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Knights and Knaves — rules and where to play

KNIGHTS AND KNAVES · Truth-tellers and liars / Logic island

On the island everyone tells only truth or only lies; you infer who is who from what they say. Raymond Smullyan turned it into an art.

Origin
1978 · United States
Difficulty
★★★★★ 3–5 / 5
Time
10–40 min
Grid
—
Sites
2

Rules

  1. Two kinds: knights always tell truth, knaves always lie (sometimes a "random" is added).
  2. Each statement's truth must match the speaker's kind.
  3. Self- and cross-references let you pin every identity.

How to start

Find the self-referential line first

"I am a knave" is self-contradictory and fixes the speaker at once.

Test by assumption

Assume A is a knight; if their statement breaks, they are a knave.

Use "he says he is X"

Identity claims combined with the truth rule often settle it.

Where players get stuck

  • Forgetting a liar's whole statement is false, taking half of it as true.
  • Skipping a truth table and intuiting a chain of wrong calls.

Play Knights and Knaves

2 sites
BrainBashersFree

Been free for years. A daily logic set, plus Sudoku variants, Kakuro and Nonograms.

Open → Erich's Puzzle PalaceFree

Erich Friedman's long collection — 130-plus types, all over the map.

Open →

Browse All-in-one portals →

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About this page
  • Last updated 2026-09-22
  • Source Curated compilation of established puzzle rules and listed third-party play sites
  • Audience Players learning Knights and Knaves rules or looking for online sites to play
  • Covers Rules summary, how to start, common pitfalls, and the dedicated play sites listed on this page
  • Does not cover Hosted puzzles, worked solutions, official contest rankings, third-party uptime or pricing guarantees
  • Not advice This page is puzzle reference content only. It does not constitute financial, legal, medical or other professional advice.
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