The intuition
Hidden Pair is the mirror image of Naked Pair. A Naked Pair starts from two cells and notices they share the exact same two candidates. A Hidden Pair starts from two digits and notices they're both confined to the same two cells — the cells themselves might still list several other candidates on paper, but two of those digits are secretly locked in. Once you see that, the extra candidates in those two cells are noise: they can never actually be placed there, because the unit needs those two digits in exactly those two spots.
When you'll use it
Hidden Pairs live in the same territory as Naked Pairs — Medium and Hard puzzles — but are easier to miss because the cells involved often look 'busy' with several candidates. Most solvers learn Naked Pair first and only add Hidden Pair once they hit a board that a Naked Pair scan alone doesn't crack.
How to spot a Hidden Pair
- Pencil-mark every empty cell of one unit (row, column or box).
- Pick two digits, e.g. 3 and 7, and find every cell in the unit where either is still a candidate.
- If exactly two cells between them hold all the 3s and 7s in that unit — that's a Hidden Pair.
- Delete every other candidate from those two cells, leaving only {3, 7} in each.
Why the Hidden Pair logic works
The unit must contain exactly one 3 and one 7 somewhere. If the only cells that can legally hold a 3 or a 7 are the same two cells, those two cells are the designated home for 3 and 7 — no other digit can also live there, because that would leave nowhere for one of 3 or 7 to go. So any extra candidate sitting in those two cells is impossible and can be erased, even though the digits 3 and 7 themselves haven't been placed yet.
A worked Hidden Pair example
Suppose row 6 is fully pencil-marked and only R6C3 and R6C8 can still hold a 3 or a 7 anywhere in that row. R6C3 currently shows {3, 7, 9} and R6C8 shows {3, 7, 5}. Because 3 and 7 have nowhere else to go in row 6, they must occupy R6C3 and R6C8 between them — so the 9 and the 5 can be erased, leaving {3, 7} in both cells.
Walkthrough
Every other cell in row 6 has already been eliminated as a candidate for 3 and for 7 by pencil-marks worked out elsewhere on the board — only R6C3 and R6C8 remain open for either digit.
R6C3's full candidate list is {3, 7, 9}. R6C8's is {3, 7, 5}. Neither cell is a Naked Pair on its own — each has three candidates, not two — so a Naked Pair scan would walk right past this.
But look at the digits, not the cells: 3 has exactly two legal homes left in row 6 (C3 and C8), and so does 7. Between them, C3 and C8 must take the values 3 and 7 — there's no third cell for either digit to hide in.
That forces the 9 out of R6C3 and the 5 out of R6C8. Both cells collapse to exactly {3, 7}, and the next pass of the row usually turns up a Hidden Single once those digits are placed.
How to drill this technique
Take a Medium puzzle you've already pencil-marked. For each unit, instead of scanning cells for matching pairs, scan digits: for each digit 1–9, count how many cells in the unit still list it as a candidate. Any digit with a count of exactly two is a Hidden Pair candidate — check its partner.
Common mistakes
- Only scanning cells for identical candidate lists — that finds Naked Pairs, not Hidden Pairs. Hidden Pairs require scanning by digit.
- Forgetting to remove the extra candidates once the pair is confirmed — the elimination is the entire point of finding a Hidden Pair.
- Mixing up which unit the pair lives in. A Hidden Pair found in a box only eliminates within that box, not along the rows or columns that pass through it.
FAQ
What's the real difference between a Hidden Pair and a Naked Pair?
A Naked Pair is two cells whose candidate lists are both exactly the same two digits — nothing else. A Hidden Pair is two digits confined to the same two cells, even though those cells may carry several other candidates that then get eliminated. They produce a similar result (two cells locked to two digits) but you find them by scanning in opposite directions: cells-first for Naked, digits-first for Hidden.
Why is Hidden Pair harder to spot than Naked Pair?
Because the cells involved don't look like a pair at first glance — they often carry three, four or even five candidates each. The pair is 'hidden' inside a longer list, and you only see it by tracking where each digit can still legally go, not by comparing cells to each other.
Does a Hidden Pair place a digit immediately?
Rarely on its own. Like a Naked Pair, its main job is elimination — stripping the extra candidates from the two cells involved. That narrower candidate list very often exposes a Hidden Single on the next scan of the same unit.
Can a Hidden Pair happen in a 3×3 box?
Yes — a Hidden Pair can occur in any unit type: row, column, or box. Box-based Hidden Pairs are the ones beginners miss most often, because it's easy to focus scanning attention on rows and columns alone.
Is there a Hidden Triple too?
Yes. A Hidden Triple is three digits confined to the same three cells of a unit — exactly the same logic scaled up by one. It's rarer and more work to spot by hand, but shows up occasionally in Hard and Expert puzzles.
What to learn next
Once Hidden Pair feels natural, move on to Pointing Pair — it builds directly on the candidate-tracking habits you've just developed. Or revisit the full Sudoku techniques library to see the full progression from beginner to advanced.