A liar puzzle is a logic puzzle where some people always tell the truth and some always lie. You can't believe what anyone says, but you can reason about it. Hearsay is a free daily one, with a new case every day.
What is a knights and knaves puzzle?
Knights and knaves is the classic form. Knights always tell the truth. Knaves always lie. You meet a few of them, each makes a statement, and you work out who is who.
Hearsay uses the same idea with different names. People are honest or liars, and the puzzle gives you a whole grid of them at once.
How do you solve one?
Pick a person and try each possibility. Follow what it forces, and drop any choice that leads to a contradiction. Here's a small example.
- Suppose A is honest. Then B is a liar. B's statement says A and B are the same kind, which is false. A liar's statement is false, so that fits. This works.
- Suppose A is a liar. Then "B is a liar" is false, so B is honest. B's statement says A and B are the same kind, but A is a liar and B is honest. That's false, and an honest person can't say something false. This breaks.
So A is honest and B is a liar. One of the two options fell apart, and that's how you know.
What's the trick with lies?
A lie is only useful if you flip it. If a liar says "I have exactly 2 honest neighbors", then it's true that they don't have exactly 2. A lie tells you something definite, just in reverse. In Hearsay, when you mark someone a liar, the game writes out the true version for you under a "Truth" line.
There's one more trick worth knowing. If a person says something about themself and one other person, you can often settle the other person whether the speaker is lying or not. "Exactly one of Cleo and me is a liar" always means Cleo is a liar. Try it both ways: an honest speaker makes it true, so Cleo is the liar; a lying speaker makes it false, so the two of them are the same, and the speaker is a liar, which makes Cleo one too.
How does Hearsay turn this into a daily puzzle?
Hearsay puts a grid of people on screen. Each one has a name, a job and a single statement. The statements are about the grid: how many liars are in a row, who sits next to whom, whether two people are the same kind. One person is revealed to start, and a daily rule, like "Every column has exactly one liar", is always true.
- Every clue is visible from the start, so you choose where to begin.
- There is always a mark you can prove from the rule and at most two clues, so you never have to guess.
- The board grows from 9 people on Monday to 15 at the weekend, and the rules get harder to use.
- A lightbulb gives you a hint if you're stuck, and the game counts it.
Read how to play Hearsay, or follow a whole case, step by step.
Are there other puzzles like this?
If you enjoy Hearsay, you may like Clues by Sam, a daily puzzle where you sort a grid of suspects into innocent and criminal, or the detective logic of Murdle. For other kinds of reasoning, try Enigma, our code-breaking game, or browse all logic puzzles.
Hearsay isn't affiliated with any puzzle book or game that uses the knights and knaves idea.