Topic: Logical Fallacies do not an Argument Make (READ)

[Vekseid]

So this has been a problem here, and so far my major refutations of this sort have generally been in private messages with people, mainly in warnings to two members who will not be named, and even then the scope was rather limited. Certain fallacies - such as personal attacks and appeal to ridicule - have ended up with harsher measures against those who perpetrate them (and still will). I have been wanting to do this for a long time - three and a half years, even, but I always came up with one bs excuse or another to put it off.

That ends with this thread.

First.

You do not need to memorize this list. Even if we say that reading this list is mandatory as response to a warning, memorization isn't a requirement - properly presenting your argument is. Hell, you don't even need to read this list. You can find another fairly comprehensive list here on a single page if you don't particularly trust us.

It is and always will be incomplete, for one, and for two, no one is perfect. We are not expecting you to make your point flawlessly. Nor is the goal here to get people to run over every post looking for the slightest flaw and then to sound klaxons with it. Regardless, anyone can learn from studying logic, and people who constantly engage in fallacious 'debate' behavior are going to be given their warning, or castrated if they recently received one, just like everyone else.

Fallacies are not about factual errors. Errors in fact should be resolved by finding the proper fact. Fallacies do not always apply. They are about debates, a certain amount of common sense needs to be applied. Again, no one is perfect, least of all myself. People are going to make mistakes - think of this thread as a knife sharpener, not the knife itself.

Vekseid: I loved Final Fantasy 7. I cried when Aeris died.
Trieste: Appeal to emotion!
Vekseid: Fuck you. : (

Sometimes an argument uses as its basis what would on its own be determined as a fallacy. For example, opposing gay marriage is by definition an appeal to tradition or special pleading, depending on one's choice of argument. This does not automatically make the argument invalid, because in order to be fallacies, they must lack logical reasons for such positions - proving that the tradition is in fact better or that the gender of a couple is a relevant difference. Fallacies used in support of or opposition to banning gay marriage are not magically made logical, however.

The reason I am providing our own list here, instead of just linking to another list, is because I want something people can read and grasp in one sitting, and explain things in my own words. It is important to note that a phrase can be the victim of more than one fallacy at a time. This can make classification difficult above and beyond the subtle differences between what follows.

All that said, this should help people get to the core of debates a great deal faster. It is a lot easier to formulate your own argument if you know what flaws you yourself may end up succumbing to, and thus the core point can be the issue rather than dancing around it.

If you have a correction or addition to this list, please PM me. I have probably made quite a few such errors. : /


First, let's get a special case out of the way:

Loaded Question 'Complex Question' - the most famous of these is "Have you stopped beating your wife yet?" - when asked of someone who may not even have a wife, much less beat her, much less have known evidence of it. Similarly, a complex question can involve asking two questions in the same phrase. "Do you support the right of gays and felons to vote?" You can support one without supporting the other. Note that, technically, a loaded question is not necessarily a fallacy - they are usually questions and questions are usually not arguments.

Just because it is not usually a fallacy does not mean you don't deserve a good smacking for pulling stunts like this.

[Vekseid]

Formal Fallacies

A formal fallacy can be expressed as faulty reasoning - the premises may be correct, and even the conclusion may be correct, however a formal fallacy means that the conclusion does not follow from the premises in the manner described by the argument.

For example, a typical undistributed middle fallacy may be presented as "All men are human, all catholic priests are human, therefore all catholic priests are men." The premises are true, the conclusion is true, but the reasoning is faulty.

For now, I am going to avoid fallacies of categorical syllogisms like the above. I want a post people will read, and they are rather more boring than a lot of others. This does not mean you cannot benefit from structuring your argument in that fashion, nor from studying them. Fallacyfiles has a list of syllogistic fallacies here.


At Least Read These

These two fallacies are probably the most important - just because an argument is not correct, it does not follow that the conclusion is therefore false.

This is not carte blanche to resort to fallacious arguments. Being called out on a fallacy entails a need to rectify the problem, not spew garbage.

Bad Reasons Fallacy - claiming that because the method is incorrect, the conclusion must therefore be false.
A: "C stripped for me on webcam, I know she's a girl."
B: "Dude, C could be a post-op transexual! You can't be absolutely certain, so C is a guy!"
Just because an argument is not completely sound does not make it false. You can come up with any number of unsound reasons for two plus two to equal four, but that does not change the fact that two plus two does indeed equal four.

Fallacy Fallacy 'Argumentum ad Logicam', 'Fallacist's Fallacy' - claiming that because an argument is founded on a fallacy, it is therefore false. "That's an appeal to authority! Sorry, but that means cats are not mammals!" etc. etc. This is a more specific - and more typical - version of the bad reasons fallacy above.


Modal Fallacies

Modal logic could be thought of as classifying the 'quality' of a statement - something can be possibly true or false, or certainly true or false. For example, two plus two is four, and this is always true. You happen to be awake while reading this, but - assuming you are human - you occasionally do sleep. In English and other natural languages, the words that signify certainty instead of possibility can be one and the same, sometimes depending on context.

Billy wants to enter the roller coaster ride. He must be at least 48 inches tall.
Billy rode on the roller coaster ride. He must be at least 48 inches tall.

The meaning of the second sentence is changed by the previous sentence - in the first example, it is a requirement. In the second, it is a conclusion from the previous requirement. Letting these sorts of ambiguities persist in an argument can lead to fallacious statements:

"If my mother and father have three daughters, I have to have at least one sister."
"My mother and father have three daughters."
"Therefore I have to have at least one sister."

Typically, we automatically work out the resulting ambiguity in the third sentence. That I have at least one sister, rather than I, for some mystical reason, must have at least one sister as if having a sister is some sort of predicate for my existence. The extraneous 'have to' in the conclusion is discarded and we move on. Not being sufficiently clear, however, can lead to assumptions getting made that have no business being made.

For example, it is widely known that abiogenesis, as we currently understand it, cannot occur in an oxygenated atmosphere. Since Earth's atmosphere is currently oxygenated, and abiogenesis cannot occur in such an atmosphere, some then infer that life could not have naturally began on Earth. Of course, we also know that Earth's oxygenated atmosphere was the result of a billion-year process that began after life came to be, and thus our atmosphere was not always like this. Just because Earth's atmosphere is currently oxygenated, does not mean that it always was.

I sincerely hope that was clear. : /

A warning: It is easy to 'miss the point' when applying this fallacy. A lot of these examples are either a factual error (see previous example) or a lack of clarity (logical fatalism - define free will for me, please).

Another example of the modal fallacy that may be illustrative: "Assume time travel is possible, and that we only have a singular reality such that any changes a traveler makes will recursively apply to them. Assume that a traveler does go back in time, and kills their grandfather..." this rather typical paradox is considered a modal fallacy by some philosophers, namely Norman Swartz who came up with something a bit like the Novikov self-consistency principle, though not as rigorous. The final phrase - killing your grandfather after the previous conditions are satisfied, is described as being possible when in fact it is not. Thus, if that sort of time travel is possible, and you go back in time before your father's conception, you do not kill your grandfather - amongst other things that you do not do.

Modal Scope Fallacy 'The Modal Fallacy' - largely as described above, though the most obvious one is the difference between me having a sister and having to have one. The link covers one of the typical examples - "That we can't really know anything." 


Propositional Fallacies

These fallacies crop up in evaluating the truth of individual parts of an argument itself. If it's snowing and January, then you know that it's snowing, and that it is January.

Commutation of Conditionals 'Converting a Conditional' - "if a then b, b then a" "If all Vestal virgins are women, all women are Vestal virgins." When switching such things around actually does apply, it's called 'if and only if'.

Affirming a Disjunct 'Alternative Syllogism', 'Asserting an Alternative', 'Improper Disjunctive Syllogism' - when taking an 'or' clause to be exclusive. "You are a buddhist, therefore, you are not a taoist." Far eastern philosophical traditions are not mutually exclusive the way modern interpretations of near-eastern religions are.

Denying a Conjunct 'Disjunctive Syllogism' - "Not a and b. Not a, so b" - "It can't be both Monday and Wednesday. It's not Wednesday, so it's Monday." Ignoring that all given options can be false.

Affirming the Consequent or asserting the consequent is described as 'if a, then b. b, so a'. "Getting hit in the face causes bloody noses. You have a bloody nose. Therefore you were hit in the face." Note that this should not be confused with something being an indicator - a bloody nose is generally not healthy and running through a list of possibilities is not unwarranted.

Improper Transposition 'Negating Antecedent and Consequent' - declaring 'if a, then b. not a, so not b' - simply negating a logical equation is not a valid form. "If we eat arsenic, we will be poisoned. If we don't eat arsenic, we won't get poisoned."

Denying the Antecedent 'Fallacious Modus Tollens' - like an improper transposition, but refers to other causes being overlooked. "Getting hit causes bruising. You haven't been hit, therefore you don't have any bruises." - not all effects have a single cause.


Quantificational Logic

Quantifiers are many and varied, but these fallacies deal with mistakes that get made using the words 'some' and 'all'.

Existential Fallacy 'Fallacy of Existential Assumption' - The assumption that all X are Y, therefore some Y are X. "All winged dragons are animals, therefore some animals are winged dragons." The former is true, but the latter does not necessarily follow.

Illicit Conversion 'False Conversion' - "All Trinitarians are Christian, therefore all Christians are Trinitarian." Just because a fallacy is seventeen centuries old does not make it valid.

Illicit Quantifier Shift swapping the quantifiers along with the terms. "Every child has a parent, therefore there is a single person who is the parent of every child." This can seem like a tempting conversion - the conclusion is true when talking about human ancestry, for example (Y-Adam and Mitochondrial Eve), but this fallacy is not the proper means to reach that conclusion.

Some are / Some are Not 'Unwarranted Contrast' - "Some mammals are animals, therefore some mammals are not animals." 'Some' is a subset of 'all'. A person not familiar with a subject may have an incomplete understanding of it, especially if it's a new subject, so may hold back from stating 'all'.


Lying with Statistics

It seems that most logicians place these sorts of fallacies into the 'informal fallacy' category, however, engaging in these fallacies requires, as far as I can tell, that formal logic be violated. You can translate the proof against the Gambler's Fallacy into a set of syllogisms, for example:

Flipping a fair coin nine times in a row and receiving heads each time has a probability of 1 in 512.
Flipping a fair coin ten times in a row and receiving heads each time has a probability of 1 in 1024.
Therefore the difference in probability between the ninth and tenth flip coming up 'heads' as well is exactly one half.

The difference in probability between the ninth and tenth flip coming up 'heads' as well is exactly one half.
The probability of flipping a fair coin and the result coming up heads is one half.
Therefore the probability of heads turning up after nine coin flips does not change if the previous nine flips were heads.

This is, of course, an inductive versus deductive example. That is, I am not proving it for all cases, but I am not blindly agreeing with my source, here.

Gambler's Fallacy 'Lady Luck has no memory' - truly random events cannot be predicted from previous outcomes. The Gambler's fallacy is the belief that a string of random results will eventually return to the mean - that if you get fifty results on a die from one to five, that somehow increases the chance of you getting a six on your fifty-first roll. If you roll a die fifty times and it never once shows up as a six, the fifty-first time still only has a one in six chance of turning up a six, even though the odds of a one to five result being obtained fifty-one times in a row is about one in eleven thousand versus about one in nine thousand for fifty times in a row.

Hot Hand Fallacy 'Lady Luck really has no memory' - this is the opposite of the Gambler's Fallacy - the belief that a random streak will continue. Just as fifty results for a one to five do not increase the probability of receiving a six on the next roll, they do not decrease that probability, either.

Conjunction Fallacy 'Conjunction Effect' - this fallacy seems to result from the implicit belief that increased detail makes a thing more likely to be true. "Which is more likely, that I am a single male, or a single male of age twenty-eight?" The latter possibility is completely encompassed by the former, and thus will always be less likely.

Base Rate Fallacy 'Neglecting Base Rates' - this fallacy is a math problem in disguise. "Left handed people are three times as likely to be professional baseball players as opposed to right handed people. What percentage of professional baseball players are left handed?" (Note: statistic was pulled out of my hind end, don't trust it) in answering this, one might implicitly assume that the number of left handed people and right handed people are equal, leading some to incorrectly answer "75%". If you instead note that 10% of people are left handed, you come up with three left handed professionals for every nine right handed professionals, or 25%. Note that assuming the ratios of male and female left-handers is identical and their equality in participating in professional baseball is also a base rate problem.


Miscellaneous

Where odd ones out go.

Masked Man Fallacy 'Illicit Substitution of Identicals' Substituting one representation for another is not necessarily valid inside context. Someone might be aware of my handle (Vekseid), my normal Internet handle, and my real name, all of which are recognized by several hundred people, and not realize that they are all 'me'. "Vekseid said hi." Does not mean they used my real name in that conversation.

[Vekseid]

Distractions

'Red Herring, 'Smoke Screen', 'Wild Goose Chase' - this section covers any attempt to divert the argument from one issue to another. "You may not want to mow the lawn, but frankly, I think you need to start wearing deodorant."

Red Herrings are rather common on forums. "Going off topic." Inside a debate, usually a signal that they belong in a new topic, assuming they warrant discussion at all - see below. Distractions are informal fallacies, but since they're so common on forums I felt they deserved their own section.


Genetic Fallacy

Attacking the history of a claim rather than the claim itself is called a genetic fallacy. This is the most generic such fallacy - ad hominems are the most common genetic fallacies. "Fox News reported on an Earthquake last night, but it's Fox News, therefore it probably never happened." Note that this doesn't apply when the discussion is about the quality of the source itself - if someone has lied habitually in the past, using that as a basis for calling them a liar is not a fallacy.

Ad Hominem - 'Against the Person' is where an element of the person is used to discredit the argument itself. It can be true, and it is not necessarily even an attack - though it can be. For example, "Vekseid runs Elliquiy, therefore statements he makes in favor of it are false," is an ad hominem, however true the first phrase may be.

Tu Quoque - 'You too' is a form of ad hominem where someone's previous or even current behavior is inconsistent with their current argument, and this is taken to be evidence against their current position.

Example: Mitt Romney once opposed abortions except for certain instances, and then came out in support of them. Using this as evidence against abortion commits this fallacy. Using it as evidence that he may be changing his mind for political reasons - a 'flip flopper', does not commit this fallacy, however.

- Compare to Special Pleading - a person is not exempt from criticism because of this. For example, smoking is bad, a smoker may hold this view, but cannot justify a special exemption for themselves beyond the fact that they are currently addicted.

Poisoning the Well - a form of ad hominem in which the information (true or false) is instead provided before the argument itself, instead of being a part of the argument. It is called poisoning the well because it is generally used to provoke outright bias. "And now, introducing Ted Stevens, convicted felon..." It can be difficult to avoid in a forum debate - it's important to keep all biases, including developing ones, separate from factual information presented.

Personal Attack - 'Ad Hominem Abusive' - a form of ad hominem in which the ad hominem also has a negative connotation, whether true or false. "Vekseid is a fatso, of course he likes pizza." - note that the particular fallacy here is that it's inferring that all fat people like pizza - I certainly do like most pizzas. "Vekseid is fat, therefore his diet is improper." is not a fallacy unless I shed a few dozen pounds.

Circumstantial Ad Hominem - attacking a claim because it is in the claimer's interest to make that claim. "Of course you favor lower taxes, you're rich!" is such a fallacy. 

Etymological Fallacy 'Abuse of Etymology' - where a claim is made using an older or archaic meaning of a word. "Man originally meant 'person' and the prefix 'hu-' has the same Indo-European root that 'Earth' does, meaning soil, as in person of the soil, or one who grows crops. Therefore hunter-gatherers are not human." This also illustrates how this can be quite a distraction - the etymology of some words can be very interesting, but it does not necessarily lend credence to claims made with them.

Appeal to Ridicule 'Appeal to Mockery' or 'The Horse Laugh' - rather than presenting a factual assertion, an appeal to ridicule simply mocks it. "That's sad/crazy/insane/stupid/absurd." Note that this differs from ad hominem in that while an ad hominem attacks the person making the argument, an appeal to ridicule attacks the argument itself. This should not be confused with reductio ad absurdum - reducing an argument to absurdity (ie, proof by contradiction). "No white people speed." "Absurd, I'm white, and I was speeding yesterday."

Appeal to Misleading Authority 'Fallacious Appeal to Authority', 'Misuse of Authority', 'Irrelevant Authority', 'Questionable Authority', 'Inappropriate Authority', 'Ad Verecundiam' - where a statement or belief by someone without unbiased expertise in the area is used as evidence. "Fred Hoyle, a famous astronomer, said that evolution is impossible because he says the statistics make it so." Fred Hoyle is an astronomer, not a chemist, much less a biochemist, and on top of being an astronomer he's partly famous for being vehemently wrong about the Big Bang. This specific argument is also confusing chemical evolution (abiogenesis) with evolution, when Fred Hoyle made no such mistake, an attribution fallacy or a linguistic fallacy, depending on whether or not it was intentional.  A valid appeal to authority is generally used as a shortcut for a more thorough explanation - "You can't make a post at 4:31 AM CST because Vekseid said so." is valid because I manage the server and that's when the daily backup runs. I've no business translating Chinese for you, however.

Appeal to Celebrity 'Cool person said this' -  "Vekseid supports it so it must be right!" And other such nonsense. A type of Appeal to Misleading Authority, someone's fame has much less bearing on the truth or falsity of their opinions than their supposed expertise.


Guilt by Association

Where a claim is discredited because of some form of opposition to other people who support it is present. "Stalin was an atheist too, you know." So was Alan Turing. The story of why Stalin was an atheist and what lessons he took from that is a great deal more telling.

The Hitler Card 'Godwin's Law' - Hitler was a vegetarian, opposed tobacco, supported eugenics and opposed immigration. "Hitler supported the affordable car (Volkswagon), therefore affordable cars are immoral." That is not to say that any of the positions listed are good or bad, but if so, their quality is separate from whether or not Hitler believed in them. Despots do not rise to power by being continually and absolutely wrong.


Appeal to Consequences

Using the results of a conclusion to discredit the conclusion. "Nuclear bombs cannot generate radiation because that would mean thousands of people would get radiation poisoning, suffer and die if one were detonated near them." is a suitably absurd example. "There must be an afterlife because otherwise how can there be true justice?" is not absurd, however the desire or need for true and final justice is not a valid premise on which an afterlife can be based.

Appeal to Fear 'Scare Tactics', 'Appeal to Force', 'Ad Baculum' - is a type of appeal to emotion using a fearful assertion as evidence. "Nice car. It's a shame if something would happen to it... how about you pay me $50 for insurance to make sure that nothing happens to it?" Note that paying the mafia $50 for their protection racket may be prudent, it is not, however, rational. Threats are not the only form of this fallacy - "If we do x, then the terrorists win!"

Wishful Thinking "It is true because I want it to be." This should be fairly obvious, and some people simply accept this sort of thing on its face - ie a just afterlife. It is not, however, evidence.


Appeal to Emotion

"It just looks better" "I hate it." - an assertion that relies on an emotion as its base, rather than a fact. People trying to sell you something usually do this, which can be rather amusing in spam. "Don't you want bigger breasts?" - No, I'd like to lose the manboobs, thanks.

Appeal to Pity 'Ad Misericordiam' - Using pity or misery as evidence for a position. "You must believe in angels because I have cancer." Note that the generation of pity does not mean that this fallacy has occurred. "I'm sorry I could not call you yesterday, but chemotherapy left me unconscious." The resulting facts of a pity-generating cause are logically valid, and often why we feel pity in the first place.

Appeal to Spite "Because of x, I'm going to y". Using spite as the basis for a decision is a logical fallacy. "GothicFires made another role playing site, therefore I'm banning her from Elliquiy." Note that, as in the appeal to pity, an assertion may generate spite and not fall into this fallacy. "Why do you go back to him if he keeps beating you?" is not a fallacy, even though it may create spite.

Appeal to Flattery 'Kissing Ass'. Anyone who runs a large community is quite familiar with this one. "You are awesome! Can you just give me a bit more time on this test?" Note that this requires the flattery to be used as a reason for a position. "Thank you for giving me more time on my test, you are awesome!" is not necessarily a fallacy.


Populist Appeals

Because everyone else / others have, so should you.

Appeal to Popularity 'Ad Populum' - is related to an appeal to emotion and is sometimes combined with it. "People like Obama more than McCain, therefore he is better capable of leading our country." Like any fallacy, it does not mean the conclusion is wrong, merely the path getting there. Note the difference between this and appeal to belief.

Appeal to Tradition 'Appeal to the Old', 'Old Ways are Best', 'Fallacious Appeal to the Past', 'Appeal to Age' - an appeal wherein an old method is preferred over a newer one simply because it's previously been done the old way. "We always light a bonfire at noon on Sunday, therefore we should do so next Sunday." Note that being a tradition does not invalidate something, it simply is not an assertion that can be used to support a conclusion. See Appeal to Novelty. Likewise, there can be a definite quality about something's age - we ban pedophilia here for a reason.

- There's a special example of appeal to tradition called 'linguistic purity', which is typified by anal English teachers but it's more formalized with languages that have official language bodies ie French. Stopping linguistic drift is generally considered by linguists to be laughable, though a high literacy rate helps. As much as you or I may hate the word 'blog', sorry, it's here to stay.

Appeal to Novelty 'Appeal to the New', 'Newer is Better', 'Novelty' - just because something is new does not make it better. "Let's all start driving in reverse!" As with an appeal to tradition, the newness of a thing does not mean it -isn't- better. A security fix is almost always a good thing, for example. In both cases, they are merely qualitative statements and not reasons in and of themselves.

Appeal to Common Practice "Most people do it this way." Just because that may be true does not necessarily mean that the common way is better. Often used to justify corruption - "Other people are cheating on their taxes, so we should too." Note that common practice can be a valid reason for a certain behavior - the entire Internet is built on establishing protocols and following them.

Appeal to Belief "Most people think it true." The ratio of people who believe in something does not have any independent bearing on whether or not it is true. "Most people believe in God, therefore God exists." Likewise, it can be true, it's just not a valid reason for the conclusion - "Most people believe the Earth is round."

Bandwagon 'Peer Pressure' - because your friends are during it, you should too. I think pretty much everyone is familiar with this one. Just say no, people. Just say no.


Miscellany

Straw Man "Voodoo debating" - where an argument is presented against a mockery of a position rather than the position itself - like attacking a voodoo doll attacks a person. "Eat your vegetables, Johnny. You don't want to starve to death, do you?" A valid argument is trained against the original position.

Two Wrongs Making a Right "But three lefts do." An incorrect action is not necessarily the proper response to another incorrect action. Literally, 'two wrongs don't make a right'. Can also be an appeal to spite - "He hit me the last time I saw him, therefore I'm going to hit him when I see him again." Note that there can be other reasons for taking hostile action - self defense, for example.

[Vekseid]

Informal Fallacies

Informal fallacies are those that are not formal - and include distractions - but they specifically imply that there is something wrong with the actual content of the arguments themselves, rather than formal logic itself.


Ambiguity

We're all rather familiar with this one, innuendo is of course our specialty. I could try to count the various euphemisms for sexual acts mentioned on these boards. In a debate, however, it's important to be clear, though trying too hard can also be trouble.

"Walking into bars tends to result in headaches."

Accent - technically a fallacy but much less of one in English than in other languages - ie Greek from where it originated. English tends to use tonals and stress to enhance meaning rather than change it outright.

Amphiboly "Slippery when wet." - where a phrase has two separate meanings. I can't think of one that does not involve some sort of innuendo right now. Maybe I'll edit this later when my mind is out of the gutter. That may take awhile.

Scope Fallacy an amphiboly that turns on a single word having multiple, separate modifications in context. "He must be strong." Can either be a requirement or a conclusion, for example.

Equivocation 'Doublespeak' - a single word can have multiple meanings, not just in terms of grammar (scope fallacy) but also the word itself. "Do you have an appendix?" is an innocuous example that can be rooted out by context.

Redefinition 'Arbitrary Redefinition' - care needs to be taken when modifying a term's definition. It's sometimes unavoidable, especially when dealing with new concepts. Political ideologies suffer rather heavily from this, and can have some amusing results - compare social liberalism with economic liberalism. Remember that you are discussing things with an international audience.

Vagueness - vagueness as separate from ambiguity can be taken in the sense that ambiguity relies on multiple distinct meanings, and vague terms in a debate usually have a single meaning but borderline cases. "He's huge!" has a different meaning to a five foot tall person and an eight foot tall person.

Out of Context taking someone's words out of their original context in order to distort their meaning. This does not necessarily mean just the phrases that surround the original text - "God does not play dice with the Universe." is taken by some as evidence that Einstein believed in a personal God. However:

I do not believe in a personal God and I have never denied this but have expressed it clearly. If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it.

Creationists in particular are famous for this fallacy. In one example, a quote is taken out of Origin of Species where Darwin marvels at the complexity of the eye. One might quote only the beginning of a paragraph:

Organs of extreme perfection and complication. To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.

And omit what follows:

Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself first originated; but I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound.

Darwin then goes on for the next several pages expounding on this.


Unsupported Claims

Claims that have weak or no actual support. They either rely on themselves in some fashion (Begging the Question) or simply involve an assertion out of nowhere (Slippery Slope, etc).

Begging the Question 'Circular Reasoning', 'Petitio Principii' - a form of argument in which the conclusion is used as support for itself. "Vekseid is God because he says he is." An argument must rely on something besides itself.

Question-Begging Analogy - an analogy which does the begging. Comparing abortion to infanticide, for example, begs the question - at least among pro-choicers - about whether a fetus holds the same status as an infant.

Loaded Words 'Loaded Language' - using language with connotations in order to influence a belief. "Proper Christians oppose abortion." Again, apply common sense - "Proper Christians believe in Christ as their savior." is not a fallacy because one of the primary definitions of Christian is that belief. Loaded language is only a fallacy when used to support the argument, obviously, else you could call Elliquiy one giant collection of fallacies : )

Appeal to Nature 'Argumentum ad Naturam' - claiming that natural things are better. "It's natural to be naked, so we shouldn't wear anything to the arctic!" This is a sort of appeal to tradition fallacy, but some give it more weight because nature does it. Nature gave me a hernia. That's only good if you don't particularly like me. Which may be true, but still.

Slippery Slope 'The Camel's Nose' - if a claim is made that one thing will follow another, evidence must be presented for such. "Marijuana is a gateway drug." It's important to separate this from actual trend analysis - Elliquiy is getting a few hundred new signups a month as of this writing, it is not illogical to assume that there will be another three thousand over the course of the next year. It would, however, be illogical to assume that there would be three thousand active members then - or even twice the activity we have now.

Weak Analogy 'False Analogy', 'Faulty Analogy', 'Questionable Analogy' - an analogy that does not apply very strongly, if at all. Comparisons to Nazi Germany are often - but not always - weak analogies. It's important to remember that though no analogy is perfect, and all things have at least something in common, an analogy needs to serve a useful purpose.


Causal Fallacies

Non Causa Pro Causa - cause from no cause - refers to misunderstanding what, exactly, was the cause of a given event.

Regression Fallacy 'Regressive Fallacy' - people should not be surprised when normality reasserts itself. This can apply in the same manner that the Hot Hand Fallacy or Gambler's Fallacy does - and odd streak can be followed by a set of 'normal' results without explanation. However, this is more general, and has rather serious implications: suppose an ill person is pressured to try a homeopathic remedy. Eventually, they give in, and recover not long afterwards, because when at their sickest, their immune system is working its hardest, and would have recovered anyway. And if they don't recover, and they have a truly serious condition, well, dead people don't complain.

Questionable Cause - taking one event to be the cause of another without reason. "I should not have gone outside yesterday, I caught a cold." 'Colds' are suspected to be caused by the types of behavior that cold weather encourages, rather than cold weather itself.

Post Hoc Fallacy 'Post Hoc Ergo Propter Hoc', 'Confusing Coincidental Relationships With Causes' - a occurred before b, therefore a caused b. "I yawned, and saw a falling star. Yawning causes falling stars." Most superstitions are of this fallacy.

Texas Sharpshooter Fallacy 'To be certain of perfect aim, first shoot, then, call whatever you hit the target.' - this refers to actively looking for causes and assuming without evidence that a correlation to an event is the cause. "Cities have more factories in them, cities have a higher proportion of illness x, therefore factories are the cause of illness x."

Correlation does not imply causation 'Cum Hoc Ergo Propter Hoc', 'False Cause' - believing that because a occurs regularly with b, therefore a causes b. Includes Confusing Cause and Effect and Ignoring a Common Cause, but also pure coincidence - given enough sets of numbers, you will find one that matches what you are looking for.

Confusing Cause and Effect - wherein what is claimed to be the effect is actually the cause. Another take on the 'anger causes illness' example in the link could be 'staying in bed causes illness'. This can be difficult to work out properly, especially in feedback loops, or things like declaring whether the chicken or the egg came first.

Ignoring a Common Cause - where one event is taken to be caused by another when they were caused by a third event. Hail does not cause tornadoes, but rather the storm that makes them both.


Statistical Fallacies

Fake Precision 'Misplaced Precision', 'Spurious Accuracy' - new statistics with a surprising amount of accuracy likely deserve more scrutiny. "94.3 percent of women agree, soap tastes bad!" This sort of thing is generally used to make a claim seem far more substantial than it actually is.

Biased Sample 'Prejudiced Statistics', 'Loaded Statistics', 'Biased Induction', 'Biased Generalization' - how to lie with statistics 101. If you take a sample of a population (in the statistical sense - measuring the tide at various points during the day qualifies, for example), and it is flawed in some manner, the resulting statistics will likewise be flawed. Exit polls are a recently famous example of this - Republicans are more reluctant to answer them, biasing the sample. Of course, sometimes you want a biased sample - a poll of all women is fine so long as that is declared appropriately.

Hasty Generalization - using too small of a sample size in order to determine the nature of a whole. Asking one person's opinions on a thing is not sufficient to determine the opinions of the nation (though she may or may not have a keen insight into such), nor is testing one single grain of rice sufficient to determine the health of a batch. Note that a sample size of just one is fine for some purposes - we can safely assume a great deal about other stars by inspecting our own Sun, for example, especially stars of similar size, age, and metallicity.

For heterogeneous samples, the standard deviation sampling error is the square root of the sampling size. For example, one person is never representative of the whole, and you need four people to be two thirds certain that you are half right about a nation's political leanings, etc. Note that this is irrespective of the size of the whole, assuming that the sampling is truly random and that it's small compared to the whole - picking a thousand out of a billion still gives you only a 3.1% margin of error.

Misleading Vividness 'Anecdotal Fallacy' - a variation of hasty generalization in which a dramatic event is taken as evidence against more boring statistical results. Before IBM's 'deathstar' hard drive debacle, their laptops were considered by many to be the most reliable in the business, but even then some people will always have problems, occasionally disasters, and people are quite vocal about disasters they have suffered. Conversely, meeting two hot ladies at a beach in which you end up in a threesome with is not, on its own, a common event caused by going to the beach. If this has happened to you be aware that I am already jealous. Regardless, the detail or horror of a given fact has nothing to do with the likelihood of its occurrence.

Spotlight Fallacy "As seen on TV." - this fallacy occurs when media presentations are taken to be a representative sample. This is unfortunate for people who visit Minnesota outside of the winter months expecting it to be cold, and it turns out to be 90 degrees fahreinheit (~30 centigrade) outside, 100% humidity and all they have are sweaters.


False Exemptions

Special Pleading 'I/they am/are exempt' - is where an exception is made for a group or individual and no reasonable explanation is provided. "Polyamory should be outlawed, except for members of my religion." Note the Principle of Relevant Difference described in the link - the reason Special Pleading is a fallacy is because the exception has no logical basis. "Infants should not be fed honey, because the lack of aeration in their digestive tract permits botulism producing bacteria." This is not a fallacy because the reason is rooted in fact.

Relativist Fallacy 'Subjectivist Fallacy' - claiming that what is true for others is not true for you. "Your 'reality', sir, is nothing but lies and baldurdash and I am proud to say that I have no part of it whatsoever!" - to quote Baron Munchausen. This differs from special pleading in that no qualitative association is even given. Note that the relativist fallacy usually applies to objective truths - a contradiction invalidates a proof for everyone, whether or not they care for it to be invalidated.


Miscellany

Fallacy of Accident 'Dicto Simpliciter', 'Sweeping Generalization' - generalizations are not always appropriate. "Fish normally only breath water, lungfish and anabantoidei are fish, therefore they also can only breath water." These creatures are, in fact, able to breath air.

Argument from Ignorance 'ad ignorantiam', 'Appeal to ignorance', 'Burden of proof' - this fallacy occurs when you declare that because something cannot be proven false, it must therefore be true. "You can't prove there is no flying spaghetti monster, therefore he exists." This is a case of a false dilemma - it is possible for some things to be neither true nor false. A rule of thumb is that the burden of proof falls on the one making the positive assertion - to prove aliens exist, find me one, etc. However, it is not always clear which side has the burden of proof or if it even applies to a given debate.

Fallacy of Composition - stating that because a, b, and c have a given property, x, which contains a, b, and c, also has that property. "You are 75% water. Water is transparent. Therefore you are transparent," to make an obvious case. This is not always a fallacy - "Atoms are tangible due to electrostatic repulsion. You are made of atoms. Therefore you are tangible." This is perfectly logical, but it relies on unstated evidence - that  you are entirely made of atoms and that electromagnetic interaction is what allows you to be you in the first place, etc.

Fallacy of Division - claiming because x has a property, components a, b, and c also have that property. "You are not transparent, you are mostly water, therefore water is not transparent." As with this fallacy's opposite, composition, inferring common properties from the whole can be valid with justification.

False Dilemma 'Black & White Thinking' - wherein two options are presented and one is discredited when three or more options are in fact available. "We can't drink the sour milk, so we'll have to have orange juice today." When there is a perfectly good water faucet nearby, for example. The third option needs to be present in order for this to be a fallacy - you can either have read this paragraph or you haven't, but see also the excluded middle.

Middle Ground Fallacy 'Golden Mean Fallacy', 'Fallacy of Moderation' - just because a position is in between two extremes does not mean it is the right one. "On one hand, we can eradicate smallpox entirely. On the other, we can leave it alone. We should instead only eradicate half of all smallpox cases." To give another absurd example.

One Sidedness 'Card Stacking', 'Ignoring the Counterevidence', 'One-Sided Assessment', 'Slanting', 'Suppressed Evidence' - Fox News has a running gag where, when reporting on corrupt Republican elected officials - Ted Stevens, Larry Craig, etc. their party affiliation is referred to as Democrat instead of Republican. Ignoring the factual error, here, is the broader issue - presenting the case that all corrupt officials are Democrats, going so far as to alter the reporting of facts that might make it seem that Republicans, too, can be corrupt.

On a free forum, this is mostly a fallacy you commit against yourself. Anyone can present an opposing set of facts, but it can be an issue if facts themselves are being censored or glaringly omitted - by a media organization for example, or if you are trying to convince yourself of something.