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Logic & Arguments: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
Premises & Conclusions
An argument gives reasons, called premises, to support a conclusion. A good argument needs true premises that really do support its conclusion.
Key fact
“Therefore” often signals a conclusion.
Deduction & Induction
Deduction reasons from general rules to certain conclusions. Induction generalises from examples: every swan I’ve seen is white, so all swans are white. Induction can be wrong.
Key fact
Black swans in Australia broke that famous generalisation.
Occam’s Razor
Occam’s razor says that when two explanations fit the facts, prefer the simpler one: the one that needs fewer assumptions.
Key fact
It’s named after the 14th-century friar William of Ockham.
Burden of Proof
Whoever makes a claim usually has to back it up. “Prove it isn’t true” shifts the burden unfairly.
Key fact
Extraordinary claims need extraordinary evidence, as Carl Sagan put it.
Slippery Slopes & False Choices
A slippery slope claims one step will inevitably lead to disaster, without showing why. A false dilemma pretends there are only two options when there are more.
Key fact
“You’re either with us or against us” is a classic false dilemma.
Appeals to Authority
Citing an expert in their own field can be good evidence. But a famous person’s opinion outside their expertise doesn’t make a claim true.
Key fact
Check whether the authority is an expert on that exact topic.
Steelmanning
Steelmanning means restating the other side’s view in its strongest form before you reply. It’s the opposite of a straw man, and it makes debates fairer.
Key fact
If you can’t explain a view you reject, you may not understand it yet.
Fun facts
An argument can be valid yet wrong: “All cats can fly; Soda is a cat; so Soda can fly” follows perfectly from a false premise.
Sherlock Holmes’s famous “deductions” are mostly inferences from clues, closer to induction than strict deduction.
Ockham never wrote the phrase usually quoted, and the name “razor” came centuries after him.
Bertrand Russell’s teapot: nobody can disprove a tiny teapot orbiting the Sun, but that’s no reason to believe in it.
The “nirvana fallacy” rejects a good solution just because it isn’t perfect, a close cousin of the false dilemma.
In the 1940s, adverts used doctors to sell cigarettes, with slogans like “More doctors smoke Camels”.
Formal debate goes back at least to ancient Greece and India.
Story: The Black Swan
The Black Swan
For centuries in Europe, “a black swan” meant something impossible. The Roman poet Juvenal used it for a thing too rare to exist.
Then, in 1697, Dutch explorer Willem de Vlamingh sails up a river in western Australia, and sees black swans everywhere.
Thousands of white swans had never proved that all swans are white. One black swan was enough to prove they’re not.
True or false?
Tap your answer to see if you got it, and why.
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Question 1 of 10
Premises are the reasons given for a conclusion.
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True. They do the supporting.
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Question 2 of 10
Induction generalises from examples.
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True. From the cases we’ve seen.
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Question 3 of 10
Occam’s razor favours simpler explanations.
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True. Fewer assumptions, all else equal.
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Question 4 of 10
The person making a claim usually has to support it.
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True. That’s the burden of proof.
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Question 5 of 10
A false dilemma ignores other options.
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True. It squeezes everything into two choices.
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Question 6 of 10
An expert’s view is strongest within their own field.
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True. Expertise doesn’t transfer automatically.
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Question 7 of 10
Steelmanning presents the opposing view at its strongest.
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True. Then you respond to that.
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Question 8 of 10
An argument has no conclusion.
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False. The conclusion is what it’s arguing for.
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Question 9 of 10
Induction always gives certain conclusions.
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False. New evidence can overturn them.
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Question 10 of 10
Occam’s razor says the most complicated theory is best.
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False. It favours the simplest that fits.
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KnowSoda learns what you know and brings back what you’re about to forget. Logic & Arguments has 6 more ideas at the Advanced and Expert levels.
Sources
- Stanford Encyclopedia of Philosophy — Informal logic, the problem of induction
- Internet Encyclopedia of Philosophy — Fallacies
- Encyclopaedia Britannica — Occam’s razor, William of Ockham
- Carl Sagan (1980), Cosmos (“extraordinary claims require extraordinary evidence”)
- Stanford Encyclopedia of Philosophy — abduction, Karl Popper, Bayes’ theorem
- Internet Encyclopedia of Philosophy — fallacies
