Fallacy – a flawed general type of argument that establishes a faulty connection between premises and conclusion, thus failing to give us a good reason to accept the conclusion.

Fallacious argument – an argument whose conclusion does not follow from its premises, because its reasoning rests on a fallacy.

There are two main types of fallacies:

  1. Informal
    • the error lays in both the content of an argument and its relationship with external info
    • for example, ‘Alice says that my band is world-class – and she should know!’
  2. Formal
    • the error relates to the structure of an argument only
    • for example, ‘All world-class bands have fans. My band has fans, making it a world-class band’

Check out our article on the argument structures to understand the logic and possible errors of formal fallacies better.

Also, before reading further, we suggest you read an article about 10 common fallacies with illustrative examples and explanations.

Argument by appeal

  1. To irrelevant authority
    • invoking an authority that isn’t actually able or qualified to prove your point (the president of Italy’s choice of car doesn’t provide a definitive answer to the question of which is the best small car).
  2. To popularity
    • asserting that whatever is popular must be true or good (there is no simple or direct relationship between book sales and quality, as every author is painfully aware).
  3. To sympathy
    • invoking sympathy as a sufficient reason for agreeing with something (although we may feel sorry for someone who has had a rough time, this should have no bearing on our assessment of the quality and accuracy of their work).
  4. To force
    • using the threat of violence to compel agreement (the moment we force someone to agree with us through threats, we are abandoning the principle of reasoned debate, together with its interest in pursuing truth).
  5. To nature
    • for example: don’t get your ear pierced, it is unnatural!
  6. To tradition
    • for example: of course, you can have a husband at 12. That is a venerable tradition of our people!
  7. To ignorance
    • true unless proven false, false unless proven true
    • for example: there is no such thing as evolution. Scientists have spent centuries trying to prove its truth beyond all doubt, and they have failed again and again.

Ad hominem – a fallacy of attacking the person making an argument rather than what they actually say.

My doctor tells me to eat healthy and exercise more. What does he know? He is overweight and barely able to walk.

Fallacy of ambiguity – shifting the meaning of terms during reasoning, or exploiting uncertainty in order to support an unjustified conclusion.

You are the light of my life. But all lights must be switched off – and so, too, must you.

A Scotsman never flees from a foe in the battle. You say Alan from the Riddell clan just fled from a foe last week? Well, he is no true Scotsman!

The fallacy of composition – mistakenly arguing that whatever is true of the individual parts must also be true of the whole.

Some of this data is useful. Therefore, all of this data is useful!

The fallacy of division – mistakenly arguing that whatever is true of the whole must also be true of its individual parts.

This research is quite valid and trustworthy. Therefore, every single word of it is true.

Begging the question – putting the conclusion to be proven into your premises, thus producing something convincing-sounding that proves nothing.

The Bible is the word of God, for God says so in the Bible.

Causal fallacies

Post hoc ergo propter hoc – the fallacy of assuming that, when one thing happens after another, the first thing must be the cause of the second thing.

He quit drinking and died the next day. That must have been a shock!

Inverting cause and effect – the fallacy of confusing the direction of causation between two related phenomena, and thus mistakenly labelling an effect as a cause.

Many people buy clothes for kids and soon give birth to a baby. Probably buying clothes for kids helps people have babies!

False dilemma – fallaciously claiming that, in a complex situation, it is only possible for one of two things to be true.

Either you vote for our party, or you are against your own country.

Loaded/complex question – asking a question about one thing that also includes an unstated assumption about another, in an attempt to force someone to accept this assumption.

Will you admit that you have benefitted greatly from the atrocities committed by your government?

Faulty analogy – claiming two things are similar, even though they are not, in order to make an unreasonable conclusion look reasonable.

Faulty generalization – using a small amount of evidence to justify a much larger observation that isn’t actually warranted.

I know nobody who supports the government. The whole nation hates them!

Slippery slope – arguing on the basis that, if one small thing is allowed to happen, an inevitable and increasingly serious chain of further events will be set in motion.

First you go for a walk with that boy, then you go to the movies, and what’s happening next?!

Base rate neglect – most As are Bs. Few Cs are Bs. Someone is B. Probably, someone if an A.

Most Olympic champions are very sportive. Most non-Olympic champions are not very sportive. She is very sportive. Probably, she is an Olympic champion.

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