Universal Ethics > Skills > Reasoning Fallacies

Reasoning Fallacies

Have you ever attended a presentation or debate where a speaker is presenting a claim or assertion about something? Almost certainly you have! How can you tell if their assertion is true or false? There are two basic things you would need to do:

If they presented false evidence or faulty reasoning, it is possible that their assertion might be correct anyway, by luck. However, you would be unwise to have confidence in their assertion if that is all you have to go on!

Whenever you listen to a presentation or a debate, watch for these mistakes:

Appeal to Ignorance
Claim: Something must be true because it hasn’t been proven wrong.
Examples: “I didn’t steal the cookie from the cookie jar; nobody can prove otherwise!”
“The cow jumped over the moon; nobody can prove that super cows don’t exist somewhere in the universe!”

Wishful Thinking
Claim: "If I want it to be so, it must be so; if I don’t want it to be so, it cannot be so.”
Example: “Global warming is not caused by carbon dioxide emissions. If it were, I may be required to replace my coal-fired power plant, but I don’t want to do that! It would cut into my profits!”

After this, therefore because of this
Latin: Post Hoc ergo prompter hoc
Claim: Events happened one after the other; therefore the second event was caused by the first.
Example: “I ate ice cream and then I was sick; therefore the ice cream made me sick.”

Sunk cost
Claim: We should continue a project because of all the money that was spent on it.
Example: “I said I would build this factory for $3 million. So far we have spent $4 million on it, and for another $1 million we can finish it. We can’t stop now, or all our work would be wasted!”

Begging the Question (Circular argument)
Claim: If I say it again with different words, I don’t need to explain!
Example: “There really is a Santa Claus at the North pole. How do I know? It’s because Saint Nicholas is another name for Santa Claus and Saint Nicholas lives at the North Pole; therefore Santa Claus lives there.”

Exaggeration (“Straw Man”)
Claim: If you exaggerate your opponent’s claim, you can disprove it.
Example: “My worthy opponent has said that the fines on parking tickets should be increased. This is clearly just a way to grab money from people. Don’t we already pay enough tax money to pay for roads? Now we will have to pay more! Soon everyone will be in poverty. We’ll have to go begging to get enough food to eat. Clearly such a proposition cannot be accepted!”

See a short YouTube Video about the "Straw Man" posted by Kevin deLaplante of The Critical Thinker Academy.

Diverting attention to an irrelevant argument (“Red Herring”)
Claim: If you can’t convince, confuse or distract!
Example: “Marijuana doesn’t hurt anybody! Lots of people take drugs. Just yesterday I took an aspirin for a headache. There are lots of useful drugs in the world, yet if we accept your argument people would be stopped from using some of them. For example, there is strong proof that Aspirin and Tylenol are both effective for a headache…”

See a short YouTube Video about the "Red Herring" posted by Kevin deLaplante of The Critical Thinker Academy.

Slippery Slope
Claim: If we implement the proposition, it is inevitable that worse changes will also be eventually implemented.
Example: “Children should not be allowed to eat any candy. Candy is delicious, and if a person eats some they may eat more and more. Candy is full of sugar and too much makes people fat and unhealthy. Eventually the whole population will be sick and obese.”
NOTE: “Slippery slope” is NOT a fallacy if you can prove that the worse results are likely to occur as a result of the initial decision; however, in the example no attempt is made to prove that. It is merely assumed.

See a short YouTube Video about the "Slippery Slope" posted by Kevin deLaplante of The Critical Thinker Academy.

Attacking the person rather than the proposition
Latin: Ad hominem
Claim: The person’s opinion is not correct because the person has a poor reputation.
Example: “Joe says the sky is blue but that can’t be true because Joe is stupid and nasty!”

Appeal to Authority that lacks relevant expertise
Claim: A respected authority is always correct regardless of the topic.
Example: “Wayne Gretzky eats Fruity Loops cereal, so you should too!”
NOTE: Appeal to authority is NOT a fallacy if the authority has relevant expertise (it’s a short-cut substitute for presenting facts; sometimes it’s necessary for a complex topic that can’t be explained within the time available.)

Popular Appeal (Hasty Generalization)
Latin: argumentum ad populum, and argumentum ad numerum
Claim: The popular opinion or majority is always right.
Example: “In the 1960s most adults smoked tobacco. Therefore smoking must be a healthy choice.”

Making Excuses (Special Pleading)
Claim: My proposition must be correct because I deserve special consideration that is not given to others in the same circumstances.
Example: “I don’t deserve a parking ticket just because the meter ran out. It’s not my fault. I don’t know how to tell time.”

Appeal to Flattery
Claim: You should believe me because I flatter you.
Example: “I think you’re fantastic! Your company would do well to invest in my product. Don’t you agree?”

Two Wrongs make a Right
Claim: If one person does something wrong, another is entitled to do likewise.
Example: My brother Billy stole a cookie without permission; therefore I may take one too.

Using a Pun (Equivocation)
Claim: I can trick someone to believing by misusing a word that has two meanings.
Example: “A feather is light. What is light cannot be dark. Therefore a feather cannot be dark.”


Claim: If I say it often enough, it will be believed. (Latin: Ad nauseum – until I’m sick of it!)

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