territory in any lawful way, against the wish of any citizens of the United States, exclude slavery from its limits, prior to the formation of a state constitution?” The question may be viewed as the source of a dilemma, both in the practical and in the syllogistic sense of the term.  In fact it involved a situation which, syllogistically, comprised more than one dilemma.  They may be stated as follows: 

I. If Douglas answers yes, he offends the South, and if he answers no, he offends the North;

But he must answer either yes or no;

Therefore he will offend either the South or the North.

II.  If Douglas offends the South, he loses the nomination for the Presidency in the next convention; and if he offends the North, he loses the election to the United States Senatorship (and his chances for the Presidency);

But he must offend either the South or the North;

Therefore he loses either the Presidency or the Senatorship.

Or, III.  If Douglas offends the South, he cannot become President; and if he offends the North, he cannot become President;

But he must offend either the South or the North;

Therefore he cannot become President.[45]

The dilemma, if it leaves no hole for the other side to creep through, is an extremely effective argument in politics and in competitive debate.  If you can thus get your adversary between the devil and the deep sea on a point that in the eyes of your audience is interesting and critical, you have crippled his case.  But if the point is not momentous, though your audience may find the dilemma amusing, you run the risk of the reproach of “smartness” if you crow very loudly over it.

On the other hand, a dilemma that is not exhaustive will hold no one.  Many of the arguments against the imposition of a federal tax on corporations assumed that if the tax were imposed it would soon be made unreasonable in amount.  Most arguments that the other side will abuse any power that is given to them may be regarded as falling into the class of incomplete dilemma.  A speaker who uses a leaky dilemma must have great confidence in the unintelligence of his audience, but it is surprising to see how often such dilemmas occur in political debates.

45.  Reasoning from Circumstantial Evidence.  The third type of reasoning from similarity named on page 120 is reasoning from circumstantial evidence.  The term is familiar to every one from murder trials and detective stories.  Webster’s argument in the White Murder Case, from which I print a short extract on page 157, is a famous example of an argument on circumstantial evidence; and in fiction Sir Conan Doyle has created for our delectation many notable and ingenious cases of it.  But reasoning from circumstantial evidence is far from being confined to criminal cases and fiction; as Huxley points out (see p. 241), it is also the basis of some of the broadest and most illuminating generalizations of science; and the example below from Macaulay is only one of innumerable cases of its use in history.