Logical Fallacies

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straw man

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This is the fallacy of refuting a caricatured or extreme version of somebody's argument, rather than the actual argument they've made.

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tu quoque

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This is the fallacy of defending an error in one's reasoning by pointing out that one's opponent has made the same error.

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appeal to nature

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This is the fallacy of assuming that whatever is "natural" or consistent with "nature" (somehow defined) is good, or that whatever conflicts with nature is bad.

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slippery slope

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A slippery slope argument is not always a fallacy. A slippery slope fallacy is an argument that says adopting one policy or taking one action will lead to a series of other policies or actions also being taken, without showing a causal connection between the advocated policy and the consequent policies.

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red herring

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This means exactly what you think it means: introducing irrelevant facts or arguments to distract from the question at hand.

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post hoc ergo propter hoc

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(after this, therefore because of this). This is the fallacy of assuming that A caused B simply because A happened prior to B.

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petitio principii

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(begging the question). This is the fallacy of assuming, when trying to prove something, what it is that you are trying prove.

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non sequitur

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"It does not follow"). This is the simple fallacy of stating, as a conclusion, something that does not strictly follow from the premises.

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naturalistic fallacy

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This is the fallacy of trying to derive conclusions about what is right or good (that is, about values) from statements of fact alone.

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dicto simpliciter

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(spoken simply, i.e., sweeping generalization). This is the fallacy of making a sweeping statement and expecting it to be true of every specific case -- in other words, stereotyping.

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complex question

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A complex question is a question that implicitly assumes something to be true by its construction, such as "Have you stopped beating your wife?" A question like this is fallacious only if the thing presumed true (in this case, that you beat your wife) has not been established.

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circulus in demonstrado

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(circular argument). Circular argumentation occurs when someone uses what they are trying to prove as part of the proof of that thing.

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argumentum ad verecundiam

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(argument or appeal to authority). This fallacy occurs when someone tries to demonstrate the truth of a proposition by citing some person who agrees, even though that person may have no expertise in the given area.

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argumentum ad populum

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(argument or appeal to the public). This is the fallacy of trying to prove something by showing that the public agrees with you.

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argumentum ad numerum

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(argument or appeal to numbers). This fallacy is the attempt to prove something by showing how many people think that it's true.

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Argumentum ad nauseam

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(argument to the point of disgust; i.e., by repitition). This is the fallacy of trying to prove something by saying it again and again.

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rgumentum ad misericordiam

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(argument or appeal to pity).

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Argumentum ad logicam

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(argument to logic). This is the fallacy of assuming that something is false simply because a proof or argument that someone has offered for it is invalid; this reasoning is fallacious because there may be another proof or argument that successfully supports the proposition.

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Argumentum ad ignorantiam

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(argument to ignorance). This is the fallacy of assuming something is true simply because it hasn't been proven false.

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Argumentum ad hominem

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(argument directed at the person). This is the error of attacking the character or motives of a person who has stated an idea, rather than the idea itself.

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Argumentum ad antiquitatem

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(the argument to antiquity or tradition). This is the familiar argument that some policy, behavior, or practice is right or acceptable because "it's always been done that way."

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Cum hoc ergo propter hoc

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(with this, therefore because of this). This is the familiar fallacy of mistaking correlation for causation -- i.e., thinking that because two things occur simultaneously, one must be a cause of the other.

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Naturalistic fallacy.

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This is the fallacy of trying to derive conclusions about what is right or good (that is, about values) from statements of fact alone.

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This is an extremely popular fallacy in debate rounds; for example, "Every great civilization in history has provided state subsidies for art and culture!"

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Argumentum ad antiquitatem (the argument to antiquity or tradition)But that fact does not justify continuing the policy.

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"We all know Nixon was a liar and a cheat, so why should we believe anything he says?"

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Argumentum ad hominem (argument directed at the person)Argumentum ad hominem also occurs when someone's arguments are discounted merely because they stand to benefit from the policy they advocate -- such as Bill Gates arguing against antitrust, rich people arguing for lower taxes, white people arguing against affirmative action, minorities arguing for affirmative action, etc. In all of these cases, the relevant question is not who makes the argument, but whether the argument is valid.

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For example, someone might argue that global warming is certainly occurring because nobody has demonstrated conclusively that it is not. But failing to prove the global warming theory false is not the same as proving it true.

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Argumentum ad ignorantiam (argument to ignorance)

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it is common practice in debate for judges to give no weight to a point supported by an argument that has been proven invalid by the other team, even if there might be a valid argument the team failed to make that would have supported the same point; this is because the implicit burden of proof rests with the team that brought up the argument.

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Argumentum ad logicam (argument to logic)

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"Think of all the poor, starving Ethiopian children! How could we be so cruel as not to help them?"

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Argumentum ad misericordiam (argument or appeal to pity).The problem with such an argument is that no amount of special pleading can make the impossible possible, the false true, the expensive costless, etc.

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Tell 'em what you're gonna tell 'em, then tell 'em, and then tell 'em what you told 'em."

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Argumentum ad nauseam (argument to the point of disgust; i.e., by repitition)The appropriate time to mention argumentum ad nauseam in a debate round is when the other team has made some assertion, failed to justify it, and then stated it again and again.

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"At least 70% of all Americans support restrictions on access to abortions."

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Argumentum ad populum (argument or appeal to the public).Argumentum ad numerum (argument or appeal to numbers).Well, maybe 70% of Americans are wrong!

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For instance, some people like to quote Einstein's opinions about politics (he tended to have fairly left-wing views), as though Einstein were a political philosopher rather than a physicist.

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Argumentum ad verecundiam (argument or appeal to authority)debaters should be called down for committing argumentum ad verecundiam only when (a) they rely on an unqualified source for information about facts without other (qualified) sources of verification, or (b) they imply that some policy must be right simply because so-and-so thought so.

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"Marijuana is illegal in every state in the nation. And we all know that you shouldn't violate the law. Since smoking pot is illegal, you shouldn't smoke pot. And since you shouldn't smoke pot, it is the duty of the government to stop people from smoking it, which is why marijuana is illegal!"

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Circulus in demonstrando (circular argument).The best strategy for pointing out a circular argument is to make sure you can state clearly the proposition being proven, and then pinpoint where that proposition appears in the proof.

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"Inasmuch as the majority of black Americans live in poverty, do you really think that self-help within the black community is sufficient to address their problems?"

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Complex question.A question like this is fallacious only if the thing presumed true (in this case, that you beat your wife) has not been established.

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"President Clinton has great economic policies; just look at how well the economy is doing while he's in office!"

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Cum hoc ergo propter hoc (with this, therefore because of this)n debate rounds, what this means is that it is acceptable to demonstrate a correlation between two phenomenon and to say one caused the other if you can also come up with convincing reasons why the correlation is no accident.

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Women are on average not as strong as men and less able to carry a gun. Therefore women can't pull their weight in a military unit."

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Dicto simpliciter (spoken simply, i.e., sweeping generalization).The problem is that the sweeping statement may be true (on average, women are indeed weaker than men), but it is not necessarily true for every member of the group in question (there are some women who are much stronger than the average).

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"Sodomy is unnatural; anal sex is not the evolutionary function of a penis or an anus. Therefore sodomy is wrong."

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Nature, appeal to. But aside from the difficulty of defining what "natural" even means, there is no particular reason to suppose that unnatural and wrong are the same thing. After all, wearing clothes, tilling the soil, and using fire might be considered unnatural since no other animals do so, but humans do these things all the time and to great benefit.

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"This medicine will prevent you from dying" immediately leads to the conclusion, "You should take this medicine."

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Naturalistic fallacy

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"Racism is wrong. Therefore, we need affirmative action."

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Non Sequitur ("It does not follow")

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They say pornography should be legal because it is a form of free expression. But this begs the question of what free expression means."

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Petitio principii (begging the question).This is a misuse of terminology. Something may inspire or motivate us to ask a particular question without begging the question.

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"Most rapists read pornography when they were teenagers; obviously, pornography causes violence toward women."

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Post hoc ergo propter hoc (after this, therefore because of this).The conclusion is invalid, because there can be a correlation between two phenomena without one causing the other.

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"The opposition claims that welfare dependency leads to higher crime rates -- but how are poor people supposed to keep a roof over their heads without our help?"

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Red herring.t is perfectly valid to ask this question as part of the broader debate, but to pose it as a response to the argument about welfare leading to crime is fallacious.

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"If we legalize marijuana, the next thing you know we'll legalize heroin, LSD, and crack cocaine."

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Slippery slope.Tobacco and alcohol are currently legal, and yet other drugs have somehow remained illegal.

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"Mr. Jones thinks that capitalism is good because everybody earns whatever wealth they have, but this is clearly false because many people just inherit their fortunes,"

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Straw man.when in fact Mr. Jones had not made the "earnings" argument and had instead argued, say, that capitalism gives most people an incentive to work and save. The fact that some arguments made for a policy are wrong does not imply that the policy itself is wrong.

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"They accuse us of making unjustified assertions. But they asserted a lot of things, too!"

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Tu quoque ("you too")u quoque arguments play an important role in debate because they may help establish who has done a better job of debating (setting aside the issue of whether the proposition is true or not)