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.
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.
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.
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 FallaciesFake 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 ExemptionsSpecial 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.
MiscellanyFallacy 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.