An argument that sometimes fools human reasoning, but is not logically valid. It is crucial to remember that reasoning from definitions and facts to conclusions is fundamentally different from reasoning about definitions. Before you can scientifically establish whether or not Foo is a Bar, you have to establish the meaning of the label Bar.

A given term is associated with one or more definitions and one or more concepts. A definition is correct when it accurately represents a chosen concept. Definitions can be more or less formal, the more formal the better. Concepts are not correct or incorrect, but merely useful.

'''NOTE: The list of logical fallacies should be restricted to those in actual Wiki usage.'''

'''[Please take discussion to FallaciousArgumentsDiscussion. Please. Pretty please?]'''
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'''Formal Fallacies''' (incorrectly constructed logical syllogisms [well, they're not ''all' three part logical errors])
* AntecedentAssumedFallacy (A is true because of B, but B is true because of A) [similar to CircularReasoning]
* ArgumentByAnalogy (A is like B; A has property P; therefore, B has property P) [is this similar to CompositionFallacy?]
* BeggingTheQuestion (A hidden assumption supports the "proof" in process)
* CircularReasoning (A is because of B, which is because of C, which is because of A)
* PostHocErgoPropterHoc (A follows B so B causes A)
* CorrelationImpliesCausation (There is a demonstrated correlation between A and B, therefore A implies B) [same as PostHocErgoPropterHoc]
* NonSequitur (Conclusion does not follow from the premises)
* UndistributedMiddle (All A are C, All B are C, therefore all A are B)

'''Informal Fallacies (well-known)''' [These are fallacies you are likely to find in textbooks]
* AdHominem (The person saying P is biased or otherwise flawed, so P is false)
* AdVerecundiam (P is true because person/entity X has said so)
* ArgumentFromAuthority (quote someone famous) [equivalent to AdVerecundiam]
* ArgumentumAdBaculum (Argument from fear; "If you believe P, you'll suffer for it")
* ArgumentByTheMasses (aka ArgumentumAdPopulum; A is true because "everybody knows it is true")
* EquivocationFallacy (using a term with multiple definitions as if the definitions were equivalent when they are not)
* NoTrueScotsman (Assert that A conforms to B - redefine the identity of A until it does)
* RedHerring (A is true because of totally irrelevant B)
* StrawMan (a weak argument specifically put forth to be knocked down)
* ArgumentumAdInfinitum (aka ArgumentumAdNauseum; A argues longer/more eloquently than B, so A's proposition must be true)
* ArgumentumAdIgnorantiam (if A can't imagine P to be true, it can't be true)
* DisproofByFallacy (aka AdLogicam; Argument has been made at some point for A through error X, therefore A must be false)
* ComplexQuestion (A question contains an assertion assumed to be true, e.g. "Have you stopped beating your wife yet?")
* FalseDichotomy (aka BifurcationFallacy, ThisOrThatFallacy, FalseDilemma; e.g. "You're either with us or you're with the terrorists."; See also ExcludedMiddle.)
* NaturalisticFallacy (Deriving "ought" from "is")

'''Informal Fallacies (colloquial)''' [Most of these are variants of other fallacies or otherwise suggested by contributors]
* ArgumentFromIntimidation (''see also ImmaturityArgument'') ['''not''' the same as ArgumentumAdBaculum]
* AbsenceOfEvidenceIsNotEvidenceOfAbsence (We have never observed a proton decay, therefore it can never happen)
* AnonymousChoir (there are people out there who agree with me)
* ArgumentByGibberish (utter things that turn on the lower third)
* ArgumentFromIncredulity (I can't believe any alternative is true)
* ArgumentByRepeatedAssertion (use "Saddam" and "Al Qaeda" together in the same sentence often enough and eventually they'll believe it, evidence or not)
* ArgumentByFlame. ("C++ sucks. BjarneStroustrup is an idiot. People who use C++ are all lemmings. I'm not going to bother with any legitimate technical critique of C++ because I'm having too much fun flaming; plus I've a got an audience full of fellow-travelers who are lapping this stuff up and patting my back.")
* ArgumentFromSilence ()
* AssumedAgreementFallacy (So-and-so agrees with me on X, so he probably agrees with me on Y too).
* AssumedScalabilityFallacy. (A works well as a small system; therefore it will work well as a large system. Or vice versa)
* AvoidingTheQuestion (The response to a question does not actually answer it).
* ConceptsOutOfContext (B pertains to A when B makes no sense in the context of this A)
* ConfusingTheoryAndPractice (practice of A > practice of B implies theory of A > theory of B or vice versa)
* DesertIslandFallacy (New technology B should be abandoned in favor of old technology A, because B will fail if you're ever stranded on a desert island)
* DisagreeByDistorting (assume an example would be, You want the government to assume restricted responsibility X, therefore you must be a totalitarian socialist)
* DogmaticFallacy (evidence against some X is excluded by the UniverseOfDiscourse)
* DuelingCredentials (I know more about X than you do, so I win)
* EveryoneHasHisOpinion (the opinion of a layperson is as good as that of an authority)
* EvidenceByBestCaseScenario (best case example may distract from problem domain)
* EvilOrStupid (If you don't agree with me, which one are you?)
* ExcerptionNotAbstraction (dogs are animals with four legs, so what about amputated dogs?)
* FailureToElucidate (Using terms more obscure than the primary point at issue)
* GordianReasoning (A is because of B, which is because of C, which is because of D... which is because of Y, which is because of Z, which is because of A) [an extended version of CircularReasoning]
* GrandConspiracy (asserting that the world is being manipulated by a cabal of some sort)
* IdontSufferFoolsLikeYou (Asserting that the opponent is unworthy of debate)
* IfItAintBrokeDontFixIt (Arguing that older things are better than the newer ones)
* IfItAintScottishItsCrap (The merits of X can be determined by some superficial attribute of X)
* IfItsWorseThanMineItsGarbage (If A<X where X is my solution; then A is unsatisfactory)
* IfYouDontLikeItYouDontUnderstandIt (A lack of agreement implies a lack of expertise)
* InventedHere (This can't be particularly good if you did it)
* ItSeemsToMe (substituting opinion for evidence or reason)
* LevelCategoryError (O is the set of all X. All X are drawn with 2 lines so O is drawn with 2 lines)
* NewTechnologyHasFailed (Because it doesn't live up to the hype)
* NewTechnologyWillSaveUsAll (A DisruptiveTechnology it is, trust us)
* NotInventedHere (Arguing that the newest thing is better than the older ones.)
* OneThingAllThings (If you believe X about Y0, you must also about Y1...Yn | n is large)
* OverSimplification (arguing on a level of detail that ignores important details)
* PackageDeal (You can't have A without B, and B is false, so A is false - even though you actually ''can'' have A without B)
* PosthumousAlly (if X were alive, he'd agree with me)
* ShiftingTheBurdenOfProof (P is false unless you prove it)
* SlipperySlope (A might lead to A^n, which is bad, therefore A is bad)
* StolenConceptFallacy (A presumes P which normally follows O, without proving O first)
* SweepingGeneralization (Similar to ArgumentByTheMasses)
* Shifting The UniverseOfDiscourse (A doesn't count in the discussion of B [while it might]) [similar to NoTrueScotsman]
* TheyLaughedAtEinstein (expert opinion on a subject is not trustworthy)
* ThoseNotLikeMeAreAllAlike (B != A and C != A, so B == C)
* WellDesignedFooCanBeBetterThanBar (Some instance of A > some instance of B, so A > B)
* ArgumentumAdHitlerum (P is comparable to Hitler, and therefore evil)

Not all of the above are arguments, some are actions, approaches or strategies. Does that make this page false? According to CriticalSuccessFactor, it does.

''Critical Success Factor need not apply to a Wiki page for it to be useful. Let's not get carried away here.''

See also CarlSagansBaloneyDetectionKit which has another list of FallaciousArgument''''''s.
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CategoryCommunication