§ 160 (3). ARGUING IN A CIRCLE.-Another common form of the Fallacy of Illicit Assumption is presented by the fallacy called arguing in a circle; which consists in assuming for a premise the very proposition to be proved, or one obviously equivalent to it, or one that is formally involved in it.' When the argument does not extend beyond a single syllogism it is called a Hysteron Proteron (the First-last).'

161 (4). QUESTION-BEGGING TERMS.Another very common and very dangerous

the night, the causa cognoscendi is the wet ground, from which we infer the causa essendi, i. e., the rain. Logic is, however, concerned with the causa essendi only so far as it constitutes the causa cognoscendi ; and hence logically the distinction may be regarded as immaterial.

This occurs most frequently in the use of synonyms, and, as observed by Whately, is peculiarly favored by the composite character of our language. It can occur only where the proposition assumed is so obviously equivalent to the conclusion as to be evidently the result of a trick or inadvertence. In general the premises assumed are equivalent to, or imply, the conclusion; and the conclusion is arrived at by the substitution of an equivalent term; which is the very essence of ratiocination. Such assumptions are not only admissible, but inevitable. Otherwise all syllogisms would be fallacious,—as involving a petitio principii; and inference, inconceivable.

The following is a striking example of this fallacy : "Since every unjust act is inexpedient, then no unjust act is expedient; then no expedient act is unjust; then every expedient act is just." This has been given as a valid argument. But the premise is obviously but an inference from the conclusion, which is the principle of the reasoning; and for it the thesis has been illicitly substituted as the premise.

form of this fallacy is that of using questionbegging terms (which is also a case of the Fallacy of False Definition). It consists either in including in the formal definition of a term some unproved assumption, as being of the essence of the conception denoted, or in using the term without formal definition, as though such assumption were included in its meaning. By this method, the propositions from which our conclusions are to be deduced, instead of being proved as they ought to be, are unconsciously imbibed by the mind, with the definition, or with our conception of the term, and the conclusion thus in effect assumed. The power of this method of persuasion is well understood by many, and unscrupulously used— as, for example, by Hobbes and other supporters of governmental absolutism; who realize the truth of Rousseau's observation that "the strongest is not strong enough to continue always master, unless he transforms his power into a right, and obedience into a duty." But with the mass of writers the fallacious process, though none the less efficacious, is entirely unconscious. A notable example of this fallacy is usually given by political writers in their definitions of "the State "; which is simply

an independent society of men," but is usually defined so as to include in its essence absolute power, or some other theory of the

writer. Any recent work on Politics will serve to illustrate the fallacy.

2. Of the Tests of Illicit Assumption

162. ENUMERATION OF THE TESTS. There are numerous tests by which the legitimacy of assumed premises may be determined, of which the most important and familiar are: (1) the "Instance," or Extreme Case "; (2) the "Burden of Proof," or Onus Probandi; and (3) the Reductio ad Absurdum. These will next be considered.

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§ 163. THE INSTANCE, OR EXTREME CASE. This test applies most appropriately to the Fallacy of Illicit Generalization, and is most efficacious in its operation; though, as is observed by De Morgan, it is commonly regarded as not only inadmissible, but impertinent. It consists simply in adducing an exception to the proposition assumed. The subject is admirably treated by the author cited."

164. THE ONUS PROBANDI. - An extremely effective means of testing the truth of 'The term "instance" is commonly used as synonymous with “example,” but it is said by De Morgan that by the medieval logicians it was always used to denote an inconsistent example, or, in other words, to denote what we would call an instance to the contrary,-an expression that would have been regarded by them as tautological.

2"The application of the extreme case is very often the only test by which an ambiguous assumption can be dealt

a proposition, and of thus exposing an Illicit Assumption, is often afforded by considering what is the presumption in the case; or, contrariwise, on which side of the question lies the burden of proof, or onus probandi. In general, this is on the party affirming the proposition, and, in the absence of other presumptions, we are always entitled to demand his proofs. This simple test will be sufficient to dispose of all propositions for which proofs cannot be found, but which have been inadvertently assumed; and this test we should always apply to our own reasoning, remembering that "Slowness of belief and distrust are the very sinews of wisdom." But in certain cases, and especially in Moral and Political Science, the test will often have a conclusive efficacy. For in Morality, Public and Private, or in Jurisprudence or Right, the questions presented are generally questions, not of fact, but of right and wrong; and among these there are certain fundamental principles, as, e. g., touching the right of personal liberty or security or selfownership, with reference to which the presumption is clearly defined, and its contradictory obviously absurd. Of this kind is the general presumption in favor of liberty; which, of

with; no wonder that the assumer should dread and protest against a process which is as powerful as the sign of the cross was once believed to be against evil spirits."-Formal Logic.

itself, is sufficient to dispose of numerous and important political theories that, from a neglect to consider the onus probandi, have been carelessly or dishonestly assumed.

$165. OF THE REDUCTIO AD ABSURDUM. -This consists in reasoning from the conclusion deduced from the premises assumed to some absurd, or admittedly untrue, conclusion; and this method of refutation will apply not only to the fallacy of illicit generalization, but to all forms of petitio principii whatever. It is, indeed, one of the most efficacious means that Logic has at its command for the detection of fallacy, and will therefore repay an attentive consideration.

Strictly speaking, the phrase would seem to indicate that it applies only to the establishment of the contradictory of the proposition under consideration '; but the method has, in fact, a much wider application, and the term, in common use, a corresponding extension. For it is the essential characteristic of all true

1 In the narrower sense, the term reductio ad absurdum is equivalent to the reductio ad impossibile; of which examples are given supra (§ 96, n.). But more generally it is used as including all cases where, from the conclusion of an argument, the contradictory of some admitted propositionor, in other words, a conclusion contrary to the hypothesis -can be deduced. Hence it is called by Aristotle the "Argument from Hypothesis." (Mansel's Aldrich, App., note I, p. 228.)