Three inhabitants, three different natures and a single possible assignment. Here, unlike other island puzzles, there is a type of inhabitant whose behavior does not follow any fixed pattern — and that changes everything.
The knight, the squire and the spy
Riddle statement
On an island there are three types of inhabitants:
- gentlemen, who always tell the truth;
- squires, who always lie;
- spies, who can tell the truth or lies.
You meet three people: A, B and C.
- A says: “B is a gentleman.”
- B says: “A is a gentleman.”
- C says: “A is a squire.”
Knowing that there is exactly one knight, a squire and a spy, who is who?
Show solution
Solution
Answer:
- A is the squire.
- B is the spy.
- C is the knight.
We analyze starting from C.
C says: "A is a knave." If C is a knight, that sentence is true, so A is a knave. Since we already have a knight and a squire, B is left as a spy.
We check the three sentences with this assignment:
- A says: "B is a knight." It is false, and A is knave: it fits.
- B says: "A is a gentleman." It's false, but B is a spy and can lie: it fits.
- C says: "A is a knave." It is true, and C is a knight: it fits.
We now rule out the other possibilities for A.
A cannot be a knight: his sentence "B is a knight" would be true, which would give two knights. Contradiction.
A cannot be a spy either. If A were a spy, B and C would be knight and knave in some order. B says "A is a knight," which would be false, so B cannot be a knight; I would be a squire. Then C would be a knight, and his sentence "A is a knave" would have to be true, but A would be a spy. Contradiction.
A can only be a squire. From this it follows that C is a knight and B is a spy. The assignment is unique: A = squire, B = spy, C = knight.