Skip to content
Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

sound

An argument is sound if it is valid and all its premises are actually true.

A sound argument is a deductive argument that is valid and whose premises are all true. The conclusion of a sound argument must be true. Logic alone can check validity; checking the premises takes knowledge of the world.

Examples

  • "All mammals breathe air. Whales are mammals. So whales breathe air." Sound.

See also

unsound valid
Read the full section →