Imágenes de páginas
PDF
EPUB

to be proved. The advantages are, that, as the evidence commonly comes from several witnesses and different sources, a chain of cir. cumstances is less likely to be falsely prepared and arranged, and falsehood and perjury are more likely to be detected and fail of their purpose. The disadvantages are, that a jury has not only to weigh the evidence of facts, but to draw just conclusions from them; in doing which, they may be led by prejudice or partiality, or by want of due deliberation and sobriety of judgment, to make hasty and false deductions; a source of error not existing in the consideration of positive evidence.”

SECTION III.

DEDUCTION AND INDUCTION.

Deduction.

From the point of view of logic, arguments may be classified according as they move from the general to the specific, - DEDUCTION,2 — or from the specific to the general, -- INDUCTION.3

A simple example of DEDUCTION has come down to us from Aristotle: “All men are mortal, Socrates is a man, therefore Socrates is mortal.” In saying that “all men are mortal,” we assert that every member of a class designated as “men” is mortal ; in saying that “Socrates is a man," we assert that Socrates belongs to the class designated as “men;” in saying that “Socrates is mortal,” we assert that what we have said concerning the class to which Socrates belongs is true of Socrates. The two assertions "all men are mortal ” and “ Socrates is a man are called the premisses ; 4 the asser

[ocr errors]
[ocr errors]

1 Chief Justice Shaw, in the case of John W. Webster, indicted for the murder of George Parkman. Reported by George Bemis.

2 From de, from, and ducere, to lead.
8 From in, into, and ducere, to lead.
4 Praemissa, from prae, before, and mittere, to send or put.

6

tion deduced from the premisses, the assertion "Socrates is mortal,” is called the conclusion ;1 the three assertions taken together constitute what is called a syllogism.2

In every valid syllogism, as in the typical example just given, the conclusion inevitably follows from the premisses; for it contains nothing that is not in the premisses. In saying that “all men are mortal” and that “Socrates is a man,” we say by implication that “ Socrates is mortal.” The statement of the syllogism in full enables one to see clearly the premisses from which the conclusion is deduced.

A deductive argument may be presented in various forms. For example:

(1) Laws that cannot be enforced should be repealed; the law prohibiting the sale of intoxicating liquors cannot be enforced ; this law should, therefore, be repealed.

(2) If laws cannot be enforced, they should be repealed; the law prohibiting the sale of intoxicating liquors cannot be enforced; this law should, therefore, be repealed.

(3a) Laws that cannot be enforced should be repealed; the law prohibiting the sale of intoxicating liquors should, therefore, be repealed.

(36) The law prohibiting the sale of intoxicating liquors cannot be enforced, and should, therefore, be repealed.

(3c) The law prohibiting the sale of intoxicating liquors should be repealed, for it cannot be enforced.

The only difference between syllogisms (1) and (2) is in the manner of stating the first premiss; in (1) the assertion concerning laws that cannot be enforced rests on the assumption that such laws exist; in (2) the same assertion rests on the hypothesis that such laws exist, that is, it is conditional. The abridged syllogisms (3a), (36), and (3c) differ from (1) and

1 Conclusus, from con-, together, and claudere, to close.

? Eviloylouós, a reckoning all together, from oúv, together, and λογίζεσθαι, to reason.

(2) in the omission of the second premiss from (3a), of the first premiss from (36) and (3c), – omissions that are readily supplied.

A syllogism with one or more of its parts suppressed, as (3a), (36), or (3c) in the example just given, is called an enthymeme." In practical life reasoning is usually conlucted in this abridged form. For example:

99

The income tax is unzqual in its operation; therefore, it cannot last.

The income tax is justifiable, for it tends to diminish inequality in the distribution of wealth.

“ Robinson Crusoe ” must be an allegory, for Defoe says it is.

“Robinson Crusoe must be a true story, everything is so minutely described.

Greek, being a dead language, is of no use to living men.

As Greek literature is the source of what is best in modern liter. ature, knowledge of it is an essential part of a liberal education.

A college student should be free to choose his studies, for he can profit by no study which he is forced to pursue.

Certain studies every college student should pursue, for they are the foundations of culture.

The wearing of high hats at the theatre should be forbidden by law, for high hats are a nuisance to short men.

A law prohibiting the wearing of high hats at the theatre is restrictive of liberty, and laws restrictive of liberty are impolitic.

“ In a rude state of society, men are children with a greater variety of ideas. It is therefore in such a state of society that we may expect to find the poetical temperament in its highest perfection.”

1 'Evbúunua, from év@vuelo bai, to keep in mind, consider, infer; from év, in, and duuós, mind. For the history of the change in meaning which this word has undergone, see Murray's “ New English Dictionary," and De Quincey's essay on “Rhetoric.”

Macaulay : Essays; Milton.

2

“ If he has never been on a quest for buried treasure, it can be demonstrated that he has never been a child.” 1

“ It is well known that most students are at a disadvantage in attacking any subject, because their minds are untrained.” 2

“ The law was unconstitutional also, counsel averred, for the reason that it was class legislation.” 8

“When it [the new German constitution] was first published, the London Times remarked, in all seriousness, that it was sufficiently illogical to justify the hope that it would work well.” 4

• Why is our food so very sweet?
Because we earn before we eat.'»5

Fallacies of deduction.

The principal fallacies of deductive argument are beg

ging the question, technically known as petitio

principii, and arguing beside the point, technically known as ignoratio elenchi.6 To beg the question is to deduce a conclusion from

an assumed premiss and then to use the conBegging the question. clusion so reached as proof of the proposition originally assumed. The nature of this fallacy (often called “arguing in a circle”) may be learned from the following anecdote:

A woman, on seeing a very small porringer, said to a child, “ That must have been the little wee bear's porringer, it is so small,” and then added, “He must have been smaller than we thought, must n't he?” To assume that the bear was very small in order to prove that the porringer was his, and then from the fact that the porringer is small to infer that the bear must have been very small, is, manifestly, to beg the question.

1 R. L. Stevenson: Memories and Portraits; A Humble Remonstrance. 2 Charles Dudley Warner. Harper's Magazine, March, 1895, p. 645.

8 Report of W. D. Guthrie's argument before the United States Supreme Court in the income-tax cases : The Boston Herald, March 8, 1895.

4 The (New York] Nation, March 14, 1895, p. 205.
6 Nathaniel Cotton : Fables; The Bee, the Ant, and the Sparrow.
6 Literally, “ignoring the refutation."

Another example is given by Stephen :

“ A ship is cast away under such circumstances that her loss may be accounted for either by fraud or by accident. The captain is tried for making away with her. A variety of circumstances exist which would indicate preparation and expectation on his part if the ship really was made away with, but which would justify no suspicion at all if she was not. It is manifestly illogical, first, to regard the antecedent circumstances as suspicious, because the loss of the ship is assumed to be fraudulent, and, next, to infer that the ship was fraudulently destroyed from the suspicious character of the antecedent circumstances.” 1

[ocr errors]
[ocr errors]

A single word may involve a begging of the question. Disbelievers in Mr. Bellamy's view of the future beg the question when they speak of his Question“ Utopia;” for Utopia is understood to mean words. an unattainable ideal. An English journal declares that Mr. Leslie Stephen uses a “question-begging epithet” when he calls Tito Melema a “feminine ” character. In the title of Mill's essay on “The Subjection of Women," the word “subjection” begs the question by assuming that the present condition of woman is one of subjection to man, - a point to be proved. The title of Dr. Bushnell's work on woman suffrage “ The Reform against Nature" - begs the question by assuming that the proposed reform is “against nature.” Those who deem the game of foot-ball an important means of physical education maintain that those who call the game “brutal” beg the question by applying to the game itself an epithet deserved by some players. The following instance of question-begging is given by Bentham:

“ Take, for example, improvement and innovation: under its own name, to pass censure on any improvement might be too bold :

1 Sir James Fitzjames Stephen: Introduction to the Indian Evidence Act, chap. ii.

« AnteriorContinuar »