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logical fallicies

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Brandice Snowden

on 4 May 2010

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Transcript of logical fallicies

Ad hominem Ad hominem Rather than addressing the argument at hand, the person engaging in this fallacy instead personally attacks the opposing party.

Example Argument:

Argument: “UFOs exist and they may come from other worlds.”

Fallacy: “You are crazy and should be locked up.”

Ad ignorantiam This is an argument from ignorance, stating that a belief is true because we can’t disprove it. It’s often made as a leap of reasoning where a person will skip a couple of necessary steps in order to come to their conclusion.

Example Argument:

Argument: “UFOs are unidentified flying objects. Not even the military can tell what some of them are.”

Fallacy: “Since UFOs are unidentified, they must be from other worlds.”

Argument: “How do you know they are from other worlds?”

Fallacy: “How do you know they aren’t?”

Argument from authority This happens when a statement form an authority figure on any given subject is expected to be taken as completely true. You may be more likely to trust someone with a degree or years of experience within a certain field, than someone with little background on what they’re speaking about. However, the truth of their claims should ultimately rest on the logic and evidence presented rather than the deliverer’s authority.

Example Argument:

Fallacy: John Smith (PhD, BFA, LMNOP…) : “Acupuncture works!”

Argument: “What evidence do you have to back up this claim?”

Fallacy: “Do you see how many letters are after my name? Trust me!”

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.

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.

Confusing association with causation

This is similar to the post-hoc fallacy in that it assumes cause and effect for two variables simply because 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.

Confusing association with causation

This is similar to the post-hoc fallacy in that it assumes cause and effect for two variables simply because 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.

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.

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.

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.

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.

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”).

Reductio ad absurdum

In formal logic, the reductio ad absurdum is a legitimate argument. It follows the form that if the premises are assumed to be true it necessarily leads to an absurd (false) conclusion and therefore one or more premises must be false. The term is now often used to refer to the abuse of this style of argument, by stretching the logic in order to force an absurd conclusion. For example 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. This is a false reductio ad absurdum because he is ignoring evidence other than personal eyewitness evidence, and also logical inference. In short, being skeptical of UFO’s does not require rejecting the existence of the Great Wall.

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.

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.

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.

Tautology

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.

The Moving Goalpost

A method of denial arbitrarily moving the criteria for “proof” or acceptance out of range of whatever evidence currently exists.

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.”

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.

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