A deduction puzzle gives you a set of suspects, a set of places and a set of
objects, plus a list of clues. Exactly one combination satisfies every clue.
The grid is the tool for finding it.
Published 11 May 2026 · Updated 13 August 2026
The method
Mark what cannot be true first. Negative clues
("the doctor was not in the library") are usually more useful than positive
ones, because each one removes a possibility permanently.
Use the grid, not your memory. Every cross you place is a
fact you never have to re-derive.
Look for forced cells. When a row or column has one square
left uncrossed, that square is true — and it lets you cross out the rest of
its row and column.
Chain inferences. If the chemist was in the conservatory,
and the conservatory held the candlestick, then the chemist held the
candlestick — even though no clue said so.
Re-read the clues after every breakthrough. A clue that told
you nothing on the first pass often becomes decisive once two other facts
are settled.
Common mistakes
Assuming a clue implies more than it says; forgetting to propagate a deduction
across all three grids; and accusing before the board is complete. In Deduce a
wrongful arrest ends your streak, so it pays to finish the grid.