CHAPTER XIII

ILLICIT CONVERSIONS

183. SIMPLE CONVERSION OF UNIVERSAL AFFIRMATIVE PROPOSITION.-The most usual form of this fallacy occurs in the simple conversion of a universal affirmative proposition, as, e. g., where from the proposition "Y is X" we illicitly infer that "X is Y"; and to this form all other cases may be reduced. The fallacy is so obvious that it might be supposed it could not often occur, but it is in fact very

common.

Examples

184. CONFUSION OF PROPOSITION WITH JUDGMENT.—An example of it seems to be presented by the commonly received doctrine that "a proposition is a judgment expressed in words"; which seems to result from an illicit conversion of the proposition that a 'judgment expressed in words is a proposition.'

$ 185. ILLICIT CONVERSION BY NEGATION.

-The fallacy frequently occurs in the conversion of a proposition by negation or contraposition. Thus, e. g., the proposition "Y is not X" becomes by negation “ Y is not-X "; from which-converting per accidens-we may infer that Some not-X is Y"; but not—as is often inferred-that " All not-X is Y.”

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By this method any universal affirmative proposition (" Y is X") may be converted into a proposition between the negatives of its terms. (i. e., Not X is not Y); but not, as is often done, without converting the terms,-i. e., from the proposition " Y is X" we may infer that Not X is not Y," but not that "Not

Y is not X" (§ 91).

186. AN ARGUMENT OF HOBBES.-A striking example of this fallacy is presented by Hobbes, that prince of logicians. Justice he defines as the keeping of covenants, and injustice as the failure to keep them. But, according to his theory, covenants become valid only upon the institution of government, from which they derive their validity. Hence in a state of nature there is neither justice nor injustice. But he says also: "Whatever is not unjust is just," and this conclusion-which is contradictory to his main position is obviously arrived at by an illicit conversion of the universal affirmative proposition, "Whatever is just is not-unjust.

CHAPTER XIV

ILLICIT SUBSTITUTIONS OF TERMS

187. Substitutions of terms may consist either in the substitution of a new vocable or vocal sign, or in the substitution of a new sense to the same vocable. The latter is always illicit, and constitutes the Fallacy of Equivocation. The former will be considered in this, the latter in our next chapter.

The substitution of new terms of equivalent signification for terms originally occurring is the most common and extensive in application of all the processes involved in ratiocination; and the corresponding illicit processes- if we include equivocation - may be regarded as including all fallacies whatever. Hence the examples already given, and especially those given under the head of Irrelevant Conclusion, will serve equally well to illustrate the fallacy now under consideration.

Examples

§ 188. AUSTIN'S ARGUMENT.- Many examples of this fallacy are furnished by Austin,

as, e. g., in substituting for the predicate of the proposition that " The sovereign power is incapable of legal limitation," the term "legally despotic," and thus inferring from the former proposition that government is vested by law with despotic power; which is not only untrue, but upon his own theory impossible. For, if law is but an expression of the will of the sovereign, it is equally absurd to say either that the sovereign power" is limited" or that "it is conferred" by law.

$ 189. SPENCER'S ARGUMENT. Another example is furnished by Spencer in inferring from the "right of free exchange" the "right of free contract," which is in effect to substitute genus for species in the subject of a universal affirmative proposition. For exchange is only a species of contract (v. supra, § 181). It is true that the right of free contract cannot be doubted, but the substitution is none the less a logical fallacy.

$190. FLETCHER vs. PECK.-Still another example of this fallacy is furnished by ChiefJustice Marshall (the greatest and most logical of American jurists) in Fletcher vs. Peck, 6 Cranch, 135; where it was decided that an act of the Legislature of Georgia revoking a grant of land was in contravention of the provision of the Constitution of the United States forbidding the States to pass any act" impairing

the obligation of contracts." The argument in effect was that a grant is a contract, and that this was impaired by the act; which was in effect to substitute "Contract" for "Obligation of Contract." The fallacy is the more glaring from the fact that a grant is an executed contract, which carries with it no obligation. Hence the constitutional provision must be held to refer only to executory or obligatory