Sudoku Pairs Guide: Naked, Hidden & Pointing Techniques
By Michel ·
When scanning and singles no longer reveal a move, compare the remaining candidates. This guide introduces three pair patterns you can check when their conditions appear.
Pairs are useful patterns to check when scanning no longer produces a move. Learning naked pairs, hidden pairs, and pointing pairs gives you three different ways to remove candidates. This guide explains their conditions and suggests an order to practise them; no technique is guaranteed by a difficulty label.
Why "Pairs" — and Why Three Types?
Naked and hidden pairs concern two digits and two cells in a unit (a row, column or box). A pointing pair concerns one digit restricted to two cells in a box, both on the same row or column. These patterns have different conditions and remove candidates from different places.
Think of them as a progression system:
- Pointing pairs — one digit confined to two cells in a box, aligned on a row or column. Eliminates that digit outside the box along that line.
- Naked pairs — two cells with only two identical candidates. Eliminates from the rest of the unit.
- Hidden pairs — two candidates hiding in two cells. Eliminates the non-pair candidates from those cells.
Technique 1: Pointing Pairs
Pointing pairs are one form of locked candidates. They are useful to look for when singles stop producing progress. A difficulty label does not guarantee a particular technique.
The concept: Look inside a 3×3 box. Find a digit whose only candidate cells in that box lie on one row or column: two cells form a pointing pair, and three form a pointing triple. Because that digit must go into one of those cells, you can eliminate it from the rest of that row or column — the part outside the box.
Worked example: In a 3×3 box, the digit 4 can only go in two cells, both in row 5. Row 5 passes through two other boxes. In both of those boxes, row 5 cells that contain 4 as a candidate can have it removed — because if 4 must go somewhere in the first box's row-5 cells, it cannot also appear in row 5 elsewhere.
How to spot them: After scanning each digit globally, zoom into each 3×3 box. Ask: "In this box, which digits appear in only one row or column?" Those are your pointing pair candidates.
Technique 2: Naked Pairs
A naked pair is two cells within the same unit that each contain exactly the same two candidates — no others. Because those two digits must fill those two cells (in some order), no other cell in that unit can contain either digit.
Worked example: In a column, two cells both contain only the candidates {3, 8}. The digit 3 must go into one of them, and 8 into the other. Therefore, every other cell in that column can have 3 and 8 safely removed from their candidates. Sometimes that elimination produces a naked single elsewhere, cascading into more placements.
How to spot them: Scan each unit for cells that contain exactly two candidates. If you find two cells in the same unit with the same two-candidate set, you have a naked pair. Eliminate both digits from all other cells in that unit.
Naked triples follow the same logic: three cells in a unit that together contain exactly three candidates (distributed across the three cells, not necessarily all three in each cell). Eliminate those three digits from all other cells in the unit. Naked triples are harder to spot but worth knowing once pairs feel natural.
Technique 3: Hidden Pairs
Hidden pairs are the trickiest of the three — not because the logic is harder, but because the pair is camouflaged. A hidden pair occurs when two candidates appear in exactly two cells within a unit, and those candidates do not appear anywhere else in that unit. Unlike naked pairs, the pair cells also contain other candidates, which hides the pair in plain sight.
The key insight: If two digits can only go in two specific cells within a unit, those two cells are locked for those two digits — regardless of what other candidates are also in those cells. Once you identify the hidden pair, remove all non-pair candidates from those two cells. The cells now display a naked pair. In this unit, the pair digits were already absent from every other cell, so there is no additional elimination of those digits there.
Worked example: In a row, digits 6 and 9 appear as candidates in exactly two cells: Cell A has {2, 4, 6, 9} and Cell B has {1, 6, 7, 9}. Because 6 and 9 cannot go anywhere else in this row, they are locked to Cells A and B. Remove 2, 4 from Cell A and 1, 7 from Cell B. You are left with {6, 9} in both cells — a naked pair. In this example, 6 and 9 were already absent from the other cells; the new eliminations are the extra candidates removed from Cell A and Cell B.
How to spot them: Shift your focus from cells to digits. For each digit in a unit, note which cells it can go into. When two different digits share the same two cells — and only those two — you have a hidden pair.
Using All Three Together
One approach is to check each box for pointing pairs, then each unit for naked pairs, then hidden pairs. After an elimination, look for newly revealed singles. Use any deduction whose conditions you can prove.
A suggested practice order is:
- Naked and hidden singles (basics)
- Pointing pairs / locked candidates
- Naked pairs (and triples)
- Hidden pairs (and triples)
- More advanced techniques if still stuck
Once you are comfortable with pairs, the natural next step is X-Wing and Swordfish for row/column patterns, and for an advanced pairs extension, explore the Sue de Coq technique — which builds directly on the locked candidates logic of pointing pairs.
Frequently Asked Questions
What is a naked pair in Sudoku?
A naked pair is two cells in the same unit that each contain exactly the same two candidates — and only those two. Because those two digits must occupy those two cells, you can safely remove them from every other cell in the same unit.
What is a hidden pair in Sudoku?
A hidden pair occurs when two candidates appear in exactly two cells within a unit, and those candidates don't appear anywhere else in that unit. Even though the pair cells contain other candidates too, those two digits are locked there — so you can remove all other candidates from the pair cells.
What are pointing pairs in Sudoku?
A pointing pair is a form of locked candidates: a digit has exactly two candidate cells in a 3×3 box, and both lie on the same row or column. Because that digit must go in one of those cells, you can eliminate it from the rest of that row or column outside the box.
In what order should I learn these three pair techniques?
Try pointing pairs first, then naked pairs, then hidden pairs. This is a suggested learning order, not a requirement. Hidden pairs require tracking where digits appear rather than looking only at cells with few candidates.
What comes after naked and hidden pairs?
Once pairs feel natural, the next step is naked and hidden triples, then X-Wing, and eventually techniques like remote pairs — chains of naked pairs across the grid. Sue de Coq is an advanced variation that builds directly on pairs logic.