Here are some examples of common fallacies:
ad hominemA theory is discarded not because of any evidence against it or lack of evidence for it, but because of the person who argues for it. Example:
- A: The Government should enact minimum-wage legislation so that workers are not exploited.
B: Nonsense. You say that only because you cannot find a good job.
ad ignorantiam (appeal to ignorance)The truth of a claim is established only on the basis of lack of evidence against it. A simple obvious example of such fallacy is to argue that unicorns exist because there is no evidence against such a claim. At first sight it seems that many theories that we describe as scientific involve such a fallacy. E.g. the first law of thermodynamics holds because so far there has not been any negative instance that would serve as evidence against it. But notice, as in cases like this, there is evidence for the law, namely positive instances. Notice also that this fallacy does not apply to situations where there are only two rival claims and one has already been falsified, then we may justly establish the truth of the other even if we cannot find evidence for or against it.
ad misericordiam (appeal to pity)In offering an argument, pity is appealed to. Usually this happens when people argue for special treatment on the basis of their need. E.g. a student argues that the teacher should let him/her pass the examination because he/she needs it in order to graduate. Of course, pity might be a relevant consideration in certain conditions, as in contexts involving charity.
ad populum (appeal to popularity)The truth of a claim is established only on the basis of its popularity and familiarity. This is the fallacy committed by many commercials. Surely you have heard of commercials implying that we should buy a certain product because it has made to the top of a sales rank, or because the brand is the city's "favourite".
Affirming the consequent
Inferring that P is true solely because Q is true and it is also true that if P is true, Q is true.
The problem with this type of reasoning is that it ignores the possibility that there are other conditions apart from P that might lead to Q. For example, if there is a traffic jam, a colleague may be late for work. But if we argue from his being late to there being a traffic jam, we are guilty of this fallacy - the colleague may be late due to a faulty alarm clock.
Of course, if we have evidence showing that P is the only or most likely condition that leads to Q, then we can infer that P is likely to be true without committing a fallacy.
Begging the question (petito principii)In arguing for a claim, the claim itself is already assumed in the premise. Example: "God exists because this is what the Bible says, and the Bible is reliable because it is the word of God."
Complex question or loaded question
A question is posed in such a way that a person, no matter what answer he/she gives to the question, will inevitably commit him/herself to some other claim, which should not be presupposed in the context in question.
A common tactic is to ask a yes-no question that tricks people to agree to something they never intended to say. For example, if you are asked "Are you still as self-centred as you used to be?", then no matter you answer "yes" or "no", you are bound to admit that you were self-centred in the past. Of course, the same question would not count as a fallacy if the presupposition of the question is indeed accepted in the conversational context.
Composition (opposite of division)The whole is assumed to have the same properties as its parts. Anne might be humorous and fun-loving and an excellent person to invite to the party. The same might be true of Ben, Chris and David considered individually. But it does not follow that it will be a good idea to invite all of them to the party. Perhaps they hate each other and the party will be ruined.
Denying the antecedent
Inferring that Q is false just because if P is true, Q is also true, but P is false.
This fallacy is similar to the fallacy of affirming the consequent. Again the problem is that some alternative explanation or cause might be overlooked. Although P is false, some other condition might be sufficient to make Q true.
Example: If there is a traffic jam, a colleague may be late for work. But it is not right to argue in the light of a smooth traffic that the colleague will not be late. Again, his alarm clock may have stopped working.
Division (opposite of composition)The parts of a whole is assumed to have the same properties of the whole. It is possible that, on a whole, a company is very effective, while some of its departments are not. It would be inappropriate to assume they all are.
EquivocationPutting forward an argument where a word changes meaning without having it pointed out. For example, some philosophers argue that all acts are selfish. Even if you strive to serve others, you are still acting selfishly because your act is just to satisfy your desire to serve others. But surely the word "selfish" means differently in the premise and the conclusion - when we say a person is selfish we usually mean that he does not strive to serve others. To say that a person is selfish because he is doing something he wants, even when what he wants is to help others, is to use the term "selfish" with a different meaning.
False dilemmaPresenting a limited set of alternatives when there are others that are worth considering in the context. Example: "Every person is either my enemy or my friend. If he/she is my enemy I should hate him/her. If he/she is my friend I should love him/her. So I should either love him/her or hate him/her." Obviously, the conclusion is too extreme because most people are neither your enemy nor your friend.
Gambler's fallacyAssumption is made to take some independent statistics as dependent. The untrained mind tends to think that, e.g. if a fair coin is tossed five times and the results are all heads, then the next toss will more likely be a tail. It will not be, however. If the coin is fair, the result for each toss is completely independent of the others. Notice the fallacy hinges on the fact that the final result is not known. Had the final result been known already, the statistics would have been dependent.
Genetic fallacyThinking that because X dervies from Y, and Y has a certain property, X must have the same property also. Example: "His father is a criminal, so he must also be up to no good."
Non sequiturA conclusion is drawn which does not follow from the premise. This is not a specific fallacy but a very general term for a bad argument. So a lot of the examples above and below can be said to be non sequitur.
Petito principiiLatin word for question begging.
Post hoc, ergo propter hoc (literally, "after this, therefore because of this")
Inferring that X must be the cause of Y just because X is followed by Y.
For example, having visited a graveyard, I fell ill and infer that graveyards are spooky places that cause illnesses. Of course, this inference is not warranted since this might just be a coincidence. However, a lot of superstituous beliefs commit this fallacy.
Within an argument some irrelevant issue is raised which diverts attention from the main subject. The function of the red herring is sometimes to help express a strong, biased opinion. The red herring (the irrelevant issue) serves to increase the force of the argument in a very misleading manner.
For example, in a debate as to whether God exists, someone might argue that believing in God gives peace and meaning to many people's lives. This would be an example of a red herring since whether religions can have a positive effect on people is irrelevant to the question of the existence of God. The good psychological effect of a belief is not a reason for thinking that the belief is true.
Arguing that if an opponent were to accept some claim C1, then he or she has to accept some other closely related claim C2, which in turn commits the opponent to a still further claim C3, eventually leading to the conclusion that the opponent is committed to something absurd or obviously unacceptable.
This style of argumentation constitutes a fallacy only when it is inappropriate to think if one were to accept the initial claim, one must accept all the other claims.
An example: "The government should not prohibit drugs. Otherwise the government should also ban alcohol or cigarettes. And then fatty food and junk food would have to be regulated too. The next thing you know, the government would force us to brush our teeth and do exercises everyday."
Attacking an opponent by attributing to him/her an implausible position that is easily defeated when this is not actually the opponent's position.
Example: When many people argue for more democracy in Hong Kong, a typical reply is to say that this is not warranted because it is wrong to think that democracy is the solution to all of Hong Kong's problems, or to say that one should not blindly accept democracy. But those who support democracy never suggest that democracy can solve all problems (e.g. pollution), and they might also agree that blindly accepting something is rarely correct, whether it is democracy or not. Those criticisms attack implausible "strawman" positions and do not address the real arguments for democracy.
Where there is contradicting evidence, only confirming evidence is presented.
previous tutorial next tutorial
Three Critical Questions
The goals of rational criticism can be formulated by three more or less distinct questions.
(1) Is the reasoning well-formulated?
(2) Is the reasoning well-connected?
(3) Is the reasoning well-established?
Questions of formulation relate to the attempt to understand exactly what the person is saying and the background against which he or she is saying it. It is here that we sometimes find that a person has gotten off on the wrong foot by misrepresenting a person's views, or conflating different kinds of statements, or misconstruing the nature of the problem at issue.
Questions of connection relate to the attempt to understand how what a person is saying is relevant to the conclusion s/he appears to be drawing. It is here that we sometimes find that a person has said things that are logically irrelevant to the question at issue, but which might nevertheless persuade people on non logical grounds (e.g. by confusing them, or appealing to their emotions or self-interest.)
The question whether a person's reasoning is well-established raises issues of confirmation and credibility. It is here that we sometimes find that the reasoning being offered rests on weak principles or reasons that have not been adequately supported.
What Is a Fallacy?
Some errors in reasoning are simply the result of the fact that people aren't perfect. Sometimes we hit the wrong letter on the keyboard, sometimes we get on the wrong bus, sometimes we swing at the ball and miss, and sometimes we draw the wrong conclusion. Stuff like this just happens. Sometimes, however, our errors are the result of a fundamental problem that will cause us to repeat the same mistakes over and over. E.g., you may not know how to type; you may not understand how to read the bus schedule, or you may have a bad batting stance. In logic, mistakes due to some fundamental problem are called fallacies. A fallacy is a systematic error, as opposed to a random error. We usually say that fallacies are a systematic error in reasoning , which is true, but only if you understand reasoning very broadly as the process of formulating, connecting, and establishing the reasons for your conclusions. (Some people think of reasoning as just the process of connecting reasons to conclusions, and only some of the fallacies relate to this.) We are going to begin developing the tools of rational criticism by discussing some basic fallacies relevant to the categories introduced above. Later on we will discuss more specific sorts of fallacies and other problems that are not simple enough to be defined as fallacies at all.
Two Fallacies of Formulation: Straw Person, False Alternatives
Two of the most common mistakes people make in formulating their reasoning are: (1) misrepresenting views they want to refute; (2) misrepresenting the nature of the problem they are addressing. The first mistake is traditionally called the Straw Person Fallacy. An important form of the second mistake is called False Alternatives (or False Dilemma).
Def.: Attempting to discredit a view by criticizing a weak version of it or the reason given in support of it.
The idea behind Straw Person is that if you can get people to think that a "straw" version (think of a scarecrow) of what a person is saying is the real version, then you can appear to be refuting what the person has said without actually addressing it at all. This sounds like it takes a lot of cunning and deceit, but the fact is that we all do it spontaneously. It takes a great deal of discipline and intellectual honesty to listen carefully to what someone is saying and represent it accurately before going on to criticize it. If you feel from the beginning that a person is wrong, you will naturally think that it isn't worth your time to listen very carefully to what they are saying.
E.g. 1: Barb feels ill one morning and asks Butch to inform the instructor that this is the reason why she will not be in class. Butch carries out Barb's request as follows: "Barb isn't here today because she didn't feel like coming." Obviously, Barb would not be happy with this version of her absence because Butch has stated in a way that is easy to criticize. Now it sounds more like an unexcused absence than an excused one.
E.g. 2.: Butch claims that, generally speaking, women are far more concerned about their personal appearances than men, pointing out that most make-up is sold to women and that popular women's clothing is often very uncomfortable, but women buy it because it is attractive to men.. Barb replies: "That's totally ridiculous, not all women wear that kind of stuff and lots of men are using make-up these days, too." This is a straw person because Butch didn't make a claim about all women or men. Understood in this way, Butch's statements are obviously false.
E.g 3: Butch is beside himself with anger because the construction workers across the street have been shouting lewd comments at him all week. Barbs says, "Well, if you don't like it maybe you should stop running around in your Speedo." Butch responds, "That is just so unfair! I have a right to be comfortable in my own yard." Here, Butch has interpreted Barb's remark as an implicit criticism of his Speedo outfit, rather than simply a piece of advise about how to avoid being teased. (This example has an interesting connection to Innunendo.)
E.g. 4: A defense attorney argues that, even though expert testimony has established that the defendant knew that she was breaking the law when she bombed the abortion clinic, she should be found not guilty by reason of insanity. The attorney reminds the jury that a person is legally insane when they do not know the difference between right and wrong. The fact that she knew the difference between what is legal and illegal does not mean she knew the difference between right and wrong, for the two issues are distinct. If it were always wrong to do things that are illegal, then civil disobedience (disobeying the law for a higher moral cause) would be impossible. The prosecuting attorney responds to this line of reasoning as follows: "The defense has asked us to find the defendant not guilty on the grounds that bombing an abortion clinic is essentially like an act of civil disobedience. It is difficult to think of anything more preposterous than to compare this act of sheer violence with peaceful acts of civil disobedience." Again, in this example, the defense attorney would object to the prosecutions characterization of her reasoning. This version does sound preposterous, though the original reasoning was not.
Def.: Misformulating a problem as a choice between two (or more) alternatives, when there exist other alternatives that have not been considered.
False Alternatives is essentially a problem of oversimplification. Its usual form is: "You have a choice between A and B. A is obviously unacceptable, therefore you must do B." This is actually a perfectly acceptable form of inference known as the Disjunctive Syllogism. The problem is that the choice itself may be misrepresented; i.e., the real choice might be between A, B, C &D. Also, sometimes more than one option can be available to you at the same time. It is worth pointing out that choices are not always expressed as "Either...or." Sometimes people will say "If you don't do B, then A is going to happen." If you think about it, you'll see that this is just another way of saying that you have a choice between A and B.
E.g. 1: "I don't want to hear anything more about your mother being black and your father being white. Sooner or later you are going to have to admit that you are a black man and accept the responsibilities that go along with that." A statement like this rests on characterizing the problem of understanding ones true nature as a choice between two simple alternatives, black and non black. It does not allow that a person may regard neither category as an accurate reflection of who they are.
E.g. 2: In response to the problem of illegal immigration from Mexico someone might argue that the only way to deal with the problem of illegal immigration is to massively increase our border controls, and vigorously pursue and deport all illegal aliens. This characterizes the situation as a choice between two alternatives; viz., increased law enforcement or an unacceptably high level of illegal immigrants. However, these may not be the only alternatives. For example, one might suggest that the problem would be better addressed by increasing trade with Mexico, thereby improving the economy and reducing people's incentive to immigrate.
Two Fallacies of Connection: Red Herring, Ad Hominem
Under certain situations it is possible to say things that are logically irrelevant to the issue at hand, but which nevertheless succeed in having some effect on the way in which people understand it. There are two standard ways of doing this. (1) Introduce an issue that is superficially similar to the one being discussed; (2) Focus attention on the speaker rather than what the speaker is saying. The first of these fallacies is called Red Herring. The second is called Ad Hominem. (These, by the way, are not totally distinct fallacies; technically, an Ad Hominem is a Red Herring.)
Def.: Distracting attention from an issue by introducing an irrelevant issue or one that is only superficially related to the one being discussed. The mechanism of this fallacy is similar to that of Straw Person. Both depend on creating something that has a deceptive resemblance to the genuine article. Also, like Straw Person, Red Herring does not depend on intentionally deceiving someone. More often than not people commit Red Herring because they don't know or can't keep their minds focused on the real issue.
E.g. 1: Suppose people in our community are drawing graffiti on public buildings. I point out that it is an illegal activity and suggest that we should make a more concerted effort to apprehend and prosecute the offenders. You respond as follows: "But graffiti is art and the people who do it are artists." This is a Red Herring, because the artistic value of graffiti is unrelated to the question of its legality. However, because you are still talking about graffiti and saying something that I might disagree with, you may succeed in distracting my attention from the real issue.
E.g., 2: Suppose I claim that homosexuality is a disease and that the proper approach is to try to cure it rather than to integrate it into our society. To this you respond "That's outrageous. People don't choose to be homosexuals, they are born that way." This, too, may succeed in distracting me from my point, but it is irrelevant to the question whether homosexuality is a disease. Many people are born with diseases.
E.g., 3: Suppose we are members of a jury trying to determine whether the evidence we have just heard is sufficient to convict the defendant of robbing a bank. In his defense, you point out that the defendant is destitute, that his family was hungry, and that he was wrongly fired from his previous job. This is a specific kind of Red Herring called Appeal to Emotion. What you have said is irrelevant to the question whether he committed the crime, but it may influence the decision by making us feel sorry for him.
Def.: Any attempt to discredit a view by calling attention to the character, actions or personal circumstances of those who hold it rather than the reasoning they provide in support of it.
"Ad hominem" is Latin for "against the person." Anything that involves an attack on a person's character we call an Abusive Ad Hominem. Anything that appeals to a person's unique circumstances we call a Circumstantial ad Hominem. These are both fallacious for the simple reason that the personal character and circumstances of the individual reasoner are logically irrelevant to the question whether the reasoning itself is any good.
E.g. 1: Suppose a very rich person like Ross Perot gives a speech in which he argues that it is not such a great thing to be rich and that, in fact, people who are poor are likely to live better lives on the whole. Of course, we want to respond: "Oh, sure, that's easy for you to say, but I don't see you giving away all your money." This is an abusive Ad Hominem, because we are attacking Perot as a hypocrite rather than examining the argument itself. It is also known at the fallacy of Tu Quoque, which is Latin for "You do it, too."
E.g. 2: Suppose I am a member of an ethnic minority and I am arguing against affirmative action. You may be inclined to give me the following advice: "You are foolish to adopt this view. Don't you realize that as a member of an ethnic minority you stand to benefit from affirmative actions programs?" This is a Circumstantial Ad Hominem because you are using my personal circumstances in order to try to discredit my view or encourage me to adopt a different one. You do not actually examine the reasoning I have produced.
Two Fallacies of Establishment: Appeal to Questionable Authority and Questionable Analogy
There are many ways to make it seem as if our claims are more credible than they actually are. Two of the most common are: (1) Appealing to a questionable source of authoritative information; (2) Making superficial comparisons. The first of these is called Appeal to Questionable Authority. The second is called Questionable Analogy.
Appeal to Questionable Authority
Def.: Accepting or recommending a claim on the basis of an appeal to an authoritative source of information when there are reasons for doubting the source in question. This fallacy has many forms. We sometimes make inappropriate appeals to the authority of common opinion and tradition. We also sometimes appeal to individual organizations and people as authoritative sources even though we are uncertain who they are, what their claim to authority is, or whether they should be trusted. Questionable authority is a fallacy that is often misused, however, as our first example shows.
E.g. 1: Suppose you explain to me why the Federal Reserve Board is going to raise interest rates. You tell me that the Feds are concerned about rising inflation, and that raising interest rates tend to reduce consume borrowing, which reduces consumer demand, which reduces the amount that manufacturers can charge for their products, which reduces inflation. Now, suppose I respond as follows: "Are you some sort of authority on economics or something? Why should I listen to you?" Now, this would not be a legitimate thing for me to say. You never claimed to be an authority. You gave me some reasoning and I have ignored it, preferring to talk about your personal qualifications instead. In fact, I have just committed an Abusive Ad Hominem. The moral of this example is: An appeal to Questionable Authority occurs only when somebody uses authority in order to legitimate something they say. If they do not use authority, then it is illegitimate to raise the issue.
E.g. 2: Suppose I own a music store and am also an accomplished musician on several instruments. I sell pianos but no string instruments like guitars or cellos. You ask me what's the best instrument to start out learning on and I say, unequivocally, a piano. When you ask me why, I say that you can trust me on this. I play all sorts of instruments and the piano is by far the best one to start out on. In fact, I explain, that's why I only sell pianos. Notice that in this situation I haven't given you a single reason for believing the piano is the best instrument to learn on except my authority. But, knowing that my livelihood depends on the sale of pianos, it would be wrong to accept my appeal to authority. I have what is commonly called a "conflict of interest."
E.g. 3: Suppose the issue is whether we should allow prayer in public schools. You argue that we should because disallowing prayer is a violation of religious freedom, and that individual freedom is what the United States stands for. I say we should not because everybody who understands the Constitution realizes that the separation of church and state is fundamental. I have made an appeal to Questionable Authority because the sole reason I give is that "everybody who understands the Constitution" agrees with me. I have not identified who these people are. Also I have made an appeal to the Constitution as a kind of time-honored document that should not be tampered with. This an appeal to the authority of tradition. I haven't given any actual reason for thinking the Constitution can not be amended which, of course, it can.
Def.: Any reasoning based on the assumption that two or more things that are alike in one respect must be alike in other respects when there are independent grounds for doubting this. We draw an analogy whenever we claim that two different things are similar in significant respects. However, sometimes we draw an analogy when there is, in fact, an important difference that may undermine the conclusion the analogy is meant to support. For example, it would be ridiculous for me to say "Gina and Lisa are both girls. Gina is five feet tall, so I guess Lisa is probably five feet tall, too." Here, you would want to point out that there is no principle that say "If X is a girl, then X is five feet tall." Another way of making this point is to accuse me of a questionable analogy by observing that just because Gina and Lisa are similar in one physical respect (viz., sex) doesn't mean they are similar in other physical respects (viz., height). This depends on other factors like age and genetic makeup.
However, there are other examples that are not quite as easy to deal with. Sometimes we feel that someone has drawn a questionable analogy, but it takes some effort and careful thinking to say why. Consider the following example:
E.g. 1 "I think people who use the toilet stall designed for people with physical disabilities should be fined. After all, that's what we do to people who use their parking spaces." This sounds ridiculous, and what you want to say is that parking facilities are one thing and toilet facilities are another. But why? What's the real difference between them such that it makes sense to fine non disabled people for using one, but not the other? The answer here might be that it is a much more serious inconvenience to disabled people to use their parking facilities than to use their bathroom facilities. But until you make this point clearly, your claim that there is a false or questionable analogy has not been adequately supported.
Sometimes we might think that someone has drawn a questionable analogy when in fact it is a perfectly good analogy. Suppose you heard the following argument
E.g. 2 "The right way for people to get things from others is to pay for them. So, if what we want is from the people of Brazil is for them not to destroy their rain forests, we should pay them not to do it." This sounds a little bit peculiar, but does it rest on a false analogy? Are these different kinds of wants, such that it makes sense to pay for one and not the other? You might say that they are because ordinarily when you pay for something you get ownership of it, but in fact that's not actually true. What about renting? Or you might say that it just doesn't make any sense to pay people not to destroy their own property. But that's only true given that you have no personal interest in it being maintained. This analogy is, in fact, not an obviously bad one at all. Many economists take it very seriously.
Questionable analogies are very common, but it is also common to accuse people of drawing a questionable analogy when they are actually pointing out an interesting similarity between two otherwise very different things. So whenever you charge someone with drawing a questionable analogy, be sure that the problem is not just a failure of intellect or imagination on your part.