Logical Fallacies

[leavingduetoboredom]

part of a good debate is not using logical fallacies and pointing them out to others so they understand why there argument is flawed, here is an explanation of logical fallacies

Description of Fallacies
In order to understand what a fallacy is, one must understand what an argument is. Very briefly, an argument consists of one or more premises and one conclusion. A premise is a statement (a sentence that is either true or false) that is offered in support of the claim being made, which is the conclusion (which is also a sentence that is either true or false).

There are two main types of arguments: deductive and inductive. A deductive argument is an argument such that the premises provide (or appear to provide) complete support for the conclusion. An inductive argument is an argument such that the premises provide (or appear to provide) some degree of support (but less than complete support) for the conclusion. If the premises actually provide the required degree of support for the conclusion, then the argument is a good one. A good deductive argument is known as a valid argument and is such that if all its premises are true, then its conclusion must be true. If all the argument is valid and actually has all true premises, then it is known as a sound argument. If it is invalid or has one or more false premises, it will be unsound. A good inductive argument is known as a strong (or "cogent" wink inductive argument. It is such that if the premises are true, the conclusion is likely to be true.

A fallacy is, very generally, an error in reasoning. This differs from a factual error, which is simply being wrong about the facts. To be more specific, a fallacy is an "argument" in which the premises given for the conclusion do not provide the needed degree of support. A deductive fallacy is a deductive argument that is invalid (it is such that it could have all true premises and still have a false conclusion). An inductive fallacy is less formal than a deductive fallacy. They are simply "arguments" which appear to be inductive arguments, but the premises do not provided enough support for the conclusion. In such cases, even if the premises were true, the conclusion would not be more likely to be true.



Examples of Fallacies

1.Inductive Argument
Premise 1: Most American cats are domestic house cats.
Premise 2: Bill is an American cat.
Conclusion: Bill is domestic house cat.


2.Factual Error
Columbus is the capital of the United States.


3.Deductive Fallacy
Premise 1: If Portland is the capital of Maine, then it is in Maine.
Premise 2: Portland is in Maine.
Conclusion: Portland is the capital of Maine.
(Portland is in Maine, but Augusta is the capital. Portland is the largest city in Maine, though.)


Inductive Fallacy
Premise 1: Having just arrived in Ohio, I saw a white squirrel.
Conclusion: All Ohio Squirrels are white.
(While there are many, many squirrels in Ohio, the white ones are very rare).


some common logical fallacies

Ad Hominem
Translated from Latin to English, "Ad Hominem" means "against the man" or "against the person."

An Ad Hominem is a general category of fallacies in which a claim or argument is rejected on the basis of some irrelevant fact about the author of or the person presenting the claim or argument. Typically, this fallacy involves two steps. First, an attack against the character of person making the claim, her circumstances, or her actions is made (or the character, circumstances, or actions of the person reporting the claim). Second, this attack is taken to be evidence against the claim or argument the person in question is making (or presenting). This type of "argument" has the following form:

Person A makes claim X.
Person B makes an attack on person A.
Therefore A's claim is false.

eg.
Bill: "I believe that abortion is morally wrong."
Dave: "Of course you would say that, you're a priest."
Bill: "What about the arguments I gave to support my position?"
Dave: "Those don't count. Like I said, you're a priest, so you have to say that abortion is wrong. Further, you are just a lackey to the Pope, so I can't believe what you say."

Straw Man
The Straw Man fallacy is committed when a person simply ignores a person's actual position and substitutes a distorted, exaggerated or misrepresented version of that position. This sort of "reasoning" has the following pattern:

Person A has position X.
Person B presents position Y (which is a distorted version of X).
Person B attacks position Y.
Therefore X is false/incorrect/flawed.
This sort of "reasoning" is fallacious because attacking a distorted version of a position simply does not constitute an attack on the position itself. One might as well expect an attack on a poor drawing of a person to hurt the person.
eg.
Bill and Jill are arguing about cleaning out their closets:
Jill: "We should clean out the closets. They are getting a bit messy."
Bill: "Why, we just went through those closets last year. Do we have to clean them out everyday?"
Jill: "I never said anything about cleaning them out every day. You just want too keep all your junk forever, which is just ridiculous."

(taken from http://www.nizkor.org/features/fallacies/ continued in next post)

[leavingduetoboredom]

Appeal to Authority
An Appeal to Authority is a fallacy with the following form:

Person A is (claimed to be) an authority on subject S.
Person A makes claim C about subject S.
Therefore, C is true.
This fallacy is committed when the person in question is not a legitimate authority on the subject. More formally, if person A is not qualified to make reliable claims in subject S, then the argument will be fallacious.

This sort of reasoning is fallacious when the person in question is not an expert. In such cases the reasoning is flawed because the fact that an unqualified person makes a claim does not provide any justification for the claim. The claim could be true, but the fact that an unqualified person made the claim does not provide any rational reason to accept the claim as true.

When a person falls prey to this fallacy, they are accepting a claim as true without there being adequate evidence to do so. More specifically, the person is accepting the claim because they erroneously believe that the person making the claim is a legitimate expert and hence that the claim is reasonable to accept. Since people have a tendency to believe authorities (and there are, in fact, good reasons to accept some claims made by authorities) this fallacy is a fairly common one.

Since this sort of reasoning is fallacious only when the person is not a legitimate authority in a particular context, it is necessary to provide some acceptable standards of assessment. The following standards are widely accepted:

The person has sufficient expertise in the subject matter in question
The claim being made by the person is within her area(s) of expertise
There is an adequate degree of agreement among the other experts in the subject in question
The person in question is not significantly biased
The area of expertise is a legitimate area or discipline
The authority in question must be identified.

eg.
Bill and Jane are arguing about the morality of abortion:
Bill: "I believe that abortion is morally acceptable. After all, a woman should have a right to her own body."
Jane: "I disagree completely. Dr. Johan Skarn says that abortion is always morally wrong, regardless of the situation. He has to be right, after all, he is a respected expert in his field."
Bill: "I've never heard of Dr. Skarn. Who is he?"
Jane: "He's the guy that won the Nobel Prize in physics for his work on cold fusion."
Bill: "I see. Does he have any expertise in morality or ethics?"
Jane: "I don't know. But he's a world famous expert, so I believe him


Appeal to fear
The Appeal to Fear is a fallacy with the following pattern:

Y is presented (a claim that is intended to produce fear).
Therefore claim X is true (a claim that is generally, but need not be, related to Y in some manner).
This line of "reasoning" is fallacious because creating fear in people does not constitute evidence for a claim.

It is important to distinguish between a rational reason to believe (RRB) (evidence) and a prudential reason to believe (PRB) (motivation). A RRB is evidence that objectively and logically supports the claim. A PRB is a reason to accept the belief because of some external factor (such as fear, a threat, or a benefit or harm that may stem from the belief) that is relevant to what a person values but is not relevant to the truth or falsity of the claim. For example, it might be prudent to not fail the son of your department chairperson because you fear he will make life tough for you. However, this does not provide evidence for the claim that the son deserves to pass the class.

Examples of Appeal to Fear

"You know, Professor Smith, I really need to get an A in this class. I'd like to stop by during your office hours later to discuss my grade. I'll be in your building anyways, visiting my father. He's your dean, by the way. I'll see you later."

"I don't think a Red Ryder BB rifle would make a good present for you. They are very dangerous and you'll put your eye out. Now, don't you agree that you should think of another gift idea?"


Guilt By Association
Guilt by Association is a fallacy in which a person rejects a claim simply because it is pointed out that people she dislikes accept the claim. This sort of "reasoning" has the following form:

It is pointed out that people person A does not like accept claim P.
Therefore P is false

It is clear that sort of "reasoning" is fallacious. For example the following is obviously a case of poor "reasoning": "You think that 1+1=2. But, Adolf Hitler, Charles Manson, Joseph Stalin, and Ted Bundy all believed that 1+1=2. So, you shouldn't believe it."

The fallacy draws its power from the fact that people do not like to be associated with people they dislike. Hence, if it is shown that a person shares a belief with people he dislikes he might be influenced into rejecting that belief. In such cases the person will be rejecting the claim based on how he thinks or feels about the people who hold it and because he does not want to be associated with such people.

Of course, the fact that someone does not want to be associated with people she dislikes does not justify the rejection of any claim. For example, most wicked and terrible people accept that the earth revolves around the sun and that lead is heavier than helium. No sane person would reject these claims simply because this would put them in the company of people they dislike (or even hate).

Examples of Guilt By Association

Will and Kiteena are arguing over socialism. Kiteena is a pacifist and hates violence and violent people.
Kiteena: "I think that the United States should continue to adopt socialist programs. For example, I think that the government should take control of vital industries."
Will: "So, you are for state ownership of industry."
Kiteena: "Certainly. It is a great idea and will help make the world a less violent place."
Will: "Well, you know Stalin also endorsed state ownership on industry. At last count he wiped out millions of his own people. Pol Pot of Cambodia was also for state ownership of industry. He also killed millions of his own people. The leadership of China is for state owned industry. They killed their own people in that square. So, are you still for state ownership of industry?"
Kiteena: "Oh, no! I don't want to be associated with those butchers!"

special pleeding
Special Pleading is a fallacy in which a person applies standards, principles, rules, etc. to others while taking herself (or those she has a special interest in) to be exempt, without providing adequate justification for the exemption. This sort of "reasoning" has the following form:

Person A accepts standard(s) S and applies them to others in circumtance(s) C.
Person A is in circumstance(s) C.
Therefore A is exempt from S.
The person committing Special Pleading is claiming that he is exempt from certain principles or standards yet he provides no good reason for his exemption. That this sort of reasoning is fallacious is shown by the following extreme example:

Barbara accepts that all murderers should be punished for their crimes.
Although she murdered Bill, Barbara claims she is an exception because she really would not like going to prison.
Therefore, the standard of punishing murderers should not be applied to her.
This is obviously a blatant case of special pleading. Since no one likes going to prison, this cannot justify the claim that Barbara alone should be exempt from punishment.

Examples of Special Pleading

Bill and Jill are married. Both Bill and Jill have put in a full day at the office. Their dog, Rover, has knocked over all the plants in one room and has strewn the dirt all over the carpet. When they return, Bill tells Jill that it is her job to clean up after the dog. When she protests, he says that he has put in a full day at the office and is too tired to clean up after the dog.

Jane and Sue share a dorm room.
Jane: "Turn of that stupid stereo, I want to take a nap."
Sue: "Why should I? What are you exhausted or something?"
Jane: "No, I just feel like taking a nap."
Sue: "Well, I feel like playing my stereo."
Jane: "Well, I'm taking my nap. You have to turn your stereo off and that's final."

still more to come

[leavingduetoboredom]

Ignoring a Common Cause (also known as Questionable Cause) This fallacy has the following general structure:

A and B are regularly connected (but no third, common cause is looked for).
Therefore A is the cause of B.
This fallacy is committed when it is concluded that one thing causes another simply because they are regularly associated. More formally, this fallacy is committed when it is concluded that A is the cause of B simply because A and B are regularly connected. Further, the causal conclusion is drawn without considering the possibility that a third factor might be the cause of both A and B.

In many cases, the fallacy is quite evident. For example, if a person claimed that a person's sneezing was caused by her watery eyes and he simply ignored the fact that the woman was standing in a hay field, he would have fallen prey to the fallacy of ignoring a common cause. In this case, it would be reasonable to conclude that the woman's sneezing and watering eyes was caused by an allergic reaction of some kind. In other cases, it is not as evident that the fallacy is being comitted. For example, a doctor might find a large amount of bacteria in one of her patients and conclude that the bacteria are the cause of the patient's illness. However, it might turn out that the bacteria are actually harmless and that a virus is weakening the person, Thus, the viruses would be the actual cause of the illness and growth of the bacteria (the viruses would weaken the ability of the person's body to resist the growth of the bacteria).

As noted in the discussion of other causal fallacies, causality is a rather difficult matter. However, it is possible to avoid this fallacy by taking due care. In the case of Ignoring a Common Cause, the key to avoiding this fallacy is to be careful to check for other factors that might be the actual cause of both the suspected cause and the suspected effect. If a person fails to check for the possibility of a common cause, then they will commit this fallacy. Thus, it is always a good idea to always ask "could there be a third factor that is actually causing both A and B?"

Examples of Ignoring a Common Cause

One day Bill wakes up with a fever. A few hours later he finds red spots on his skin. he concludes that the fever must have caused the red spots. His friend insists that the spots and the fever are caused by some microbe. Bill laughs at this and insists that if he spends the day in a tub of cold water his spots will go away.

Over the course of several weeks the needles from the pine trees along the Wombat river fell into the water. Shortly thereafter, many dead fish washed up on the river banks. When the EPA investigated, the owners of the Wombat River Chemical Company claimed that is it was obvious that the pine needles had killed the fish. Many local environmentalists claimed that the chemical plant's toxic wastes caused both the trees and the fish to die and that the pine needles had no real effect on the fish.


Appeal to Common Practice
The Appeal to Common Practice is a fallacy with the following structure:

X is a common action.
Therefore X is correct/moral/justified/reasonable, etc.
The basic idea behind the fallacy is that the fact that most people do X is used as "evidence" to support the action or practice. It is a fallacy because the mere fact that most people do something does not make it correct, moral, justified, or reasonable.

An appeal to fair play, which might seem to be an appeal to common practice, need not be a fallacy. For example, a woman working in an office might say "the men who do the same job as me get paid more than I do, so it would be right for me to get paid the same as them." This would not be a fallacy as long as there was no relevant difference between her and the men (in terms of ability, experience, hours worked, etc.). More formally:

It is common practice to treat people of type Y in manner X and to treat people of type Z in a different manner.
There is no relevant difference between people of type Y and type Z.
Therefore people of type Z should be treated in manner X, too.
This argument rests heavily on the principle of relevant difference. On this principle two people, A and B, can only be treated differently if and only if there is a relevant difference between them. For example, it would be fine for me to give a better grade to A than B if A did better work than B. However, it would be wrong of me to give A a better grade than B simply because A has red hair and B has blonde hair.

There might be some cases in which the fact that most people accept X as moral entails that X is moral. For example, one view of morality is that morality is relative to the practices of a culture, time, person, etc. If what is moral is determined by what is commonly practiced, then this argument:

Most people do X.
Therefore X is morally correct.
would not be a fallacy. This would however entail some odd results. For example, imagine that thereare only 100 people on earth. 60 of them do not steal or cheat and 40 do. At this time, stealing and cheating would be wrong. The next day, a natural disaster kills 30 of the 60 people who do not cheat or steal. Now it is morally correct to cheat and steal. Thus, it would be possible to change the moral order of the world to one's view simply by eliminating those who disagree.

Examples of Appeal to Common Practice

Director Jones is in charge of running a state waste management program. When it is found that the program is rife with corruption, Jones says "This program has its problems, but nothing goes on in this program that doesn't go on in all state programs."

"Yeah, I know some people say that cheating on tests is wrong. But we all know that everyone does it, so it's okay."

"Sure, some people buy into that equality crap. However, we know that everyone pays women less then men. It's okay, too. Since everyone does it, it can't really be wrong."


Description of Begging the Question (also known as Circular Reasoning)Begging the Question is a fallacy in which the premises include the claim that the conclusion is true or (directly or indirectly) assume that the conclusion is true. This sort of "reasoning" typically has the following form.

Premises in which the truth of the conclusion is claimed or the truth of the conclusion is assumed (either directly or indirectly).
Claim C (the conclusion) is true.
This sort of "reasoning" is fallacious because simply assuming that the conclusion is true (directly or indirectly) in the premises does not constitute evidence for that conclusion. Obviously, simply assuming a claim is true does not serve as evidence for that claim. This is especially clear in particularly blatant cases: "X is true. The evidence for this claim is that X is true."

Some cases of question begging are fairly blatant, while others can be extremely subtle.

Examples of Begging the Question

Bill: "God must exist."
Jill: "How do you know."
Bill: "Because the Bible says so."
Jill: "Why should I believe the Bible?"
Bill: "Because the Bible was written by God."

"If such actions were not illegal, then they would not be prohibited by the law."

"The belief in God is universal. After all, everyone believes in God."

Interviewer: "Your resume looks impressive but I need another reference."
Bill: "Jill can give me a good reference."
Interviewer: "Good. But how do I know that Jill is trustworthy?"
Bill: "Certainly. I can vouch for her."

Ad Hominem Tu Quoque
This fallacy is committed when it is concluded that a person's claim is false because 1) it is inconsistent with something else a person has said or 2) what a person says is inconsistent with her actions. This type of "argument" has the following form:

Person A makes claim X.
Person B asserts that A's actions or past claims are inconsistent with the truth of claim X.
Therefore X is false.
The fact that a person makes inconsistent claims does not make any particular claim he makes false (although of any pair of inconsistent claims only one can be true - but both can be false). Also, the fact that a person's claims are not consistent with his actions might indicate that the person is a hypocrite but this does not prove his claims are false.

Examples of Ad Hominem Tu Quoque

Bill: "Smoking is very unhealthy and leads to all sorts of problems. So take my advice and never start."
Jill: "Well, I certainly don't want to get cancer."
Bill: "I'm going to get a smoke. Want to join me Dave?"
Jill: "Well, I guess smoking can't be that bad. After all, Bill smokes."

Jill: "I think the gun control bill shouldn't be supported because it won't be effective and will waste money."
Bill: "Well, just last month you supported the bill. So I guess you're wrong now."

Peter: "Based on the arguments I have presented, it is evident that it is morally wrong to use animals for food or clothing."
Bill: "But you are wearing a leather jacket and you have a roast beef sandwich in your hand! How can you say that using animals for food and clothing is wrong!"

Argumentum ad ignorantiam (also known as argument from ignorance)
Argumentum ad ignorantiam means "argument from ignorance." The fallacy occurs when it's argued that something must be true, simply because it hasn't been proved false. Or, equivalently, when it is argued that something must be false because it hasn't been proved true.

(Note that this isn't the same as assuming something is false until it has been proved true. In law, for example, you're generally assumed innocent until proven guilty.)

Here are a couple of examples:

"Of course the Bible is true. Nobody can prove otherwise."

"Of course telepathy and other psychic phenomena do not exist. Nobody has shown any proof that they are real."

In scientific investigation, if it is known that an event would produce certain evidence of its having occurred, the absence of such evidence can validly be used to infer that the event didn't occur. It does not prove it with certainty, however.

For example:

"A flood as described in the Bible would require an enormous volume of water to be present on the earth. The earth doesn't have a tenth as much water, even if we count that which is frozen into ice at the poles. Therefore no such flood occurred."

It is, of course, possible that some unknown process occurred to remove the water. Good science would then demand a plausible testable theory to explain how it vanished.

[leavingduetoboredom]

Non sequitur
A non sequitur is an argument where the conclusion is drawn from premises which aren't logically connected with it. For example:

"Since Egyptians did so much excavation to construct the pyramids, they were well versed in paleontology."

(Non sequiturs are an important ingredient in a lot of humor. They're still fallacies, though.)


Plurium interrogationum / Many questions
This fallacy occurs when someone demands a simple (or simplistic) answer to a complex question.

"Are higher taxes an impediment to business or not? Yes or no?"
Red herring
This fallacy is committed when someone introduces irrelevant material to the issue being discussed, so that everyone's attention is diverted away from the points made, towards a different conclusion.

"You may claim that the death penalty is an ineffective deterrent against crime -- but what about the victims of crime? How do you think surviving family members feel when they see the man who murdered their son kept in prison at their expense? Is it right that they should pay for their son's murderer to be fed and housed?"


Reification / Hypostatization
Reification occurs when an abstract concept is treated as a concrete thing.

"I noticed you described him as 'evil'. Where does this 'evil' exist within the brain? You can't show it to me, so I claim it doesn't exist, and no man is 'evil'."


Shifting the burden of proof
The burden of proof is always on the person asserting something. Shifting the burden of proof, a special case of Argumentum ad Ignorantiam, is the fallacy of putting the burden of proof on the person who denies or questions the assertion. The source of the fallacy is the assumption that something is true unless proven otherwise.

For further discussion of this idea, see the "Introduction to Atheism" document.

"OK, so if you don't think the grey aliens have gained control of the US government, can you prove it?"


The slippery slope argument
This argument states that should one event occur, so will other harmful events. There is no proof made that the harmful events are caused by the first event. For example:

"If we legalize marijuana, then more people would start to take crack and heroin, and we'd have to legalize those too. Before long we'd have a nation full of drug-addicts on welfare. Therefore we cannot legalize marijuana."


Denial of the antecedent
This fallacy is an argument of the form "A implies B, A is false, therefore B is false." The truth table for implication makes it clear why this is a fallacy.

Note that this fallacy is different from Non Causa Pro Causa. That has the form "A implies B, A is false, therefore B is false", where A does not in fact imply B at all. Here, the problem isn't that the implication is invalid; rather it's that the falseness of A doesn't allow us to deduce anything about B.

"If the God of the Bible appeared to me, personally, that would certainly prove that Christianity was true. But God has never appeared to me, so the Bible must be a work of fiction."


Affirmation of the consequent
This fallacy is an argument of the form "A implies B, B is true, therefore A is true." To understand why it is a fallacy, examine the truth table for implication given earlier. Here's an example:

"If the universe had been created by a supernatural being, we would see order and organization everywhere. And we do see order, not randomness -- so it's clear that the universe had a creator."

(taken from here)

[leavingduetoboredom]

top 20 most common logical fallacies

1. Ad hominem An ad hominem argument is any that attempts to counter anothers claims or conclusions by attacking the person, rather than addressing the argument itself. True believers will often commit this fallacy by countering the arguments of skeptics by stating that skeptics are closed minded. Skeptics, on the other hand, may fall into the trap of dismissing the claims of UFO believers, for example, by stating that people who believe in UFO's are crazy or stupid.
2. Ad ignorantum The argument from ignorance basically states that a specific belief is true because we don't know that it isn't true. Defenders of extrasensory perception, for example, will often overemphasize how much we do not know about the human brain. UFO proponents will often argue that an object sighted in the sky is unknown, and therefore it is an alien spacecraft.
3. Argument from authority Stating that a claim is true because a person or group of perceived authority says it is true. Often this argument is implied by emphasizing the many years of experience, or the formal degrees held by the individual making a specific claim. It is reasonable to give more credence to the claims of those with the proper background, education, and credentials, or to be suspicious of the claims of someone making authoritative statements in an area for which they cannot demonstrate expertise. But the truth of a claim should ultimately rest on logic and evidence, not the authority of the person promoting it.
4. Argument from final Consequences Such arguments (also called teleological) are based on a reversal of cause and effect, because they argue that something is caused by the ultimate effect that it has, or purpose that is serves. For example: God must exist, because otherwise life would have no meaning.
5. Argument from Personal Incredulity I cannot explain or understand this, therefore it cannot be true. Creationists are fond of arguing that they cannot imagine the complexity of life resulting from blind evolution, but that does not mean life did not evolve.
6. Confusing association with causation This is similar to the post-hoc fallacy in that it assumes cause and effect for two variables simply cause they are correlated, although the relationship here is not strictly that of one variable following the other in time. This fallacy is often used to give a statistical correlation a causal interpretation. For example, during the 1990’s both religious attendance and illegal drug use have been on the rise. It would be a fallacy to conclude that therefore, religious attendance causes illegal drug use. It is also possible that drug use leads to an increase in religious attendance, or that both drug use and religious attendance are increased by a third variable, such as an increase in societal unrest. It is also possible that both variables are independent of one another, and it is mere coincidence that they are both increasing at the same time. A corollary to this is the invocation of this logical fallacy to argue that an association does not represent causation, rather it is more accurate to say that correlation does not necessarily mean causation, but it can. Also, multiple independent correlations can point reliably to a causation, and is a reasonable line of argument.
7. Confusing currently unexplained with unexplainable Because we do not currently have an adequate explanation for a phenomenon does not mean that it is forever unexplainable, or that it therefore defies the laws of nature or requires a paranormal explanation. An example of this is the "God of the Gapsâ" strategy of creationists that whatever we cannot currently explain is unexplainable and was therefore an act of god.
8. False Continuum The idea that because there is no definitive demarcation line between two extremes, that the distinction between the extremes is not real or meaningful: There is a fuzzy line between cults and religion, therefore they are really the same thing.
9. False Dichotomy Arbitrarily reducing a set of many possibilities to only two. For example, evolution is not possible, therefore we must have been created (assumes these are the only two possibilities). This fallacy can also be used to oversimplify a continuum of variation to two black and white choices. For example, science and pseudoscience are not two discrete entities, but rather the methods and claims of all those who attempt to explain reality fall along a continuum from one extreme to the other.
10. Inconsistency Applying criteria or rules to one belief, claim, argument, or position but not to others. For example, some consumer advocates argue that we need stronger regulation of prescription drugs to ensure their safety and effectiveness, but at the same time argue that medicinal herbs should be sold with no regulation for either safety or effectiveness.
11. The Moving Goalpost A method of denial arbitrarily moving the criteria for "proof" or acceptance out of range of whatever evidence currently exists.
12. Non-Sequitur In Latin this term translates to "doesn't follow". This refers to an argument in which the conclusion does not necessarily follow from the premises. In other words, a logical connection is implied where none exists.
13. Post-hoc ergo propter hoc This fallacy follows the basic format of: A preceded B, therefore A caused B, and therefore assumes cause and effect for two events just because they are temporally related (the latin translates to "after this, therefore because of this" wink .
14. Reductio ad absurdum These arguments assume that if an argument is valid, it necessarily means that the most extreme example of that argument must also be valid. A UFO enthusiast once argued that if I am skeptical about the existence of alien visitors, I must also be skeptical of the existence of the Great Wall of China, since I have not personally seen either. He therefore tried to take my skepticism to an absurd extreme in order to invalidate any skepticism.
15. Slippery Slope This logical fallacy is the argument that a position is not consistent or tenable because accepting the position means that the extreme of the position must also be accepted. But moderate positions do not necessarily lead down the slippery slope to the extreme.
16. Straw Man Arguing against a position which you create specifically to be easy to argue against, rather than the position actually held by those who oppose your point of view.
17. Special pleading, or ad-hoc reasoning This is a subtle fallacy which is often difficult to recognize. In essence, it is the arbitrary introduction of new elements into an argument in order to fix them so that they appear valid. A good example of this is the ad-hoc dismissal of negative test results. For example, one might point out that ESP has never been demonstrated under adequate test conditions, therefore ESP is not a genuine phenomenon. Defenders of ESP have attempted to counter this argument by introducing the arbitrary premise that ESP does not work in the presence of skeptics. This fallacy is often taken to ridiculous extremes, and more and more bizarre ad hoc elements are added to explain experimental failures or logical inconsistencies.
18. Tautology A tautology is an argument that utilizes circular reasoning, which means that the conclusion is also its own premise. The structure of such arguments is A=B therefore A=B, although the premise and conclusion might be formulated differently so it is not immediately apparent as such. For example, saying that therapeutic touch works because it manipulates the life force is a tautology because the definition of therapeutic touch is the alleged manipulation (without touching) of the life force.
19. Tu quoque Literally, you too. This is an attempt to justify wrong action because someone else also does it. "My evidence may be invalid, but so is yours."
20. Unstated Major Premise This fallacy occurs when one makes an argument which assumes a premise which is not explicitly stated. For example, arguing that we should label food products with their cholesterol content because Americans have high cholesterol assumes that: 1) cholesterol in food causes high serum cholesterol; 2) labeling will reduce consumption of cholesterol; and 3) that having a high serum cholesterol is unhealthy. This fallacy is also sometimes called begging the question

(taken from the skepticks guide to the universe, i recomend checking them out, they do a really good critical thinking podcast, and compleatly debumk most pseudo-science(sp) etc. very interesting)

[leavingduetoboredom]

The following fallacies are one that users on gaia have pointed out to me that i missed in my orignal posts, this is just my way of thanking them and giving credit were credit is due

Populum Fallacy
It occurs whenever a conclusion is drawn, or invited to be drawn on the basis of a popular belief. There's two types:

Boosterism: A person's premisses are tailored specifically to appeal the sentiments or prejudices of those whom the argument is intended to persuade.

Popularity: Attempts to appeal inappropriately to so-called "common knowledge," which may not be knowledge at all.
((credit to Chiisana_Inori))

Argument from fallacy (or argumentum ad logicam)
The argument from fallacy, also known as argumentum ad logicam or fallacy fallacy, is a logical fallacy which assumes that because an argument is fallacious then its conclusion must be false.

It has the general argument form:

If P, then Q.
P is a fallacious argument.
Therefore, Q is false.
For example:

When I let go of this pencil, supposedly Angels from Heaven on high will push it downward. Therefore, it will accelerate towards the ground at 9.80665 meters per second squared. Angels don't exist, because of (proof). Therefore, the pencil will not fall when I release it.
Even if you could disprove that angels will exert downward pressure on your pencil, it would not follow that if you let go of the pencil then it would not fall to the ground. It just means that "angel theory" is not a sound way of reaching that conclusion, regardless of the conclusion's truth or falsity. The pencil will still fall, even if it has been proven that Angels are not the ones that make it fall.

Other Examples:

Anne: "All cats are animals. Ginger is an animal. This means Ginger is a cat.".
Bill: "Ah you just committed the affirming the consequent logical fallacy. Sorry, you are wrong, which means that Ginger is not a cat". (But of course, while it is not certain that Ginger is a cat, Ginger might be one.)
Anne: "OK — I'll prove I'm English — I speak English so that proves it".
Bill: "But Americans speak English too. You have committed the package-deal fallacy, speaking English and being English don't always go together. That means you are not English".
Showing that arguments given for a position are fallacies does not disprove the position. It may, nevertheless, be correct; the argument merely should not compel anyone to believe, either way.
((credit to Blaze-kun for mentioning it it and also to wikipedia))

[leavingduetoboredom]

Usefull Links

http://www.vandruff.com/art_converse.html
(thanks to Blaze-cun)
A good site, has a lot of exampels of how Ad hominem is used as well as some other fallacies and variations on each of them, i advise having a look at it

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ninja

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reserved

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reserved