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Concept clusters

Related ideas that live chapters apart, pulled onto one page — every way to show an argument invalid, every rule that handles a conditional, and more.

Every way to show an argument is invalid

One idea, four tools. Find a case where the premises are true and the conclusion is false.

16 concepts →

Every way to show two sentences are equivalent (or not)

A table for a yes/no verdict, a chain of laws for a step-by-step case, a normal form for a standard shape.

13 concepts →

The fallacy families

Formal fallacies break the pattern. Informal ones break relevance, presumption, cause, or meaning.

35 concepts →

How to prove each kind of sentence

Read the goal's main connective, and it tells you which rule finishes the proof.

12 concepts →