The History of Why

Concept

5 readings

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Deductive validity

Concept · 5 readings

An argument is deductively valid when its premises could not all be true while its conclusion is false. Whether the premises are in fact true is a separate question.

All readings

5 readings · Title A–Z

  • Reference article

    Argument: reasons and what they support

    An argument gives reasons for a conclusion; an explanation says why something is so. This article sets out that vocabulary and what validity does, and does not, tell us about truth.

  • Inference under challenge · Lesson 2 of 2

    Dharmakīrti: a reason that establishes its conclusion

    For Dharmakīrti, a reason must belong to its subject and be inseparable from what it establishes, and the connection must be known. The lesson compares his account with Nyāya’s, keeping apart what follows, what is known and what a countercase defeats.

  • Guided course · Module 11 · Lesson 62

    Logic, meaning and a new ideal of clarity

    Frege distinguishes an expression’s sense from its reference to explain how an identity can be informative. The lesson also shows why substituting one name for another can change what a belief report says.

  • A counterexample workshop · Lesson 1 of 1

    Testing a claim with a counterexample

    A counterexample can test a general claim, or test an inference by describing a case in which its premises are true and its conclusion false. The workshop practices both, then asks what a fair repair of an argument should preserve.

  • Guided course · Module 1 · Lesson 2

    What does a reason actually support?

    Whether a conclusion follows is one question, and whether the premises are true is another; imagining true premises with a false conclusion tests whether it follows. Reasons can still support a conclusion they do not guarantee.

Study this in sequence

  • A counterexample workshop

    Test how far a claim reaches by finding a case in which it fails, and practice on general statements, inferences and fair repairs to an argument.

  • Inference under challenge

    What makes a sign a reason to believe something we cannot see? Follow selected Nyāya accounts and Dharmakīrti’s argument to examine the connection a sign needs, our grounds for relying on it and what a countercase can show.