FALLACY (Lat. fallacia, deception, from fallax, deceitful, from fallere, to deceive; con nected with Gk. crIgiNNew, sphallein, to overthrow, Skt. phal, to deceive. Lith. pa/1i, OHG. fallen, Ger. fallen, Icel. fallay, AS. feallan, Eng. fall). The incorrect performance of the process of rea soning, so as to lead to error. The science of logic reduces sound reasoning to certain rules, and when any of these rules is violated, a logical fallacy is the result. There has been much dis mission as to the proper classification of fallacies, and even now' no agreement has been reached. But it is obvious that as a fallacy is a violation of some logical law. an adequate exhibition of the laws of thought will carry with it an ade quate exhibition of the possible fallacies. There is only one further difficulty. Language is not a perfect instrument for the expression of thought; and the same kind of logical mistake may be expressed in several ways, and each one of these modes of expression may be important enough to require treatment. This would lead to the old traditional classiticaiion into fallacies not complicated by verbal d ifficulties diclionem) and those so complicated (in dic Hone). Those not complicated by verbal dini en li. ieS need no detailed treatment, ns they are all obvious violations of some logical rule. All that need be done here is to give the names of sonic of the most emumon fallacies rxlra dfrii0//CM. the fallacy of the andistriladed is a violation of the syllogistic law' that the middle term must be distributed at least once. The illicit process of the major or minor term is a violation of the syllogistic law that neither extreme (major or minor) must appear in the conclusion with a quantity exceeding that be longing to it in the premises. The quatcrnio tcr mino•uni, or [Our terms, violates the law that a syllogism must have three, and only three, terms. Thu double negative violates the law that at least one of the premises of every syllogism that is reduced to proper expression must be affirmative. The pctitio principii, in the form in which it be longs here, violates the rule that there must be three distinct propositions in a syllogism; the violation occurs when the conclusion to he proved is assumed as a premise. But any really signifi cant petitio pri-ncipii is a fallacy in dietiww, for it is only when the identity of conclusion and premise is masked that a petitio principii is liable to be seriously made or seriously taken. Still another form of the petitio principii, called circulus in probando, is a fallacy extra dictioncm which is possible only when there are two or more syllogisms interrelated in such a way that the conclusion of each syllogism is the premise of some other. In this way the conclusion, or what is proved, in one syllogism is used in another syllogism as a basis of proof for a proposition which in its turn ultimately conies to be used as a basis of proof for the first conclusion. Hence the Latin name, meaning a circular process of reasoning. In English this fallacy is often called a vicious circle. The term petitio principii is sometimes applied to arguments which are not fallacious at all, but which employ as premises propositions the truth of which is not admitted by those to whom the argument is addressed. The fallacy of the consequent is a violation of the law that in hypothetical propositions the truth of the apodosis (consequent) is not to be taken as carrying with it the truth of the pro tasis (antecedent). Non causa pro cause, post
hoc ergo propter hoc, and false cause are names of a fallacy which consists in violating the induc tive canon that a temporal antecedent must be distinguished from a cause. The fallacies in dictione are not usually classified according to any systematic principle, but names are given to the most frequent or the most subtle of them. A very comprehensive distinction is that between fallacies in which the disguise of the illogical operation is effected by a single word (equivoca tion), and those in which it is effected by the structure or other peculiarity of a sentence or phrase as a whole (amphiboly). Equivocation or amphiboly, when it appears in the middle term of a syllogism, is called an ambiguous mid dle. If the equivocation arises from misplaced emphasis or accent, it is called the fallacy of accent. The so-called fallacies of composition and division may be either equivocations or amphibolies. Thus 'all men' may mean either every man singly (distributive) or the totality of mankind taken as a unit (collective). Any violation of logical rules arising from failure to make this distinction is a fallacy of composition when the distributive use is mistaken for the collective; in the reverse ease there is a fallacy of division. These same fallacies of composition and division are amphibolies when the ambiguity between distributive and collective use lurks not in a single word (as above in the but in a phrase. Thus, from the two premises "The animals walk by two and two," and -Two and two are four," to argue that "The animals walk by fours" is a fallacy of composition aris ing from an amphiboly. Another may in which a fallacy may arise is from neglect to observe a qualification tacitly but really made. Thus the statement "What I bought yesterday, I ate to day," in civilized communities really means "What I bought in the marketable form yester day, I ate to-day after it had undergone whatever change was necessary to make it edible." If now ft caviler, refusing to recognize these tacit quali fications, were to say "You bought raw meat yes terday, didn't you?" he would suggest the infer ence that I ate raw meat to-day. In this case the qualifications really made in the premises are ignored in drawing the conclusion. This is called argumentum a dicta simplicitcr ad dictum sccundunt quid—reasoning from statements true in general as if they were true under every quali fication.
Another form of fallacy screened by verbal expression is that in which a conclusion is estab lished which in expression resembles the point one starts out to make, but which in reality has nothing to do with that point. This is called ignimatio elenchi or irrelevant conclusion. The so-called fallacy of complex question is nothing but an unwarranted assumption in putting a question. The stock example is the inquiry, "Have you stopped beating your mother ?" As can be seen from this brief treatment, many of the fallacies that have time-honored names are not to be taken very seriously. They are relies of an age given to verbal quibbling. It is more important to know what the fundamental laws of thought are, than to know the names given to many trifling and playful violations of such laws. For some other technical terms used to denote improper forms of argumentation, see ARGUMENT. Consult : Sidgwick, Follucies (Lon don, 1883) ; and the logics of Mill, Creighton, etc. See also LOGIC; INDUCTION; SYLLOGISM.