People often fall into these logic holes not by purpose or fault but more often by hazardous occupation, grabbing the nearest most dangerous looking rock and going "over the top" onto the no man's land of debate having not properly prepared for it, and instead just launching into the debate in self-assured confidence that they are right, no matter how small the rock they are holding, or what form of wall they are attempting to use it against.
Most people wake out of this self-assured haze of committing these hasty logic-farts after about a year of being incontrovertibly destroyed on the debate forums/chat shows/radio/facebook groups. Some choose to ignore polite suggestions and then volunteer to not care about these problems, then they are falling into these holes quite by repetition, almost intentionally.
Here is my attempt to detail some of the most significant and frequent logical fallacies I have encountered.
-Bare Assertion fallacy:
The premise that something must be true purely because it says it is true. Most frequently seen with fundamentalist religious groups.
-The Negative Proof fallacy
This would go in the favourites list because it is a frequent goody, and is easy to spot. Negative proof fallacy is when someone making a theory or claim fails to produce just reasoning or evidence for their claim. In response to any criticism or request for evidence they fail to mount a defensive account of their reasoning or evidence, preferring instead to attack the critic as having no evidence for the criticism. This is a disgusting abuse of logical argument, and a savage lack of tact on the person making the claim's behalf.
X: I propose theory
Y: How can you possibly say that??
X: Prove it is false then
Response; X hasn't provided evidence that it is true.
This is absurd because evidence cannot be provided against something which does not exist. Arguments cannot be made out of negative evidence (lack of evidence to the contrary), therefore evidence is the burden of the original claims.
This is where someone reduces the situation beyond Occam's razor should allow - down to two positions; their own, and the oppositions (or a false version of it) - and argue that either one of these is correct, or the other is. This is often used when someone commits a negative evidence fallacy, instead of providing evidence they wish to try de construct the opposition's evidence, and in doing so conclude their position is correct because it is the "only" alternative.
De constructing something does not prove its alternative correct, it only proves that which is proven false, to be false. It's not that hard to understand when you say it that simply, but people manage to find it so.
-Equivocation/False Attribution Fallacy
This is the misleading use of a term or concept with more than one meaning. A common example I've heard;
A feather is light.
What is light cannot be dark.
Therefore, a feather cannot be dark.
Often accompanied by sarcasm and a sense of finality, as though the person committing the fallacy has just achieved a feat of reasoning and won the argument.
-Perfect Solution/Nirvana Fallacy
This is the idea that a perfect solution exists, therefore any potential solution which is not perfect is therefore false. This has often been applied to the theory of evolution whereby parts of it have been discredited, edited or adjusted over the years, and it does not explain many things, such as love, morality or the origin of life - ergo the fallacy is made; "it is not perfect, therefore it is false".
-Begging the question
Begging the question is related to the fallacy known as circular argument, vicious circle or circular reasoning. This was first pointed out by the famous Greek Philosopher Aristotle who focused heavily on forms of logical thinking.
This is where a conclusion is drawn from a weak premise.Well described in wikipedia: "In popular usage, "begging the question" is often used to mean that a statement invites another obvious question. This usage is disparaged."
-Post hoc ergo propter hoc
Latin for "after this, therefore because of this". This is where two events, one observed after another are concluded to be related simply from the chronology of their appearance, and not by any actual connection or mechanism that is accounted for. This is a problem very frequently made in pseudo-science, and even amateur science student projects.
Two events are not necessarily related by their chronological appearance, however repetitive observation of such a correlation after repetition of the supposed causality, will hint to a relationship being empirically present, but the relation should be accounted for deeper than the statistic.
Is an argument where the author attempts to better their position by inappropriately trying to discredit their opponents, for example suggesting that they are stupid, childish, ignorant or foolish and carrying that no-one would listen to a stupid childish ignorant fool.
-Straw man/appeal to ridicule
A straw man argument is one I see less of these days. This is where the attempt is made to discredit something by misrepresenting its claims, reasons or conclusions and mocking the fake or "straw man" image instead. One cannot defend a straw man attack other than to point out what it is, because one cannot defend a deliberately ridiculous image of themself. An example;
If relativity was right, my car would get shorter and heavier when I drive it. This is absurd, therefore relativity must be false.
Straw man can also take the form of an Ad Hominem.
-Ad Nauseam/argumentum ad infinitum
This is an argument made repeatedly (possibly by different people) irrelevant of responses until nobody cares to discuss it anymore. Most logical fallacies are often Ad Nauseam on top of their initial faults, on account of the theorist having stuck soft cheese in their ears.
My personal favourites;
This is where someone cherry-picks a quote from someone, most often from the opposition of the debate that in the sentence quote alone claims the opposition opinion or status to be false. The problem is the entire paragraph or piece of text from which the quote is taken can often be found to be an example of objections to their work/claims - and move on to discuss the objections the author understands to arise.
The most often quote-mine I see used is that of Charles Darwin's discussion of the eye. You can see a perfect and awkward example of it being patiently picked here.
-Reductio Ad Hitlerum;
Form of an Ad Hominem. Equivocating your opponent with, or blaming your opponent's position on having been the prime responsibility for Hiter, Stalin and other historical nasties. As if comparing your opponent to someone else who is evil is going to make the logical problems float away. Most frequent sightings of this logic-fart are in evolution vs creationism debates.
Response: There are many flaws in this argument, most notably that said parties used and savagely distorted views from BOTH sides of this debate, aswell as other reasons not related to the conversation. Just about everyone can agree these men were evil and crazy, and do not represent anyone here.
It already has its own definition, but the better one for creationists and conspiracy theorists alike is one that Eugene Smit has worked out.
If a lot of people are in a group and share the same opinions, usually group-think means that anyone in the group with opinions that would not be shared by the group, will decide not to share them in order to support the group's stability. This works in reverse with these discussions, where anyone in a group expressing obscene or badly made arguments in a group that is not shared by the group - the group will say nothing, and allow it, because he's an ally.
If someone attacks the speaker on his claimed opinions, other members of the group who would not have made such a claim in the first place, and do not necessarily agree with them, will rush in to the claimant's defence, and go on a group attack on the outsider who's pointing out the problem with the one member's comments. A suitable slogan for this one is "Strength in numbers."
Response: If someone who holds similar opinions to you says something irrational, immoral or absurd; don't be afraid to tell them so, and definately don't pick up their comments that you don't agree with - against someone else, that's just stupid.
Another one pointed out by Eugene. Double-think is a gift from George Orwell, which becomes ironic when conspiracy theorists commit this fallacy, having held Orwell as a hero, in the process, they can quite often commit Orwell's "double-think".
Double-think is where a person is able to take two completely contradictory viewpoints, and simultaneously accept both of them.
Example; using a form of logic to dismiss your opponent, but objecting when the same logic is applied to something you would hold to, even if it's in correct context. The logic is not false, because it's mine, and it's logic. Therefor the opponent must be wrong.
Another example; Claiming to hold a solid scientific position with scientific evidence, then when questioned for said evidence, invoke spirituality, or imply the nature of your claims to be ethereal and spiritual, and the opponent has "a closed mind".
I have seen these committed quite a lot, even a few from my "personal favourites" list, but mostly from the "basics" list. For a complete list see the wikipedia article on fallacious reasoning.
The final one to add here is not to overuse the discovery of a logical fallacies as the final nail in this coffin is the ...
-Argument from fallacy
This is where an argument has been suggested that creates a logical fallacy itself, and the argument against its conclusion is that because its argument is a fallacious one, its conclusion is false. This is important for everyone to understand. Just because an argument is a false one, the conclusion it is reaching to may not be false. You can take anything true and make a false argument for it, the falsehood of the argument does not carry to the conclusion. Only if a conclusion has nothing but false arguments for it can you confidently doubt the conclusion.