Mental Models: Fallacies

This is a series of tweets that I originally shared on twitter. It gained a lot more attention than I was expecting, so I decided to cross-post to my site for ease of reference.

Fallacies based on illogical reasoning or unsound arguments are common. Spotting fallacies is a priceless skill.

Here is a list of my top 15 fallacies (in no particular order) to help us all avoid common errors in reasoning.

1. SUNK COST FALLACY

Actions occurring in the past that should play no part in future decision making.

It results with chasing what you’re better off losing.

2. GOLDEN MEAN FALLACY

Concluding that the truth is a compromise between two opposing views.

Person A is convinced that the sky is blue. Person B is equally as convinced that the sky is yellow. They agree to meet somewhere in the middle, concluding that the sky is green.

3. CONFIRMATION BIAS

Unquestionably accepting information that confirms or reinforces existing beliefs.

E.g. you believe that ALL scientists are smart. So when you meet a smart scientist, it’s more "evidence" to support your existing belief. Non-smart scientists are discounted.

4. COMMON BELIEF FALLACY

Incorrectly reaching a conclusion that an argument must be true because it's a widely held belief.

You need to be able to weigh up arguments and think rationally for yourself, without others' influences or biases.

5. AD HOMINEM

Attacking your opponent’s character, personal traits, motive or authority without addressing the substance of their argument.

Think Donald Trump.

6. STRAWMAN FALLACY

Misrepresenting an opponents argument, making it easier to attack, to fit your agenda. It’s dishonest.

Again, think Donald Trump.

7. FAULTY GENERALISATION FALLACY

(AKA: Jumping to conclusions)

Drawing an expansive conclusion based on inadequate or insufficient evidence.

E.g. you've only ever seen red Ferrari's, so you incorrectly assume that all Ferrari's are red.

8. CAUSE/ EFFECT FALLACY

An illogical reasoning that because two things typically occur together, one is assumed to cause the other.

E.g. sales were down in May. A new employee joined in May. Therefore new employees cause sales to fall.

Correlation does not imply causation.

9. SLOTHFUL INDUCTION FALLACY

Arguing unfavourable outcomes as “coincidence”, despite all the facts presented.

E.g. attributing coincidence to the reason your investments have significantly underperformed the market for the last 20 years.

10. REDUCTION FALLACY

Oversimplifying a situation and asserting that there is a single cause of an outcome, when in reality, there are many causes or reasons.

E.g. An iceberg sunk the Titanic. Therefore icebergs are the only cause of all shipwrecks.

11. THE GAMBLER’S FALLACY

Incorrectly believing that the probability for an outcome after a series of outcomes isn’t the same as the probability for a single outcome.

“The last 26 spins have landed on red, so the likelihood of the next spin landing on red is less than 50%”.

12. APPEAL TO AUTHORITY FALLACY

The opinion of an authority (particularly an irrelevant one) on a topic is used as evidence to support an argument.

E.g. using the opinion of a divorce lawyer to prove a point on criminal law.

13. PERSONAL INCREDULITY FALLACY

Asserting that a proposition is false because it’s difficult to understand or it contradicts your personal expectations or beliefs.

“I can’t make a living as a YouTuber, therefore you can’t too.”

14. APPEAL TO IGNORANCE FALLACY

Claiming something to be false, because it’s yet to be proven true (and vice versa).

“No studies demonstrate that parachutes are necessary to avoid death when jumping out of planes, so we can't say parachutes are helpful.”

15. CONJUNCTION FALLACY

Assuming that the conjunction of two events is more probable than one of the events on its own.

E.g. incorrectly believing that “Linda is a teacher that loves children” is more probable than “Linda is a teacher”.

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