# 21 Common logic errors

1. Ad Hominem Argument An argument that counters another’s claim or conclusion by attacking the person, rather than attacking the argument itself. (Latin, “against the man.”) A specific example of the Genetic Fallacy which assumes that an idea is not true because of its origin. E.g., a Democrat (or Republican) has a idea, therefore, it must be bad. (Also called the Fallacy of Irrelevance.)

2. Argument from Antiquity An argument is true because it has been held for a long time. Related to the Argument from Numbers, the argument that because many people think something is true, it is true (also known as the Argument Ad Populum).

3. Argument from Authority Stating that a claim is true because an authority (person or group of people) says it is true.

4. Argument from Final Consequences A claim is true because of a purpose or outcome that is served (or vice versa). Also known as a Teleological Argument. E.g., “evolution cannot be true because accepting it will lead to immorality.”

5. Argument from Ignorance The claim that a specific belief is true because we don’t know that it isn’t true.

6. Argument from Personal Incredulity Because you, personally, cannot understand or accept a proposition it is, therefore, not true. Often coupled with a False Dichotomy (see below) as in “I don’t see how the eye could have evolved, therefore, God did it.”

7. Begging the Question or a Tautology A statement that hinges on A=A (or A=B therefore B=A), which is simply restating the premise. For example, “he is unintelligent because he is stupid” or “only a criminal would commit a crime; the fact that criminals commit crimes is proof of this.” (Tautology, literally a repetition.) The “proof” is a restatement of the premise.

8. Confirmation Bias Noticing only the facts that support your thesis but ignoring those that do not.

9. Confusing Correlation with Causation Assuming cause and effect for two variables because they are correlated. E.g., “heroin addicts drank milk as a child, therefore, milk causes heroin addiction.” This is similar to the Post-hoc Ergo Propter Hoc fallacy (see below).

10. Confounding the Unexplained with the Unexplainable Because we do not currently have an explanation for a phenomenon does not mean that it is forever unexplainable or that it requires a paranormal/supernatural explanation.

11. False Continuum The idea that because there is no definitive demarcation between two extremes, the distinction between the extremes is not real or meaningful. E.g, because there is a fuzzy line between science and pseudoscience they are the same thing. Related to the Slippery Slope (see below).

12. False Dichotomy Arbitrarily reducing a set of possibilities to only two.

13. False Premise An incorrect/untrue underlying assumption. Often found in an argument that is otherwise logically consistent but which leads to a false conclusion.

14. Inconsistency Applying specific criteria or rules to one belief, claim, argument, or position but not to others.

15. Moving the Goalpost A method of denial by arbitrarily moving the criteria for proof, acceptance, or rejection out of the range of whatever evidence currently exists or is agreed upon.

16. Non-Sequitur This refers to an argument in which the conclusion does not follow from the premise. In other words, a logical connection is implied where none exists. (Latin, “doesn’t follow.”). Really, all logical fallacies are non-sequiturs.

17. Post-hoc Ergo Propter Hoc This fallacy follows the basic form of: A preceded B, therefore A caused B. This argument assumes cause and effect for two events just because they are temporally related. (Latin, “after this, therefore because of this.”)

18. Slippery Slope The argument that a position is not acceptable because accepting the position means that the extreme of the position must also be accepted. But, moderate positions do not necessarily lead down a slippery slope to the extreme. Careful here: Reductio Ad Absurdum (Latin: "reduction to the absurd"), a form of argument in which a proposition is disproved by logically following its implications to an absurd conclusion, can be a valid argument.

19. Straw Man Arguing against a misrepresentation or over-simplification of the position actually held by an opponent.

20. Special Pleading (Ad Hoc Reasoning) The arbitrary introduction of new elements into an argument in order to amend them so that they appear valid. E.g., “ESP doesn’t work in the presence of skeptics.” A subtle fallacy which is often difficult to recognize.

21. Tu Quoque To reject a position because someone (inconsistently) holds it. Also called an Appeal to Hypocrisy. Person 1: “Smoking tobacco is bad for you.” Person 2: “You smoke, therefore, your argument is invalid.” (Latin, “you too.”)

All this was taken from http://www.unifreethought.com/2011/03/avoid-logic-failz.html

Views: 988

Comment by Heather Spoonheim on March 30, 2011 at 12:43pm
Thanks, Loop Johny.  I'll keep this on hand - well, bookmarked.
Comment by Loop Johnny on March 30, 2011 at 1:46pm
If someone can take his time to give an example and/or explain each fallacy, I will be very grateful.
Comment by Bryan B on March 30, 2011 at 8:44pm
Misrespesnting and abusing language is another very common one. Like confusing faith and knowledge or calling atheism a religion
Comment by Heather Spoonheim on March 30, 2011 at 8:57pm
On that note, Bryan, I have seen people making multiple assertions about the meaning of words/phrases, constantly asking "do you agree", as though there is some intellectual merit in the ad hoc construction of a Rube Goldberg grammatical mechanism.  Is there an actual 'name' for that sort of bs, or can I just coin it as "Argument from Obfuscation" a.k.a - the Chewbacca Defense.
Comment by Bryan B on March 30, 2011 at 9:47pm
I call it the Redefinition Game, you redefine words to suit whatever it is ya want.
Comment by Lee Davis on March 31, 2011 at 11:21am
A catholic friend once tried to convince me of the accuracy of the gospels with an ad hominem argument. He stated, in essence, that the apostles were all well-regarded, respectable men in their day and that it would have been unlikely that they would have staked their reutations on the the positions they were asserting without good reason. Leaving aside all of the many arguments one could make about the existence of those men and so on, the basic premise is a classic ad hominen argument. These guys were top drawer follows, and they wouldn't lie.
Comment by Lee Davis on March 31, 2011 at 11:23am
By the way, LJ, thanks for posting this. It's excellent.
Comment by Bryan B on March 31, 2011 at 2:51pm
Thanks for the verbal fallacies Kris I have never seen those before. I had always just categorized language problems all under one category. So, thank you posting that.
Comment by Mausy5043 on April 1, 2011 at 8:14am

I find your article very interesting. I've been wanting to compile such a list for some time myself. Now you've helped me a great deal.

I'm looking for real-life examples of these (preferably non-religious) that I can use to support these in discussions I'm having or will most probably have in the future. Any suggestions?

Comment by Mausy5043 on April 1, 2011 at 8:17am
One example of number 8 or 9 (I can't make up my mind which one) is the recent "discussion" that the earthquake in Japan was caused by a solarflare. Because there was a solar flare only days before the quake, and there was also a solar flare just before the quake in ... (I don't recall of the top of my head). But that's the general idea of the argument anyway.

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