Part 15 (1/2)

Lincoln knew that this doctrine that no state could interfere with slavery would be intolerable to the people of Illinois, before whom he was carrying on his campaign; and this syllogism made clear to them the consequences of the decision of the Supreme Court.

Or you can use a syllogism to make obvious a flaw in the reasoning of your opponent, as in the following example:

In view of the history of commission government in this country so far as it has been made, the burden of proof rests with those who attempt to show that a government which has been so successful in cities of moderate size will not be successful in our largest cities. The syllogism they are required to prove runs briefly thus:

Commission government is acknowledged to have been successful in cities as large as one hundred and thirty thousand inhabitants, but

It has not been tried in cities containing more than one hundred and thirty thousand inhabitants;

Therefore, it will not be successful in cities of four hundred thousand or larger, which is a _reductio ad absurdum_.

The folly of the attempt is shown by the very statement of the conclusion.[44]

44. The Dilemma. One special form of the syllogism is at times so strong an argument that it deserves special mention here, namely, the dilemma. This is a syllogism in which the major premise consists of two or more hypothetical propositions (that is, propositions with an ”if”

clause) and the minor of a disjunctive proposition (a proposition with two or more clauses connected by ”or”).

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 const.i.tution?” 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 Senators.h.i.+p (and his chances for the Presidency);

But he must offend either the South or the North;

Therefore he loses either the Presidency or the Senators.h.i.+p.

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 compet.i.tive 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 a.s.sumed 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 cla.s.s 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 Circ.u.mstantial Evidence. The third type of reasoning from similarity named on page 120 is reasoning from circ.u.mstantial 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 circ.u.mstantial evidence; and in fiction Sir Conan Doyle has created for our delectation many notable and ingenious cases of it. But reasoning from circ.u.mstantial 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.

Reasoning from circ.u.mstantial evidence differs from reasoning from a.n.a.logy or generalization in that it rests on similarities reaching out in a number of separate directions, all of which, however, converge on the case in hand. This convergence is pointed out by Macaulay in the following admirable little argument on the authors.h.i.+p of the _Junius Letters_, which were a series of pseudonymous and malignant attacks on the British government about 1770:

Was he [Francis] the author of the Letters of Junius? Our own firm belief is that he was. The evidence is, we think, such as would support a verdict in a civil, nay, in a criminal proceeding. The handwriting of Junius is the very peculiar handwriting of Francis, slightly disguised.

As to the position, pursuits, and connections of Junius, the following are the most important facts which can be considered as clearly proved: first, that he was acquainted with the technical forms of the secretary of state's office; secondly, that he was intimately acquainted with the business of the war office; thirdly, that he, during the year 1770, attended debates in the House of Lords, and look notes of speeches, particularly of the speeches of Lord Chatham; fourthly, that he bitterly resented the appointment of Mr. Chamier to the place of deputy secretary-at-war; fifthly, that he was bound by some strong tie to the first Lord Holland. Now, Francis pa.s.sed some years in the secretary of state's office. He was subsequently chief clerk of the war office. He repeatedly mentioned that he had himself, in 1770, heard speeches of Lord Chatham; and some of these speeches were actually printed from his notes. He resigned his clerks.h.i.+p at the war office from resentment at the appointment of Mr. Chamier. It was by Lord Holland that he was first introduced into the public service. Now, here are five marks all of which ought to be found in Junius. They are all five found in Francis.

We do not believe that more than two of them can be found in any other person whatever. If this agreement does not settle the question, there is an end of all reasoning on circ.u.mstantial evidence.[46]

Here the five points or marks of similarity between the writer of the letters and Philip Francis are of such diversity that it would be an extraordinary coincidence if there had happened to be two men whom they would fit: where so many lines converge so closely at a single point it would hardly be possible for them to meet on more than one person.

The following brief extract from Webster's argument in the White Murder Case shows the same sort of convergence of similarities: each circ.u.mstance in itself is hardly strong enough to furnish ground for an argument on a.n.a.logy, but taken all together they point irresistibly in one direction, namely, to the fact of a conspiracy.