Why Some Logic Puzzles Seem to Have More Than One Answer
Short answer: usually one early mark is wrong, or one clue hasn't been fully used. Sometimes, though, the puzzle itself is broken: its clues allow two arrangements, and the app only accepts one. A well-made puzzle is checked so that exactly one answer fits.
Reason 1: a wrong mark early on
One mistaken ✓ quietly spreads ✗ marks across its row and column, and later deductions build on it. When two options seem left, go back and check each ✓ against the clue that produced it.
Reason 2: a clue you used only once
Either-or clues and comparison clues ("older than") keep giving information as the grid fills in. If you are stuck between two options, reread these first; one of them usually breaks the tie.
Reason 3: a missed cross-category link
If A goes with B, everything you know about A applies to B in other blocks too. Copying these facts often removes the last ambiguity.
Reason 4: the puzzle really has two answers
Hand-written or hastily generated puzzles sometimes have clues that don't pin down one arrangement. Players then see an app reject an answer that fits every clue, or feel forced to guess. The fix is on the puzzle maker's side: run a solver and add clues until only one arrangement remains, and make sure that arrangement can be reached by logic alone.
How to check your grid
- Pick one ✓ and find the clue or elimination that gave it.
- Do the same for every ✓; stop at the first one you can't justify.
- Clear marks after that point and continue from there.
How Inferlo helps
Every Inferlo puzzle is checked by a built-in solver before you see it: it has exactly one answer, reachable by logic, with no contradictory clues. If you get stuck, a free hint first looks for a wrong mark and clears it, then reveals one correct pair.
FAQ
Can a logic grid puzzle really have two answers?
A badly made one can. If the clues don't rule out every alternative, two arrangements fit. Good puzzles are checked with a solver so that exactly one arrangement fits.
How do I know if I made a mistake or the puzzle is broken?
Check every ✓ against the clues one by one. In most cases a single wrong mark early on is the cause. If every mark follows from a clue and two options still remain, the puzzle is underdetermined.
Why does my app say my answer is wrong when it fits the clues?
If two answers fit the clues, an app that compares against one stored answer will reject the other one. That is a flaw in the puzzle, not in your logic.
Related guides
Play logic grids with exactly one answer — Inferlo (Google Play)