Hidden Pair
Two digits that fit in only two cells of a unit. Everything else in those cells can be discarded.
What it is
A hidden pair is the mirror image of a naked pair. Here two digits can each go in only the same two cells of a unit. Since both digits need a home and only those two cells are available, they must occupy them. Any other candidates in those two cells are therefore impossible and can be erased — which usually turns the hidden pair into a visible naked pair.
How to spot it
Count, for each digit missing from a unit, how many cells could take it. Digits appearing in exactly two cells are candidates. If two different digits point at the same two cells, you have a hidden pair. The cells themselves often carry four or five pencil marks, which is what makes the pair hidden.
Worked example
Step through the reasoning below. Each step adds one layer: first the position, then the pattern, then the candidates involved, and finally what can be eliminated.
Step 1 of 4: The starting position
- Pattern cells
- 8/3, 9/1
- Digits
- 3, 9
- Eliminations
- 8/3
Press a marked square to point it out on the board above.
Why it matters
Hidden pairs clean up cluttered cells and are frequently the only way forward when the grid is dense with candidates. They are harder to see than naked pairs precisely because the useful information is buried under extra notes.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
Why is it called hidden?
Because the two cells usually show several candidates, so nothing stands out visually. The pair only becomes apparent when you count where each digit can go.
What do I do after finding one?
Delete every other candidate from those two cells. The hidden pair then becomes a naked pair, which may allow further eliminations in the same unit.
How do I find hidden pairs faster?
Work digit by digit and note which cells could take each one. Digits with exactly two possible cells are worth comparing against each other.
Put it to use
Where you will meet it
Medium grids are where this move starts to matter: the obvious cells run out and the pattern takes over.
Play MediumStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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