personal interests at stake.
Argumentum ad baculum (argument to the club) is a kind of argument that appeals to a threat or to fear in order to support a conclusion, or to intimidate a respondent into accepting it. Ad baculum arguments often take an indirect form; e.g., ‘If you don’t do this, harmful consequences to you might follow’. In such cases the utterance can often be taken as a threat. Ad baculum arguments are not inherently fallacious, because appeals to threatening or fearsome sanctions – e.g., harsh penalties for drunken driving – are not necessarily failures of critical argumentation. But because ad baculum arguments are powerful in eliciting emotions, they are often used persuasively as sophistical tactics in argumentation to avoid fulfilling the proper requirements of a burden of proof.
Argument from authority is a kind of argument that uses expert opinion (de facto authority) or the pronouncement of someone invested with an institutional office or title (de jure authority) to support a conclusion. As a practical but fallible method of steering discussion toward a presumptive conclusion, the argument from authority can be a reasonable way of shifting a burden of proof. However, if pressed too hard in a discussion or portrayed as a better justification for a conclusion than the evidence warrants, it can become a fallacious argumentum ad verecundiam (see below). It should be noted, however, that arguments based on expert opinions are widely accepted both in artificial intelligence and everyday argumentation as legitimate and sound under the right conditions. Although arguments from authority have been strongly condemned during some historical periods as inherently fallacious, the current climate of opinion is to think of them as acceptable in some cases, even if they are fallible arguments that can easily go wrong or be misused by sophistical persuaders. Argumentum ad judicium represents a kind of knowledge-based argumentation that is empirical, as opposed to being based on an arguer’s personal opinion or viewpoint. In modern terminology, it apparently refers to an argument based on objective evidence, as opposed to somebody’s subjective opinion. The term appears to have been invented by Locke to contrast three commonly used kinds of arguments and a fourth special type of argument. The first three types of argument are based on premises that the respondent of the argument is taken to have already accepted. Thus these can all be called ‘personal’ in nature. The fourth kind of argument – argumentum ad judicium – does not have to be based on what some person accepts, and so could perhaps be called ‘impersonal.’ Locke writes that the first three kinds of arguments can dispose a person for the reception of truth, but cannot help that person to the truth. Only the argumentum ad judicium can do that. The first three types of arguments come from ‘my shamefacedness, ignorance or error,’ whereas the argumentum ad judicium ‘comes from proofs and arguments and light arising from the nature of things themselves.’ The first three types of arguments have only a preparatory function in finding the truth of a matter, whereas the argumentum ad judicium is more directly instrumental in helping us to find the truth. Argumentum ad verecundiam (argument to reverence or respect) is the fallacious use of expert opinion in argumentation to try to persuade someone to accept a conclusion. In the Essay concerning Human Understanding (1690) Locke describes such arguments as tactics of trying to prevail on the assent of someone by portraying him as irreverent or immodest if he does not readily yield to the authority of some learned opinion cited. Locke does not claim, however, that all appeals to expert authority in argument are fallacious. They can be reasonable if used judiciously.
Argumentum ad ignorantiam (argument to ignorance) takes the following form: a proposition a is not known or proved to be true (false); therefore A is false (true). It is a negative type of knowledge-based or presumptive reasoning, generally not conclusive, but it is nevertheless often non-fallacious in balance-of-consideration cases where the evidence is inconclusive to resolve a disputed question. In such cases it is a kind of presumption-based argumentation used to advocate adopting a conclusion provisionally, in the absence of hard knowledge that would determine whether the conclusion is true or false. An example would be: Smith has not been heard from for over seven years, and there is no evidence that he is alive; therefore it may be presumed (for the purpose of settling Smith’s estate) that he is dead. Arguments from ignorance ought not to be pressed too hard or used with too strong a degree of confidence. An example comes from the U.S. Senate hearings in 1950, in which Senator Joseph McCarthy used case histories to argue that certain persons in the State Department should be considered Communists. Of one case he said, ‘I do not have much information on this except the general statement of the agency that there is nothing in the files to disprove his Communist connections.’ The strength of any argument from ignorance depends on the thoroughness of the search made. The argument from ignorance can be used to shift a burden of proof merely on the basis of rumor, innuendo, or false accusations, instead of real evidence.
Ignoratio elenchi (ignorance of refutation) is the traditional name, following Aristotle, for the fault of failing to keep to the point in an argument. The fallacy is also called irrelevant conclusion or missing the point. Such a failure of relevance is essentially a failure to keep closely enough to the issue under discussion. Suppose that during a criminal trial, the prosecutor displays the victim’s bloody shirt and argues at length that murder is a horrible crime. The digression may be ruled irrelevant to the question at issue of whether the defendant is guilty of murder. Alleged failures of this type in argumentation are sometimes quite difficult to judge fairly, and a ruling should depend on the type of discussion the participants are supposed to be engaged in. In some cases, conventions or institutional rules of procedure – e.g. in a criminal trial – are aids to determining whether a line of argumentation should be judged relevant or not. Petitio principii (asking to be granted the ‘principle’ or issue of the discussion to be proved), also called begging the question, is the fallacy of improperly arguing in a circle. Circular reasoning should not be presumed to be inherently fallacious, but can be fallacious where the circular argument has been used to disguise or cover up a failure to fulfill a burden of proof. The problem arises where the conclusion that was supposed to be proved is presumed within the premises to be granted by the respondent of the argument. Suppose I ask you to prove that this bicycle (the ownership of which is subject to dispute) belongs to Hector, and you reply, ‘All the bicycles around here belong to Hector.’ The problem is that without independent evidence that shows otherwise, the premise that all the bicycles belong to Hector takes for granted that this bicycle belongs to Hector, instead of proving it by properly fulfilling the burden of proof. The fallacy of many questions (also called the fallacy of complex question) is the tactic of packing unwarranted presuppositions into a question so that any direct answer given by the respondent will trap her into conceding these presuppositions. The classical case is the question, ‘Have you stopped beating your spouse?’ No matter how the respondent answers, yes or no, she concedes the presuppositions that (a) she has a spouse, and (b) she has beaten that spouse at some time. Where one or both of these presumptions are unwarranted in the given case, the use of this question is an instance of the fallacy of many questions. The fallacy of equivocation occurs where an ambiguous word has been used more than once in an argument in such a way that it is plausible to interpret it in one way in one instance of its use and in another way in another instance. Such an argument may seem persuasive if the shift in the context of use of the word makes these differing interpretations plausible. Equivocation, however, is generally seriously deceptive only in longer sequences of argument where the meaning of a word or phrase shifts subtly but significantly. A simplistic example will illustrate the gist of the fallacy: ‘The news media should present all the facts on anything that is in the public interest; the public interest in lives of movie stars is intense; therefore the news media should present all the facts on the private lives of movie stars’. This argument goes from plausible premises to an implausible conclusion by trading on the ambiguity of ‘public interest’. In one sense it means ‘public benefit’ while in another sense it refers to something more akin to curiosity.
Amphiboly (double arrangement) is a type of traditional fallacy (derived from Aristotle’s list of fallacies) that refers to the use of syntactically ambiguous sentences like ‘Save soap and waste paper’. Although the logic textbooks often cite examples of such sentences as fallacies, they have never made clear how they could be used to deceive in a serious discussion. Indeed, the example cited is not even an argument, but simply an ambiguous sentence. In cases of some advertisements like ‘Two pizzas for one special price’, however, one can see how the amphiboly seriously misleads readers into thinking they are being offered two pizzas for the regular price of one. Accent is the use of shifting stress or emphasis in speech as a means of deception. For