How to Solve Logic Grid Puzzles: A Step-by-Step Guide

Logic grid puzzles look intimidating, but a few habits make almost any grid fall. Here's the method Inspector Quill uses in The Lighthouse Ledger.

1. Understand the rule

Each person matches exactly one item in each category, and no two people share one. That single rule does most of the work.

2. Mark impossibilities first

Put an X wherever a clue rules out a pairing. 'Agnes was not at the boathouse' is one X. Negative clues are usually the easiest to apply.

3. When you place an O, clear its row and column

A certainty (O) means every other square in that row and column of the same block becomes X. Do this immediately; it often triggers a chain.

4. Carry facts between blocks

If whoever had the oar was at the boathouse, and Agnes had the oar, then Agnes was at the boathouse. Experienced solvers constantly check whether a fact in one block settles a square in another.

5. Treat 'or' clues as half a fact

'Barnaby had the rope or the kettle' means Barnaby had none of the other items. Strike them all.

6. Ordered clues

For times or positions, list the possible orders. 'Exactly two bells before' rarely leaves more than two or three options; test each one.

7. 'Exactly one is true'

Assume the first statement is true and follow the consequences. If the grid breaks, the second statement is the true one.

Practise with three free cases: download the sampler.