A21-Logic Lessons.txt Graham L. Kendall Modified 7/6/2003 http://www.grahamkendall.net/ Email grahamkendall74135@yahoo.com I am found on IRC Efnet/Undernet/Dalnet as glk See also http://www.infidels.org/news/atheism/logic.html Below is a list of some common fallacies, and also some rhetorical devices often used in debate. The list is not intended to be exhaustive. An argumentum ad verecundiam is an argument based on authority. The Latin means "appeal to reverence". (Here, authorities mean people presumed to be experts, as opposed to people holding power over others--ScottJohnson) Fallacious because: * Experts are often wrong. Perhaps less so than laypersons, but still so. * X may be a statement of opinion rather than fact; in many fields of study "expert opinion" (unsupported by empirical evidence) is considered conjecture and nothing more. * The expert community may be biased. Many a box-office hit has been rubbished by movie critics, for example. * X may not be agreed upon by all experts in the community; in many cases X is rejected by a minority of experts (but a minority of experts, or even only one, agree with X). Much quackery seems to fall into this category. * If a particular expert is named ("according to Dr. Sam Snakeoil..."), his expertese may be suspect. (Is this different from "experts may not agree" ? I find quoting a particular source more convincing than quoting a vague "experts say..." or "scientists say...".) * A world-famous expert in one field knows just as little as the average person in most others field, outside his area of expertise. * Experts are often mis-quoted, their statements taken out of context. Sometimes correct, because: * X may be in fact proven; or sufficiently well-demonstrated that it is near-universally regarded as fact. * Expert community may in fact agree that X is true. ARGUMENTUM AD BACULUM / APPEAL TO FORCE The Appeal to Force is committed when the arguer resorts to force or the threat of force in order to try and push the acceptance of a conclusion. It is often used by politicians, and can be summarized as "might makes right". The force threatened need not be a direct threat from the arguer. For example: "... Thus there is ample proof of the truth of the Bible. All those who refuse to accept that truth will burn in Hell." AD LAZERUM The fallacy Ad Lazerum is that the antiquity of an idea has no logical connection with its truth. By way of example, the *oldest* notion of the shape of the earth is that it is flat, with the sky a solid dome overhead. Said notion has survived down to the present day. ARGUMENTUM AD HOMINEM Argumentum ad Hominem is literally "argument directed at the man". The Abusive variety of Argumentum ad Hominem occurs when, instead of trying to disprove the truth of an assertion, the arguer attacks the person or people making the assertion. This is invalid because the truth of an assertion does not depend upon the goodness of those asserting it. For example: "Atheism is an evil philosophy. It is practised by Communists and murderers." Sometimes in a court of law doubt is cast upon the testimony of a witness by showing, for example, that he is a known perjurer. This is a valid way of reducing the credibility of the testimony given by the witness, and not Argumentum ad Hominem; however, it does not demonstrate that the witness's testimony is false. To conclude otherwise is to fall victim of the Argumentum ad Ignorantiam. The circumstantial form of Argumentum ad Hominem is committed when a person argues that his opponent ought to accept the truth of an assertion because of the opponent's particular circumstances. For example: "It is perfectly acceptable to kill animals for food. How can you argue otherwise when you're quite happy to wear leather shoes?" This is an abusive charge of inconsistency, used as an excuse for dismissing the opponent's argument. This fallacy can also be used as a means of rejecting a conclusion. For example: "Of course you would argue that positive discrimination is a bad thing. You're white." This particular form of Argumentum ad Hominem, when one alleges that one's adversary is rationalizing a conclusion formed from selfish interests, is also known as "poisoning the well". ARGUMENTUM AD IGNORANTIAM Argumentum ad ignorantiam means "argument from ignorance". This fallacy occurs whenever it is argued that something must be true simply because it has not been proved false. Or, equivalently, when it is argued that something must be false because it has not been proved true. (Note that this is not the same as assuming that something is false until it has been proved true, a basic scientific principle.) Examples: "Of course the Bible is true. Nobody can prove otherwise." "Of course telepathy and other psychic phenomena do not exist. Nobody has shown any proof that they are real." Note that this fallacy does not apply in a court of law, where one is generally assumed innocent until proven guilty. Also, in scientific investigation if it is known that an event would produce certain evidence of its having occurred, the absence of such evidence can validly be used to infer that the event did not occur. For example: "A flood as described in the Bible would require an enormous volume of water to be present on the earth. The earth does not have a third as much water, even if we count that which is frozen into ice at the poles. Therefore no such flood occurred." In science, we can validly assume from lack of evidence that something has not occurred. We cannot conclude with certainty that it has not occurred, however. See also Shifting the Burden of Proof Argumentum ad Ignorantium: "Arguing something is true because it hasn't been proven false, _or_, arguing something is false because it hasn't been proven true. Either case is a logical fallacy, an appeal to ignorance." The argumentum ad ignorantium is committed whenever 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. But our ignorance of how to prove or disprove a proposition clearly does not establish either the truth of the falsehood of that proposition." - Irving M.Copi from "Introduction to Logic" 7th edition, (MacMillan Press, New York, 1986), page 94 Famous in the history of science is the argument _ad ignorantium_ 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. And this hypothesis, which saves the perfection of the heavenly bodies, Galileo could not prove false! (Copi and Cohen, _Introduction to Logic_, p. 117) Galileo answered that there might be vast crystaline mountains there, invisible to the eye. This could not be proved false either. ARGUMENTUM AD MISERICORDIAM This is the Appeal to Pity, also known as Special Pleading. The fallacy is committed when the arguer appeals to pity for the sake of getting a conclusion accepted. For example: "I did not murder my mother and father with an axe. Please don't find me guilty; I'm suffering enough through being an orphan." Description of Special Pleading Special Pleading is a fallacy in which a person applies standards, principles, rules, etc. to others while taking herself (or those she has a special interest in) to be exempt, without providing adequate justification for the exemption. The person committing Special Pleading is claiming that he is exempt from certain principles or standards yet he provides no good reason for his exemption. In your case, God is exempt from any standard for evaluating good, merciful, or holy behavior because he is God. You advertise and make claims that you never have to establish through evidence. In your world, simply making the claim God is holy makes God holy. Then you tell people who don't accept your unsupported claim that they are insecure or lack understanding. ARGUMENTUM AD POPULUM This is known as Appealing to the Gallery, or Appealing to the People. To commit this fallacy is to attempt to win acceptance of an assertion by appealing to a large group of people. This form of fallacy is often characterized by emotive language. For example: "Pornography must be banned. It is violence against women." "The Bible must be true. Millions of people know that it is. Are you trying to tell them that they are all mistaken fools?" ARGUMENTUM AD NUMERUM This fallacy is closely related to the argumentum ad populum. It consists of asserting that the more people who support or believe a proposition, the more likely it is that that proposition is correct. ARGUMENTUM AD VERECUNDIAM The Appeal to Authority uses the admiration of the famous to try and win support for an assertion. For example: "Isaac Newton was a genius and he believed in God." This line of argument is not always completely bogus; for example, reference to an admitted authority in a particular field may be relevant to a discussion of that subject. For example, we can distinguish quite clearly between: "Hawking has concluded that black holes give off radiation" and "Penrose has concluded that it is impossible to build an intelligent computer" Hawking is a physicist, and so we can reasonably expect his opinions on black hole radiation to be informed. Penrose is a mathematician, so it is questionable whether he is well-qualified to speak on the subject of machine intelligence. THE FALLACY OF ACCIDENT The Fallacy of Accident is committed when a general rule is applied to a particular case whose "accidental" circumstances mean that the rule is inapplicable. It is the error made when one goes from the general to the specific. For example: "Christians generally dislike atheists. You are a Christian, so you must dislike atheists." This fallacy is often committed by moralists and legalists who try to decide every moral and legal question by mechanically applying general rules. CONVERSE ACCIDENT / HASTY GENERALIZATION This fallacy is the reverse of the Fallacy of Accident. It occurs when one forms a general rule by examining only a few specific cases which are not representative of all possible cases. For example: "Jim Bakker was an insincere Christian. Therefore all Christians are insincere." SWEEPING GENERALIZATION / DICTO SIMPLICITER A sweeping generalization occurs when a general rule is applied to a particular situation in which the features of that particular situation render the rule inapplicable. A sweeping generalization is the opposite of a hasty generalization. NON CAUSA PRO CAUSA / POST HOC ERGO PROPTER HOC These are known as False Cause fallacies. The fallacy of Non Causa Pro Causa occurs when one identifies something as the cause of an event but it has not actually been shown to be the cause. For example: "I took an aspirin and prayed to God, and my headache disappeared. So God cured me of the headache." The fallacy of Post Hoc Ergo Propter Hoc occurs when something is assumed to be the cause of an event merely because it happened before the event. For example: "The Soviet Union collapsed after taking up atheism. Therefore we must avoid atheism for the same reasons." CUM HOC ERGO PROPTER HOC This fallacy is similar to Post Hoc Ergo Propter Hoc. It asserts that because two events occur together, they must be causally related, and leaves no room for other factors that may be the cause(s) of the events. PETITIO PRINCIPII / BEGGING THE QUESTION This fallacy occurs when the premises are at least as questionable as the conclusion reached. CIRCULUS IN DEMONSTRANDO This fallacy occurs when one assumes as a premise the conclusion which one wishes to reach. Often, the proposition will be rephrased so that the fallacy appears to be a valid argument. For example: "Homosexuals must not be allowed to hold government office. Hence any government official who is revealed to be a homosexual will lose his job. Therefore homosexuals will do anything to hide their secret, and will be open to blackmail. Therefore homosexuals cannot be allowed to hold government office." Note that the argument is entirely circular; the premise is the same as the conclusion. An argument like the above has actually been cited as the reason for the British Secret Services' official ban on homosexual employees. Another example is the classic: "We know that God exists because the Bible tells us so. And we know that the Bible is true because it is the word of God." COMPLEX QUESTION / FALLACY OF INTERROGATION / FALLACY OF PRESUPPOSITION This is the interrogative form of Begging the Question. One example is the classic loaded question: "Have you stopped beating your wife?" The question presupposes a definite answer to another question which has not even been asked. This trick is often used by lawyers in cross-examination, when they ask questions like: "Where did you hide the money you stole?" Similarly, politicians often ask loaded questions such as: "How long will this EC interference in our affairs be allowed to continue?" or "Does the Chancellor plan two more years of ruinous privatization?" Another form of this fallacy is to ask for an explanation of something which is untrue or not yet established. IGNORATIO ELENCHI The fallacy of Irrelevant Conclusion consists of claiming that an argument supports a particular conclusion when it is actually logically nothing to do with that conclusion. For example, a Christian may begin by saying that he will argue that the teachings of Christianity are undoubtably true. If he then argues at length that Christianity is of great help to many people, no matter how well he argues he will not have shown that Christian teachings are true. Sadly, such fallacious arguments are often successful because they arouse emotions which cause others to view the supposed conclusion in a more favourable light. EQUIVOCATION / FALLACY OF FOUR TERMS Equivocation occurs when a key word is used with two or more different meanings in the same argument. For example: "What could be more affordable than free software? But to make sure that it remains free, that users can do what they like with it, we must place a license on it to make sure that will always be freely redistributable." AMPHIBOLY Amphiboly occurs when the premises used in an argument are ambiguous because of careless or ungrammatical phrasing. ACCENT Accent is another form of fallacy through shifting meaning. In this case, the meaning is changed by altering which parts of a statement are emphasized. For example, consider: "We should not SPEAK ill of our friends" and "We should not speak ill of our FRIENDS" Circulus in demonstrando This fallacy occurs when one assumes as a premise the conclusion which one wishes to reach. Often, the proposition will be rephrased so that the fallacy appears to be a valid argument. FALLACIES OF COMPOSITION One Fallacy of Composition is to conclude that a property shared by the parts of something must apply to the whole. For example: "The bicycle is made entirely of low mass components, and is therefore very lightweight." The other Fallacy of Composition is to conclude that a property of a number of individual items is shared by a collection of those items. For example: "A car uses less petrol and causes less pollution than a bus. Therefore cars are less environmentally damaging than buses." FALLACY OF DIVISION The fallacy of division is the opposite of the Fallacy of Composition. Like its opposite, it exists in two varieties. The first is to assume that a property of some thing must apply to its parts. For example: "You are studying at a rich college. Therefore you must be rich." The other is to assume that a property of a collection of items is shared by each item. For example: "Ants can destroy a tree. Therefore this ant can destroy a tree." THE SLIPPERY SLOPE ARGUMENT This argument states that should one event occur, so will other harmful events. There is no proof made that the harmful events are caused by the first event. For example: "If we legalize marijuana, then we would have to legalize crack and heroin and we'll have a nation full of drug-addicts on welfare. Therefore we cannot legalize marijuana." "A IS BASED ON B" FALLACIES / "...IS A TYPE OF..." FALLACIES / FALLACY OF THE UNDISTRIBUTED MIDDLE These fallacies occur when one attempts to argue that things are in some way similar without actually specifying in what way they are similar. Examples: "Isn't history based upon faith? If so, then isn't the Bible also a form of history?" "Islam is based on faith, Christianity is based on faith, so isn't Islam a form of Christianity?" "Cats are a form of animal based on carbon chemistry, dogs are a form of animal based on carbon chemistry, so aren't dogs a form of cat?" AFFIRMATION OF THE CONSEQUENT This fallacy is an argument of the form "A implies B, B is true, therefore A is true". To understand why it is a fallacy, examine the truth table for implication given earlier. DENIAL OF THE ANTECEDENT This fallacy is an argument of the form "A implies B, A is false, therefore B is false". The truth table for implication makes it clear why this is a fallacy. Note that this fallacy is different from Non Causa Pro Causa. The latter has the form "A implies B, A is false, therefore B is false", where A does not in fact imply B at all. Here, the problem is not that the implication is invalid; rather it is that the falseness of A does not allow us to deduce anything about B. CONVERTING A CONDITIONAL This fallacy is an argument of the form "If A then B, therefore if B then A". ARGUMENTUM AD ANTIQUITATEM This is the fallacy of asserting that something is right or good simply because it is old, or because "that's the way it's always been." ARGUMENTUM AD NOVITATEM This is the opposite of the Argumentum ad Antiquitatem; it is the fallacy of asserting that something is more correct simply because it is new or newer than something else. ARGUMENTUM AD CRUMENAM The fallacy of believing that money is a criterion of correctness; that those with more money are more likely to be right. ARGUMENTUM AD LAZARUM The fallacy of assuming that because someone is poor he or she is sounder or more virtuous than one who is wealthier. This fallacy is the opposite of the argumentum ad crumenam. ARGUMENTUM AD NAUSEAM This is the incorrect belief that an assertion is more likely to be true the more often it is heard. An "argumentum ad nauseam" is one that employs constant repetition in asserting something. BIFURCATION Also referred to as the "black and white" fallacy, bifurcation occurs when one presents a situation as having only two alternatives, where in fact other alternatives exist or can exist. PLURIUM INTERROGATIONUM / MANY QUESTIONS This fallacy occurs when a questioner demands a simple answer to a complex question. NON SEQUITUR A non-sequitur is an argument where the conclusion is drawn from premises which are not logically connected with it. Example 1+1=2 The whole is greater than the part. Therefore, God is love. RED HERRING This fallacy is committed when irrelevant material is introduced to the issue being discussed, so that everyone's attention is diverted away from the points being made, towards a different conclusion. REIFICATION / HYPOSTATIZATION Reification occurs when an abstract concept is treated as a concrete thing. SHIFTING THE BURDEN OF PROOF The burden of proof is always on the person making an assertion or proposition. Shifting the burden of proof, a special case of Argumentum ad Ignorantiam, is the fallacy of putting the burden of proof on the person who denies or questions the assertion being made. The source of the fallacy is the assumption that something is true unless proven otherwise. For further discussion of this idea, see the "Introduction to Atheism" document. STRAW MAN The straw man fallacy is to misrepresent someone else's position so that it can be attacked more easily, then to knock down that misrepresented position, then to conclude that the original position has been demolished. It is a fallacy because it fails to deal with the actual arguments that have been made. THE EXTENDED ANALOGY The fallacy of the Extended Analogy often occurs when some suggested general rule is being argued over. The fallacy is to assume that mentioning two different situations, in an argument about a general rule, constitutes a claim that those situations are analogous to each other. This fallacy is best explained using a real example from a debate about anti-cryptography legislation: "I believe it is always wrong to oppose the law by breaking it." "Such a position is odious: it implies that you would not have supported Martin Luther King." "Are you saying that cryptography legislation is as important as the struggle for Black liberation? How dare you!" TU QUOQUE This is the famous "you too" fallacy. It occurs when an action is argued to be acceptable because the other party has performed it. For instance: "You're just being randomly abusive." "So? You've been abusive too." This is a personal attack, and is therefore a special case of Argumentum ad Hominem. AUDIATUR ET ALTERA PARS Often, people will argue from assumptions which they do not bother to state. The principle of Audiatur et Altera Pars is that all of the premises of an argument should be stated explicitly. It is not strictly a fallacy to fail to state all of one's assumptions; however, it is often viewed with suspicion. AD HOC There is a difference between argument and explanation. If we're interested in establishing A, and B is offered as evidence, the statement "A because B" is an argument. If we're trying to establish the truth of B, then "A because B" is not an argument, it is an explanation. The Ad Hoc fallacy is to give an after-the-fact explanation which does not apply to other situations. Often this ad hoc explanation will be dressed up to look like an argument. For example, if we assume that God treats all people equally, then the following is an ad hoc explanation: "I was healed from cancer." "Praise the Lord, then. He is your healer." "So, will He heal others who have cancer?" "Er... The ways of God are mysterious." ARGUMENTUM AD LOGICAM This is the "fallacy fallacy" of arguing that a proposition is false merely on the grounds that it has been presented as the conclusion of a fallacious argument. Remember always that fallacious arguments can arrive at true conclusions. When a fallacy is used in an argument that doesn't imply the conclusion is wrong. It only means the argument doesn't support the conclusion. === ARGUMENTUM AD CONSEQENTIAM The social and political consequences of a theory if it were true, have no bearing on whether or not it is true. === => Implies Modus ponens If A and A=>B then B Modus tollens If B is false and A=>B then A is false === Ockahm's Principle Pluralitas non est ponenda sine neccesitate\ (plurality should not be posited without necessity) or Frustra fit per plura quod potest fieri per pauciora (It is futile to do with more what can be done with fewer). or Quando propositio verificatur pro rebus, si duae res sufficiunt ad eius veritatem, superfluum est ponere tertiam. (When a proposition comes out true for things, if two things suffice for its truth, it is superfluous to assume a third.) or Nulla pluralitas est ponenda nisi per rationem vel experientiam vel auctoritatem illius, qui non potest falli necerrare, potest convinci. (\No plurality should be assumed unless it can be proved (a) by reason, or (b) by experience, or (c) by some infallible authority.) The commonly quoted Entities should not be multiplied unnecessarily is a translation of Entia non sunt multiplicanda praeter necessitatem which does not actually appear in Occam's extant writings. == Fallacy: Argumentum ad Populum Alternate Names: Appeal to the People Appeal to the Majority Appeal to the Gallery Appeal to Popular Prejudcie Appeal to the Mob Appeal to the Multitude Argument from Consensus Argumentum ad Numerum Explanation: This fallacy occurs any time the sheer numbers of people who agree to something is used as a reason to get you to agree to it and takes the general form: 1. When most people agree on a claim about subject S, the claim is true (normally an unstated premise). Claim X is one which most people agree on. Therefore, X is true. This fallacy can take on the direct approach, where a speaker is addressing a crowd and makes a deliberate attempt to excite their emotions and passions in an attempt to get them to accept what he is saying. What we see here is the development of a sort of \mob mentality\ - people go along with what they hear because they experience others also going along with it. This is, obviously enough, a common tactic in political speeches. This fallacy can also take on an indirect approach, where the speaker is, or seems to be, addressing a single person while focusing on some relationship that individual has to larger groups or crowds. Examples and Discussion: One common way this fallacy is used is known as the \Bandwagon Argument.\ Here, the arguer explicitly relies upon people's desire to fit in and be liked by others to get them to \go along\ with the offered conclusion. Naturally, it is a common tactic in advertising: 2. Our cleaner is preferred two-to-one over the next leading brand. 3. The number one movie for three weeks in a row! 4. This book has been on the New York Times' bestseller list for 64 straight weeks. 5. Over four million people have switched to our insurance company - shouldn't you In all of the above cases, you are being told that lots and lots of other people prefer some particular product. In example #2, you are even being told to what degree it is allegedly preferred over the nearest competitor. Example #5 makes an overt appeal to you to follow the crowd, and with the others this appeal is implied. We also find this argument used in religion: 6. Hundreds of millions of people have been Christians, devoutly following it and even dying for it. How could that be possible if Christianity weren't true? Once again, we find the argument that the number of people who accept a claim is a good basis for believing that claim. But we know now that such an appeal is fallacious - hundreds of millions of people can be wrong. == I.M. Copi and Cohen, _Introduction to Logic 7th edition, (MacMillan Press, New York, 1986) Ayer *Language, Truth, and Logic* http://www.virtualschool.edu/mon/SocialConstruction/Logic.html http://www.pleasurepoint.com/logical.html great logic reference http://www.aros.net/~wenglund/Logic101a.htm http://www.virtualschool.edu/mon/SocialConstruction/Logic.html http://structuredindividuals.com/index.html Advanced Logic http://structuredindividuals.com/paradox/9.html http://www.drury.edu/faculty/Ess/critthink.html http://www3.nd.edu/~afreddos/courses/301/presocs.htm http://pnarae.com/phil/category/logic/LogiDagl.htm http://www.csc.tntech.edu/~srini/DM/chapters/review1.1.html http://www.nizkor.org/features/fallacies/ad-hominem.html http://www.nizkor.org/features/fallacies/ad-hominem-tu-quoque.html http://www.intrepidsoftware.com/fallacy/begging.htm http://www.nizkor.org/features/fallacies/straw-man.html http://www.nizkor.net/features/fallacies/appeal-to-consequences.html http://plato.stanford.edu/entries/logic-informal/ http://www.infidels.org/news/atheism/logic.html http://www.cuyamaca.net/bruce.thompson/Fallacies/ignoratio.asp http://www.cuyamaca.net/bruce.thompson/Fallacies/diversion.asp http://www.nizkor.org/features/fallacies/ http://www.aros.net/~wenglund/Logic101a.htm http://www.don-lindsay-archive.org/skeptic/arguments.html http://www.intrepidsoftware.com/fallacy/toc.php http://philosophy.lander.edu/logic/ http://www.infidels.org/news/atheism/logic.html http://www.datanation.com/fallacies/index.htm END A21-Logic.txt