Logical Fallacies
John Barban has this nice list of Logical Fallacies. I should make my own too…
Logical Fallacies | JohnBarban.com
1. Ad hominem
An ad hominem argument is any that attempts to counter a claim or conclusion made by someone else by attacking the person rather than addressing the argument itself.
Example: Joe says you need to eat less calories to lose weight, but what does Joe know, he’s skinny and never lost weight before.
2. Ad ignorantiam
This is also called the argument from ignorance and the basic premise is that a specific belief is true because we don’t know that it isn’t true.
Example I could argue that small undetectable pollutants floating around in the air are causing obesity, but we can’t prove it.
3. Argument from authority
Stating that a claim is true because a person or group of perceived authority says it is true. Although it is reasonable to give more credence to the claims of those with the proper background, education, and credentials.
Example: Stating something is true because “my doctor says so”.
This doesn’t mean they are always correct and furthermore it doesn’t mean they have any authority to make claims outside of their specific area of expertise.
The truth of a claim should always come back to logic and evidence and not merely the supposed authority of the person promoting it. Credentials and expertise are an indication of the tools needed for a person to be qualified to gather the needed evidence in a given area to make a truly informed claim. For example, I might think I know whats wrong with my car when there is a rattle coming from under the hood, but my mechanic has the credentials and expertise to investigate the rattle and determine what it is for certain. He may not know the answer just by hearing my story about the rattle at first, but he can employ is expertise and education to discover what it is.
4. Argument from Personal Incredulity
I cannot explain or understand this, therefore it cannot be true. It is not a valid argument to assume something is not true simply because you personally don’t understand it.
Example: Not believing that antibiotics can help get rid of an infection simply because you don’t understand how an antibiotic works in your system, and therefore because you don’t understand how an antibiotic works it must not be possible and not work at all.
5. Confusing association with causation
This is the assumption that because two events are correlated that one must have caused the other.
Example: Many women who are fit and go to the gym regularly wear lululemon pants, therefore lululemon pants make you fit and go to the gym.
6. Confusing currently unexplained with unexplainable
Assuming that any phenomenon that is currently unexplained is by nature unexplainable. This is a very limited way of thinking. Science is always uncovering new insight and information and most unexplained phenomenon will eventually be explained with enough investigation.
Example: We currently cannot explain with 100% certainty why some people gain weight easier than others, and therefore we will never know.
As with any scientific field of research we are always investigating and finding more information. Just because we don’t have the full answer today does not mean we will not find the answer tomorrow.
7. False Continuum
The idea that because there is no obvious and definitive difference between two extremes that there is no difference between them at all.
Example: Claiming that all carbohydrates are ‘bad’ for you and assuming that white refined sugar can be classified the same as the ’sugar’ you get from a fruit or vegetable.
8. False Dichotomy
Erroneously and arbitrarily reducing many possibilities down to only two.
Example: if high sugar foods can contribute to health problems we must never eat sugar at all.
It is clearly possible to avoid health problems and still eat some amount of sugar.
9. 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.
Example: Eating too much fat is bad for you and therefore any foods that contain fat are not meant to be consumed by humans.
10. 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.
Example: You had pizza for dinner last night and woke up with a headache today, therefore the pizza must have caused the headache.
11. 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.
Example: If carbohydrates are bad for us (as the low carb people would say) then that means all fruits and vegetables must also be bad for us and therefore we should never eat any of them.
12. 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.
Example: Eating less sugar cannot be the correct answer for weight loss because that would mean we would have to change the fundamental way we process food, shop for food, subsidies crops, cook all baked goods, and could never eat at a restaurant ever again.
13. Special pleading, or ad-hoc reasoning
This is a subtle fallacy which is often difficult to recognize (and one of my biggest pet peeves). 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.
Example: You may claim that you can lift more weight than me, and we test your claim and determine that you in fact cannot life more weight than mean. At this point you begin with a series of excuses why on the particular day of the test you weren’t wearing the right shoes, and the weights weren’t calibrated correctly, and it wasn’t the correct humidity in the room etc…these are all arguments from special pleading in order for you to maintain your claim that you are still in fact stronger than me even though we have completed a test which proved otherwise
14. Straw Man
Arguing against a position or claim which you create specifically to be easy to argue against, rather than arguing against the real position and claim held by those who oppose your point.
Example: I may state that weight training will make your muscles stronger, and you may argue back that everyone who goes to a gym won’t get stronger. In this case you would have replaced my statement about ‘weight training’ with ‘everyone who goes to a gym’. Clearly people go to the gym for all different kinds or workouts, and many of them do not do weight training at all.
15. 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. It may not be immediately apparent when this fallacy is being used because of the way the argument is stated.
Example: Eating too much sugar makes you fat, therefore if you’re fat you must have eaten too much sugar.
16. The Moving Goalpost
A method of denial arbitrarily moving the criteria for “proof” or acceptance out of range of whatever evidence currently exists.
Example: You say that a study of 100 people showed that exercises 3 times per week for 1 hour did not help people lose weight, and then I say “there weren’t enough people in the study, if they studied 1 million people it would show a different result”
It is easy to move the goal posts on any argument to make a claim seem false or to maintain support for a false claim.
17. 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.”
Example: Someone sells you a placebo sugar pill and tells you it can help with weight loss, and when challenged on this practice they point out that other pills don’t do anything either.
18. Unstated Major Premise
This fallacy occurs when one makes an argument which assumes a premise which is not explicitly stated.
Example: Stating that we should label food that is low in fat because many americans are overweight. The unstated major premise is that 1) Simply labeling foods as low fat foods can help reduce the rate of overweight americans 2) That being overweight is unhealthy 3) That eating high fat foods themselves are a contributing cause to overweight.
