Posted on 12/19/2003 5:46:41 AM PST by general_re
. . . arguments, like men, are often pretenders.
— Plato
It would, be a very good thing if every trick could receive some short and obviously appropriate name, so that when anyone used this or that particular trick, he could at once be reproved for it.
— Arthur Schopenhauer
An argument, whatever its subject or sphere, is generally constructed in such a way as to prove that its conclusion is true. But any argument can fail to fulfill this purpose in either of two ways. One way it can fail is by assuming a false proposition as one of its premisses. We saw, in Chapter 1, that every argument involves the claim that the truth of its conclusion follows from, or is implied by, the truth of its premisses. So if its premisses are not true, the argument fails to establish the truth of its conclusion, even if the reasoning based on those premisses is correct. To test the truth or falsehood of premisses, however, is not the special responsibility of the logician; it is rather the task of inquiry in general, since premisses may deal with any subject matter whatever.
The other way in which an argument can fail to establish the truth of its conclusion is to rely upon premisses that do not imply the conclusion. Here we are in the special province of the logician, whose chief concern is the logical relations between premisses and conclusion. An argument whose premisses do not support its conclusion is one whose conclusion could be false even if all its premisses were true. In cases of this kind the reasoning is bad, and the argument is said to be fallacious. A fallacy is an error in reasoning.
The word "fallacy," however, as logicians use it, designates not any mistaken inference or false belief, but typical errors, that is, mistakes that arise commonly in ordinary discourse and that devastate the arguments in which they appear. Each fallacy, as we shall use that term, is a type of incorrect argument. An argument in which a mistake of a given type appears is said to commit that fallacy. Since each fallacy is a type, we can say of two or more different arguments that they contain or commit the same fallacy; that is, they exhibit the same kind of mistake in reasoning. An argument that contains or commits a fallacy of a given type may also be said to be a fallacy, that is, to be an example or instance of that typical mistake.
There are many ways in which reasoning can go astray; that is, there are many kinds of mistakes in argument. It is customary to reserve the term "fallacy" for arguments that, although incorrect, are psychologically persuasive. Some arguments are so obviously incorrect as to deceive and persuade no one. But fallacies are dangerous because most of us are, at one time or another, fooled by some of them. We therefore define a fallacy as a type of argument that may seem to be correct, but that proves, on examination, not to be so. It is profitable to study these mistaken arguments, because the traps they set can best be avoided when they are well understood. To be forewarned is to be forearmed!
Whether a given argument does in fact commit a fallacy may depend on the interpretation given to the terms used by its author. In a passage that appears to be fallacious, it may be difficult to determine out of context what meanings the author intended for the terms used. Sometimes the accusation of "Fallacy!" is unjustly leveled at a passage that was intended by its author to make a point missed by the critic — perhaps even to make a joke. We should bear such unavoidable complications in mind as we apply the analysis of fallacious argument to actual discourse. Our logical standards should be high, but our application of them to arguments in ordinary life should also be generous and must be fair.
How many different kinds of mistakes in arguments — different fallacies — may be distinguished? Aristotle, the first systematic logician, identified 13 types; recently a listing of more than 100 has been developed! There is no precisely determinable number of fallacies, however, since much depends, in counting them, on the system of classification used. We distinguish 17 fallacies here — the most common and most deceptive mistakes in reasoning — divided into three large groups, called a) fallacies of relevance; b) fallacies of presumption; and c) fallacies of ambiguity.
The grouping of fallacies is always in some degree arbitrary, because mistakes of one kind will bear close similarities to, and sometimes overlap with, mistakes of another kind. The placement of a given fallacious passage in one specific group is also often disputable, because there may be more than one mistake of reasoning in that passage. If one remains mindful of this unavoidable imprecision, gaining an understanding of the essential features of each of the three major categories and the specific features of its several sub-categories will be of much practical use. It enables one to detect the most troublesome errors in reasoning as they occur in ordinary discourse, and it promotes the logical sensitivity needed to detect related errors that may fall outside any one of these groupings.
When an argument relies on premisses that are not relevant to its conclusion, and that therefore cannot possibly establish its truth, the fallacy committed is one of relevance. "Irrelevance" may perhaps better describe the problem, but the premisses are often psychologically relevant to the conclusion, and this relevance explains their seeming correctness and persuasiveness. How psychological relevance can be confused with logical relevance can be explained in part by the different uses of language that we distinguished among in Chapter 4; the mechanics of these confusions will become clearer in the following analyses of the seven different fallacies in this group.
Latin names traditionally have been given to many fallacies; some of these — such as ad hominem — have become part of the English language. We will use here both the Latin and the English names.
The Argument from Ignorance: Argument Ad Ignorantiam
The argument ad ignorantiam (from ignorance) is the mistake that is committed when it is argued that a proposition is true simply on the basis that it has not been proved false, or that it is false because it has not been proved true. We realize, on reflection, that many false propositions have not yet been proved false, and many true propositions have not yet been proved true — and thus our ignorance of how to prove or disprove a proposition does not establish either truth or falsehood. This fallacious appeal to ignorance crops up most commonly in the misunderstandings incidental to developing science, where propositions whose truth cannot yet be established are mistakenly held to be false for that reason, and also in the world of pseudoscience, where propositions about psychic phenomena and the like are fallaciously held to be true because their falsehood has not been conclusively established.
Famous in the history of science is the argument ad ignorantiam given in criticism of Galileo, when he showed leading astronomers of his time the mountains and valleys on the moon that could be seen through his telescope. Some scholars of that age, absolutely convinced that the moon was a perfect sphere, as theology and Aristotelian science had long taught, argued against Galileo that, although we see what appear to be mountains and valleys, the moon is in fact a perfect sphere, because all its apparent irregularities are filled in by an invisible crystalline substance — an hypothesis that saves the perfection of the heavenly bodies and that Galileo could not prove false! Legend has it that Galileo, to expose the argument ad ignorantiam, offered another of the same kind as a caricature. Unable to prove the nonexistence of the transparent crystal supposedly filling the valleys, he put forward the equally probable hypothesis that there were, rising up from that invisible crystalline envelope, even greater mountain peaks — but made of crystal and thus invisible! And this hypothesis, he pointed out, his critics could not prove false.
Those who strongly oppose some great change are often tempted to argue against the change on the ground that it has not yet been proved workable or safe. Such proof often is impossible to provide in advance, and commonly the appeal of the objection is to ignorance mixed with fear. Such an appeal often takes the form of rhetorical questions that suggest, but do not flatly assert, that the proposed changes are full of unknown peril. Policy changes may be supported, as well as opposed, by an appeal to ignorance. When the federal government issued a waiver, in 1992, allowing Wisconsin to reduce the additional benefits it had been giving to welfare mothers for having more than one child, the governor of Wisconsin was asked if there was any evidence that unwed mothers were having additional children simply in order to gain the added income. His reply, ad ignorantiam, was this: "No, there isn't. There really isn't, but there is no evidence to the contrary, either."
In some circumstances, of course, the fact that certain evidence or results have not been obtained, after they have been actively sought in ways calculated to reveal them, may have substantial argumentative force. New drugs being tested for safety, for example, are commonly given to rodents or other animal subjects for prolonged periods; the absence of any toxic effect on the animals is taken to be evidence (although not conclusive evidence) that the drug is probably not toxic to humans. Consumer protection often relies on evidence of this kind. In circumstances like these, we rely not on ignorance but on our knowledge, or conviction, that if the result we are concerned about were likely to arise, it would have arisen in some of the test cases. This use of the inability to prove something true supposes that investigators are highly skilled, and that they very probably would have uncovered the evidence sought had it been possible to do so. Tragic mistakes sometimes are made in this sphere, but if the standard is set too high — if what is required is a conclusive proof of harmlessness that cannot ever be given — consumers will be denied what may prove to be valuable, even lifesaving, medical therapies.
Similarly, when a security investigation yields no evidence of improper conduct by the persons investigated, it would be wrong to conclude that the investigation has left us ignorant. A thorough investigation will properly result in their being "cleared." Not to draw a conclusion, in some cases, is as much a breach of correct reasoning as it would be to draw a mistaken conclusion.
The appeal to ignorance is common and often appropriate in a criminal court, where an accused person is presumed innocent until proved guilty. We adopt this principle because we recognize that the error of convicting the innocent is far more grave than that of acquitting the guilty - and thus the defense in a criminal case may legitimately claim that if the prosecution has not proved guilt beyond a reasonable doubt, the only verdict possible is not guilty. The United States Supreme Court strongly reaffirmed this standard of proof in these words:
The reasonable-doubt standard . . . is a prime instrument for reducing the risk of convictions resting on factual error. The standard provides concrete substance for the presumption of innocence — that bedrock axiomatic and elementary principle whose enforcement lies at the foundation of the administration of our criminal law
But this appeal to ignorance succeeds only where innocence must be assumed in the absence of proof to the contrary; in other contexts, such an appeal is indeed an argument ad ignorantiam.
And so I thought it might be useful to present an authoritative collection of common logical fallacies, of the type often encountered on the web and elsewhere. These are derived from Chapter 6 of Copi and Cohen's excellent text, Introduction to Logic, 10'th edition - it is a preferred text for many introductory college logic courses, due to its relatively clear and accessible style. I plan for this to be an ongoing series, covering the fallacies that are exposed therein - although they list seventeen fallacies, and I intend to cover all seventeen, some sections are somewhat shorter than others, so I may decide to combine them into a single posting. Finally, I have, for the most part, eliminated footnotes from the sections, except where I deem them to be particularly useful.
As I said, I intend to post all the parts over the coming days, whether there's any expressed interest or not. I hope that freepers will find it worthy of discussion - feel free to post examples of fallacies spotted "in the wild", or ask questions of others, and so forth - but even if not, I think it will be useful as a reference for the future. If there does prove to be sufficient interest, let me know, and I will put together a ping list for future installments in this series.
signed,
general_re's dog
I must have missed that - it looks as though the posting form has been somewhat revised of late, and I probably overlooked it.
Moderator: would you be so kind as to add "Philosophy" to the list of subjects for this thread?
One could imagine no greater present for this Holiday Season.... your generosity will not go unnoticed.
I think I know what the problem is - there's a difference in the topics list available in "News/Activism", which is the one you and I are familiar with, and the topics list here in "General Interest". Try it out - open two browser windows, one for News and one for Chat, hit "post" for both of them, and bring up the topic lists side-by-side. For whatever reason, "Philosophy" is not available as a topic here in General Interest - guess it's not something that freepers are "generally interested" in ;)
Anyway, that's why I missed it - it wasn't there in the first place...
I did. It was too dang inconvenient to monitor more than one forum before, for me and for most others, I think, which is why just about everything wound up in News - that's the forum most people chose to watch. But I'm guessing that I'm not alone in switching to the "all forums" view, which should hopefully make this place a bit less of a ghetto than in the past - it's a lot less invisible than it used to be if you switch over.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.