Logical Fallacies LSnK Central
Created: 09-Jun-2006
Updated: 22-Dec-2011

Logical Fallacies

A logical fallacy is a reasoning error in an argument that makes it meaningless or useless. You should never be convinced by a fallacious argument.

Below I explain and exemplify some common logical fallacies. Knowing them will help you to avoid mistakes in your reasoning and better your logical faculties. Note that even the most intelligent of people are prone to these mistakes, since they're often caused by cognitive biases inherent to all humans. What's more, while fallacies are often used mistakenly they are also used to deceive and persuade those ignorant of them.

It's wise to know them well.



Index:
Ad Hominem
Appeal to Emotion
Appeal to Faith
Appeal to Ignorance
Appeal to Tradition
Argument from Omniscience
Association Fallacy
Bandwagon Fallacy
Begging the Question
Biased Sample
Composition Fallacy
Cum Hoc Ergo Propter Hoc
Equivocation
Fallacy Fallacy
False Analogy
False Dilemma
Gambler's Fallacy
Half Truths
Infinite Regress
Jingoism
Just World Fallacy
Loaded Question Misrepresenting the Facts
Non Sequitur
Naturalistic Fallacy
Observational Selection
Poisoning the Well
Post Hoc Ergo Propter Hoc
Red Herring
Reification
Regressive Fallacy
Shifting the Burden of Proof
Slippery Slope
Special Pleading
Statistics of Small Numbers
Straw Man
Tu Quoque
Two Wrongs Make a Right
Unfalsifiability

FAQ



Ad Hominem
Latin for against the man. Deriding someone as if it were a legitimate argument against their position in its own right. The human tendency to agree with people who are on our side makes this a powerful persuader. Don't be distracted by such stupidity. It doesn't matter whether your opponent is an idiot, amoral or insane; it's the argument which must be criticised not the person making it.


Appeal to Emotion
Using emotional manipulation to persuade when it's not relevant. An extremely prevalent practice in advertisements and politics. Appeals to emotion are often used in conjunction with other fallacies to enhance their persuasiveness. Note that this doesn't mean emotion is never relevant - how we feel often matters a great deal.


Appeal to Faith
"You have to have faith to understand. Non-believers can't see the truth..." Arguments that rely on faith ask you to abandon logic altogether and just accept the conclusion as true. It should be obvious that an argument relying on faith alone is useless. Reason is all we have as a means of understanding the world; faith is by definition a belief without evidence, something fundamentally irrational.


Appeal to Ignorance
Attempting to use an absence of evidence as evidence when an investigation has not been undertaken. For example, someone claiming that because we don't know that aliens haven't visited Earth, it's evidence that they have. However, if something has been extensively researched, it is perfectly reasonable to dismiss it if no evidence has been found to support it.


Appeal to Tradition
Arguing that something is good purely because it's tradition. This is of course irrelevant. It can seem persuasive because of the common sense notion that the best ideas tend to survive for longer. But it's a tendency not a fact; terrible ideas persist as well. Slavery has been defended with this fallacious reasoning, for example.


Argument from Omniscience
Arguing that your position is common knowledge, that everybody knows and supports it. For example: "All people believe in something. Everybody knows that." Even if they did, it wouldn't make it true.


Association Fallacy
Arguing that an idea is wrong because some evil person has supported it. For example: "Adolf Hitler was a vegetarian, so vegetarianism must be a sign of evil." Hitler's evil actions had nothing to do with vegetarianism, so the argument is absurd. The converse of this argument is also fallacious. For example, "They called the Wright brothers crazy too; we're revolutionaries just like they were. This perpetual motion machine is sure to work!"


Bandwagon Fallacy
Arguing that something must be true because a large number of people believe it. Of course this has nothing to do with the reality of the situation. An argument must stand on its own merits, not the number of its advocates.


Begging the Question
Using the conclusion of an argument in its premise. Circular logic. This is often done by stating something, rephrasing it and then stating it again as 'evidence'. For example: "The Bible is correct about God existing; it says so and it was written by God." Such arguments are effectively little more than an unreasoned statement, but careful wording can hide the fact and make it seem convincing.


Biased Sample
Generalising from a sample of information not representative of the whole. For example, if you were to do a survey on the opinion of the American people on gun control, asking only NRA members and making a conclusion based on that. This is why samples are supposed to be random.


Composition Fallacy
Arguing that something is true of a larger whole because it's true of a smaller piece of it. For example, arguing that hurricanes are harmless because air molecules are harmless. The opposite of this fallacy is the fallacy of division; arguing that something is true of a small piece because it's true of the whole. An example of this would be arguing that someone must be rich because they live in a rich neighbourhood, or that cells have consciousness because humans have consciousness.


Cum Hoc Ergo Propter Hoc
Latin for with this, therefore, because of this. This fallacy is committed when someone argues that events are causally related purely because they correlate. For example: "This guy went out and killed three people after playing Grand Theft Auto. Violent video games cause violence." No doubt many people also went to the toilet after playing the game, but that doesn't mean the game caused them to urinate. To back such a claim up requires additional evidence that would support a causal relationship.


Equivocation
Using a term with multiple meanings and changing the meaning at some point in the argument. For example: "There's no such thing as a dark feather, all feathers are light." The property in question changes from shade to weight, making the argument nonsensical. This fallacy can be employed much more subtly and to greater effect. An example: "Faith in God isn't irrational; you have faith in your fellow man, don't you? Isn't that rational? So isn't faith rational?" The second instance of the word 'faith' means a sense of confidence in the ability or nature of others, not a religious belief.


Fallacy Fallacy
Arguing that someone's position is incorrect purely because they've used fallacious arguments in their attempts to support it. Of course, the conclusion may still be true without being established by the associated argument. Note that it's not a fallacy to be unconvinced by a poor argument; this fallacy is comitted when one rejects the possibility of its conclusion outright because it's been badly argued for.


False Analogy
A false analogy is an analogical argument in which the entities used are too dissimilar to make a meaningful inference from. Even good analogical arguments are never rock solid. For an example of a bad one, consider Paley's watchmaker argument: he argued that the Universe is like a watch, and like a watch, it's logical to assume that the Universe was designed by something. The problem is, we only know watches are designed because we designed them and have a basis for comparison in other objects. The same reasoning is inapplicable to the Universe.


False Dilemma
Also called bifurcation or a false dichotomy. Arguing that only two [or more] choices can be taken when more options are available. Consider George Bush's infamous quote: "You're either with us or you're with the terrorists." Obviously there's another viable stance to be taken: neutrality. Even that's an oversimplification: like many topics, allegiance is better represented as a continuum not two or three discrete positions. Intellectual laziness and the appeal of simplicity make this tiresomely commonplace.


Gambler's Fallacy
Assuming past events affect future ones in random sequences. For example, somebody watching a horse race might notice that one of the horses is constantly losing and instead of avoiding betting on that horse, they bet on it because it's "Due for a win." The fact that a random sequence has recently followed a specific pattern does not mean it will change soon or continue. It's random!


Half Truths
A half truth is when someone omits information when describing a subject, thereby disguising its true nature. It's highly effective because the partial inclusion of the truth makes an argument seem more convincing, even if those facts aren't relevant. This is another fallacy that sees frequent use in politics and advertisements. Conspiracy theorists thrive on it.


Infinite Regress
An arguer commits this fallacy when their argument has an explanation which itself requires an explanation, which needs another explanation, and so on; the explanation is never adequately supported. Take this for example: "All things must have a cause. The Universe must therefore have a cause. The cause must be God." But if all things must have a cause, then God must have a cause, and its cause must have a cause, and so on forever. Nothing is explained, the argument is useless.


Jingoism
Irrationally appealing to patriotism, a form of emotional manipulation. Take the American 'Patriot Act' legislation; its title has connotations of freedom and justice in America, but the content of the act serves to make it easier for the authorities to spy on citizens without due knowledge or consent, hardly an activity the population considers patriotic. In fact, it directly opposes a principle directly stated of the country's constitution.


Just World Fallacy
Reasoning based on the assumption that the world is fundamentally fair and just. You've undoubtedly heard this line of thought before: that the poor must be lazy and deserving of their poverty while the rich have all worked hard for their fortunes; that victims of rape were asking for it but rapists weren't in control of their actions. Everyone deserves what they get. We all want to think that evil is punished and virtue is rewarded, and some people operate under the delusion that it really is.


Loaded Question
Assumptions formed into questions, which when answered imply that the assumption is correct regardless of a negative or positive response. A classic example is, "Have you stopped beating your wife yet?" Whether you answer yes or no, you answer that you have a wife and that you beat her.


Misrepresenting the Facts
Simply using false information as the premise of an argument. While it makes the argument irrelevant to the matter at hand, it can still be convincing if it seems reasonable. Most people don't corroborate what they're told, especially if they agree with it. Verify facts for yourself; if you can't then don't make up your mind. Another favourite among conspiracy theorists.


Non Sequitur
Meaning it does not follow, these are arguments with conclusions or inferences that don't necessarily follow from the premises. The fallacies presented here are all specific types of non sequitur.


Naturalistic Fallacy
Also called 'appeal to nature'. Arguing that something is good purely on the basis that it's natural; essentially that anything natural is good and anything unnatural is bad. Of course naturalness has nothing to do with goodness. Medicine isn't bad because it isn't natural; conversely, death isn't good because it is. This trick is employed often in advertisements for food and so-called alternative medicines.


Observational Selection
Highlighting only positives when there are also significant negatives or vice versa. Casinos attempt to induce this by design; loud sounds signify winners but losers are left in silence. It appears as if many people are winning and that the odds are favourable, but the losers greatly outnumber the winners. Not really a fallacy, but worth being aware of.


Poisoning the Well
Attempting to stop people from considering an opponent's argument by using ad hominems, lying about them, or otherwise attempting to instil bias where there should be none. This is unfortunately par for the course in political arguments and even mainstream politics. In America there are entire campaigns based on it; arguably entire news networks. The bottom line: always try to check your facts and always try to consider arguments on their own merits.


Post Hoc Ergo Propter Hoc
Latin for after this, therefore because of this. A common fallacy in which someone assumes that because a certain event occurs before another, the first event is the cause of the second. However, one thing occurring after the other isn't necessarily sufficient reason to assert a causal relationship. Imagine the following for example: a primitive tribe beat their drums during an eclipse, and when the Sun inevitably becomes visible again they conclude that they caused it to return, unaware of the fact that it was a natural astronomical phenomenon and that their actions had no influence. This is why controls are used in scientific experiments - they rule out non-contributing factors, narrowing the potential for error.


Red Herring
When someone attempts to change the subject in order to divert attention from an argument, it's a red herring. This is often achieved by introducing an unrelated but emotionally charged topic. Or as we call it on the Internet, 'trolling'.


Reification
Inappropriately treating abstract concepts such as relationships or arbitrary groups as if they have the properties of definite, 'solid' entities. Fine for illustrative purposes in writing but not for reasoning. For example, an advertisement announcing that you should "Use Natural-Herb X, because nature always knows best." Nature doesn't know anything; it's a concept.


Regressive Fallacy
Failing to consider natural fluctuations in things when determining their causes. This is a common fallacy that leads to many erroneous beliefs. For example, quack 'medication' like magnetic healing rings. Someone may use them and feel better and conclude that they work. But that isn't necessarily the case. The severity of illnesses and their accompanying pains tend to fluctuate over time. The most likely time someone will take some medicine is when their pain is at its worst. The pain will fluctuate and become less severe, leading them to believe that the medicine had some effect, whether it did or not.


Shifting the Burden of Proof
Changing who has to provide the proof in an argument. For example, "UFOs have abducted people. Prove it's not true!" The burden of proof rests with the positive claimant; in this example the person arguing that UFOs have abducted people. It doesn't matter if there's nothing to suggest it isn't true when there isn't anything to support it either.


Slippery Slope
Arguing that one action will inevitably lead to another, which will lead to more unfavourable ones and that the latter are good reason to disallow the first, when in fact there's no definite evidence that the initial action will actually lead to the later ones. For example: "If we legalise marijuana, then we'll end up legalising LSD, then crack, and the whole country will end up addicts." Legalising marijuana doesn't necessarily lead to legalising cocaine. Widespread availability does not necessarily lead to widespread use. Widespread use does not necessarily lead to widespread addiction.


Special Pleading
This fallacy is committed when someone supports their argument by asserting that their argument requires special consideration, when the consideration is not verifiable or relevant. Someone may argue that "You're male, you can't understand the arguments supporting abortion." The implied reason is that males can't empathise with females because they can't get pregnant. But the systems in your brain that facilitate empathy and comprension don't depend upon the configuration of your genitals.


Statistics of Small Numbers
Or hasty generalisation. Generalising tiny samples of data as being representative of the overall statistic, typically personal experience. Example: "I went to a gay nightclub once, they were all going at it. Gays are obsessed with sex." You may as well roll a dice once and conclude that all the sides have the same number. Personal experience doesn't give you a realistic understanding of macroscopic phenomena.


Straw Man
Misrepresenting an opponent's argument and refuting that misrepresentation instead of what they actually said. For example: "The Theory of Evolution says that complexity in the Universe increases over time. The Second Law of Thermodynamics says that any increase in complexity is impossible. Hence, the Theory of Evolution is inconsistent with the laws of thermodynamics." To the ignorant this may seem convincing. However, evolution only applies to biological organisms and the second law only applies to closed systems and doesn't forbid localised increases in complexity. The Earth is not a closed system, unless you discount the existence of a certain scathing-hot radioactive plasma ball tirelessly pouring energy onto our planet.


Tu Quoque
Latin for you too. Arguing that because someone has done something contrary to their argument, it must be wrong. In other words, that when someone is hypocritical their argument is wrong. While it may be unpleasant to be told killing is wrong by a murderer, the fact that they have done so does not mean they are incorrect. This holds for any position no matter how annoying.


Two Wrongs Make a Right
Reasoning under the assumption that when someone does wrong, another wrong balances it out. For example, when being repremanded, it's relatively common to hear schoolchildren argue that their actions are justified by other children engaging in the same activity. Many of us have heard cries of "She lied too!" or perhaps even said it. Another example is supposing that it's okay to do something wrong to someone because you think they would've done it to you. In all of these cases, what is occuring is the erroneous justification of wrongdoing based solely on the fact that others have done the same - the fact that someone else does something wrong does not make it right.


Unfalsifiability Fallacy
Making an argument based on premises that can't be tested. For example, imagine someone arguing that you should believe in their god because if you don't, you'll suffer for eternity after you die. But does the god even exist? Does that kind of afterlife even exist? If they did would you really suffer for not believing? The catch is, you can only find out by dying. Better change your lifestyle, you never know!




FAQ

I get asked some interesting questions about this page. Probably the most useful type to discuss here are ones which contain the following notion: that one of my examples, despite having incorrect reasoning, must actually be correct purely because the conclusion is correct.

Simply put, reasoning doesn't work that way. The conclusion is the result of the preceding reasoning process, without which it is simply an assertion. Whether you should accept the argument and its conclusion or not depends on the reasoning.




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