Find-the-liar puzzles, with three to try
A find-the-liar puzzle gives you a few people, each with a statement, and tells you that one of them is lying. Your job is to work out who. You don’t need a hunch: suppose each person is the liar in turn, and look for the one choice where every other statement can be true at the same time. Below are three free mini puzzles in the style of Lie of Sight, a daily find-the-liar game, each with its answer hidden until you want it.
What counts as a find-the-liar puzzle
They go by a few names, but they share one shape: some people make statements, some of the statements are false, and you’re told enough about the liars to pin them down.
- Who-is-lying riddles. Four friends, one broken window and four statements, only one of them false. These usually come with exactly one liar, and the statements point at each other.
- Liar and truth-teller puzzles. Each person always lies or always tells the truth, and you work out which is which. The classic version is knights and knaves, where any number of people can be lying.
- Picture puzzles. In Lie of Sight, each statement is about what someone could see in a room. Exactly one person is lying, and you prove it by moving people around the board. Each of the family sees by one rule, set out in Meet the Fibbersons.
What they don’t need is a hunch. The statements are the whole puzzle, and a good one has exactly one answer.
How to solve one
There’s one method that always works, and a shortcut that usually gets you there first.
- Pick the fussiest statement.Start with the one that pins someone down the most: a statement that can only be true in a few places, or one about two people at once.
- Suppose that person is the liar.Then everyone else is telling the truth, so treat their statements as facts.
- Look for a clash.If two of those facts can’t both hold, your guess was wrong. Cross that person off and try the next.
- Check the survivor.The liar is the one guess with no clash. Make sure every other statement can be true at the same time, and you’ve proved it.
The shortcut: if believing someone means two other people must be lying, that someone is the liar, because only one person lies. Most puzzles with one liar fall to this.
Want to see it on a real board? Follow every step in how to solve a find-the-liar puzzle: a worked example.
Three mini puzzles to try
Each one is a small room seen from above, in Lie of Sight’s style. The rules you need:
- Dad sees his whole row and column.
- The Kid sees his row and column too, but he’s short, so low things like the vase block him as well.
- Grandma sees two squares in all eight directions.
- Walls and tall things (the bookshelf, the clock) block everyone’s view. People never do, and nobody stands on a prop.
- Exactly one person is lying. Anyone not drawn could be standing on any empty square.
You’re not finding who did it, just who’s lying about what they saw.
Mini puzzle 1: the vase (easy)
Someone filled the vase with jelly beans.
Dad “I saw the Kid.”
Grandma “I saw the vase.”
The Kid “I saw the vase.”
Where could the Kid be standing so that every story but one is true?
Show the answer
Grandma is lying.
Grandma is already standing, so check her first. She sees two squares in each of eight directions, and the vase is exactly two squares away, up and to her right. But the tall bookshelf stands on the square between them, and tall things block her view.
So Grandma’s story can’t be true, wherever anyone else stands. A story that fits nowhere belongs to the liar.
The other two fit together: put the Kid in the top-left corner. He sees along the top row to the vase, and Dad sees him straight up his column.
Mini puzzle 2: the ball (medium)
Someone bounced the ball off the ceiling.
Dad “I saw the ball.”
The Kid “I saw Dad.”
Grandma “I saw Dad.”
Where could Dad and the Kid be standing so that every story but one is true?
Show the answer
Dad is lying.
Start with Dad’s story, because it pins him down most. The ball is tucked into the top-left corner: a wall runs under it and the square beside it, and the bookshelf blocks the top row. So the only square Dad could see the ball from is the one right next to it.
Now look at that square. Grandma can’t see it: it’s three squares away and the bookshelf is in the way. The Kid can’t see it from anywhere either: the wall closes it off from below, and the bookshelf closes the row.
So if Dad were telling the truth, Grandma and the Kid would both be lying. Only one person lies, so it’s Dad. One way it works: Dad two squares below Grandma, and the Kid at the bottom of the same column. They both see him.
Mini puzzle 3: the clock (harder)
Someone stopped the clock at teatime.
Dad “I saw the clock. I didn’t see the Kid.”
The Kid “I saw Dad.”
Grandma “I saw the vase. I saw Dad.”
Where could Dad, the Kid and Grandma be standing so that every story but one is true?
Show the answer
Dad is lying.
Start with Dad and the Kid. They both see along their row and column, and anything that blocks Dad (walls and tall things) blocks the Kid too. So if the Kid saw Dad, Dad saw the Kid. The Kid’s story and Dad’s “I didn’t see the Kid” can’t both be true: one of them is the liar, and Grandma is honest.
Which one? Suppose Dad is honest. The bookshelf blocks the clock’s column, so to see the clock he’d have to stand in the top row. But Grandma has to be within two squares of the vase at the bottom, and from there the wall stops her seeing anyone in the top row. Dad honest would make Grandma a liar too: two liars. So Dad is lying.
One way it works: Dad in the middle, Grandma just below him beside the vase, and the Kid at the end of Dad’s row. The Kid sees Dad, so Dad saw the Kid, and his story is false.
Ready for a bigger one?
Lie of Sight has a new case like these every day: four of the Fibbersons in a furnished room, one of them fibbing. You drag them around the board, and each story turns green when it fits where they stand. When every story but one fits, you’ve found the liar. It’s free in the browser, with no sign-up, and today’s case is one tap away at the end of this page.
More on liar puzzles
- How to solve a find-the-liar puzzle: a worked example: every step on a small board, with pictures.
- Knights and knaves puzzles with answers: the classic truth-teller and liar puzzles, six to solve.
- Meet the Fibbersons and how each one sees: the family in Lie of Sight, and the one rule each of them sees by.
- How to play Lie of Sight: every rule, what blocks whom, hints and the daily.
Questions people ask
What is a find-the-liar puzzle?
A logic puzzle where several people each make a statement and you’re told how many of them are lying, usually exactly one. You work out who it is from the statements alone, with no guessing.
What’s the fastest way to find the liar?
Suppose each person is the liar in turn, and treat everyone else’s statement as true. If that leads to a contradiction, they weren’t the liar. Start with the statement that pins someone down the most.
Is there always exactly one liar?
In Lie of Sight, yes, and in the three puzzles on this page. Other puzzles set their own rules: in knights and knaves puzzles any number of people can be lying, so read the setup first.
Where can I play more find-the-liar puzzles?
Lie of Sight has a new find-the-liar case every day, free in the browser with no sign-up, and practice, 15 Case Files and 10 Tricky Cases to play any time.
Ready for today’s case?
A new case every day. Free, with no sign-up to start.