You have filled in every obvious cell, you have scanned the grid in every direction, and nothing moves any more. No cell can be deduced directly. That is precisely the moment the naked pair steps in.
It places no digit at all, and that is what puzzles most beginners. It eliminates. But those eliminations trigger the next ones, and step by step the grid starts moving again.
The exact definition of the naked pair, how to apply it in a row, a column and a box, the special case of the double elimination, and the Domino33 method for spotting one in seconds.
🎬 The Domino33 video on naked pairs
Here is the full tutorial, with the theory first and then worked examples on real grids.
▶ English audio track and English subtitles: pick either from the ⚙️ icon.
Did this video help? Over 120 free Sudoku tutorials are waiting for you on the channel.
▶ Subscribe for freePart 1
What exactly is a naked pair?
The definition fits in one sentence:
Two cells of the same unit (row, column or box) that contain exactly the same two candidates, and nothing else.
The reasoning that follows is watertight. Those two digits have to be placed somewhere in the unit. They can only go in those two cells. So they will occupy both of them, in one order or the other. Which order does not matter: those two digits are now forbidden everywhere else in the unit.
A worked example
Here is a row from a grid. Look at cells C2 and C6:
C2 and C6 contain nothing but {3, 8}. The 3 and the 8 of this row will therefore occupy those two cells. As a result, the 3 disappears from C3, and the 8 disappears from C5 and C7.
C3 goes from {2,3,9} to {2,9} · C5 goes from {2,4,8,9} to {2,4,9} · C7 goes from {4,7,8,9} to {4,7,9}
Look at what just happened in C3: only {2, 9} is left. A new naked pair has appeared, one you would never have seen without the first. That domino effect is what makes the technique so valuable.
After every elimination, read the unit again straight away. A naked pair very often creates another one, or reveals a cell with a single candidate. Chaining on the spot saves a great deal of time.
Part 2
In a row, a column and a box
The reasoning is exactly the same in all three units. Only the elimination area changes:
- In a row: the 9 cells of one horizontal line
- In a column: the 9 cells of one vertical line
- In a box: the 9 cells of one 3×3 square
The golden case: double elimination
Sometimes the two cells of the pair sit in the same row and in the same box at once, or in the same column and the same box. In that case you eliminate in both units simultaneously.
A naked pair in C1 and C3 of the first row, for instance, belongs to row 1 and to the top-left box. You then clean 13 cells instead of 7. These configurations are by far the most rewarding, so look for them first.
Do not look only for adjacent cells. The two cells of a naked pair can sit at opposite ends of the row. The only requirement is that they share a unit, not that they touch.
Part 3
The search method
Step 1, Pencil in your candidates
Without written candidates, no naked pair is visible. It is an absolute prerequisite, and it is certainly not cheating, whatever many solvers still believe.
Step 2, Spot every cell with 2 candidates
Scan the grid and mark, mentally or with a dot in the margin, every cell left with only 2 candidates. Those are your only contenders. A cell with 3 candidates can never be part of a naked pair.
Step 3, Compare the ones sharing a unit
For each 2-candidate cell, look at the other 2-candidate cells in its row, its column and its box. If you find exactly the same couple of digits, you have a naked pair.
Step 4, Eliminate, then read again
Remove both digits from every other cell of the unit concerned. Then go through the unit again from the start, because you may just have opened up another one.
Start with the fullest units, the ones with only 3 or 4 empty cells left. Candidates are few there, 2-candidate cells abound, and naked pairs turn up within seconds.
What comes next?
The naked pair has two natural extensions. The naked triple, where three cells share three candidates, follows exactly the same logic. And the hidden pair, its exact mirror image: where the naked pair cleans the outside, the hidden pair cleans the inside.
🎬 See the method in action
In the video the technique is worked through step by step on real grids. It is the fastest way to build the reflex.
Exercise
Your turn
Here is another grid row, with a naked pair different from the one in the example.
First spot the two cells holding only the same two candidates.
Part 4
Practice quiz
Four questions to check what you have learned. Good luck!
❓ Frequently asked questions
A naked pair is two cells of the same unit (row, column or box) that contain exactly the same two candidates and nothing else. Those two digits will necessarily occupy those two cells, in one order or the other. They can therefore be eliminated from every other cell of the unit.
No. The two cells can sit anywhere in the unit, several cells apart. The only requirement is that they belong to the same row, the same column or the same box.
The naked pair is visible: two cells contain only the same two candidates, and you clean the other cells of the unit. The hidden pair is concealed: two digits appear in only two cells, but those cells also hold other candidates, and it is the inside of those two cells that you clean.
That happens often and is perfectly normal. A naked pair only helps if its two digits are still candidates elsewhere in the unit. If they are not, the configuration exists but is sterile: move on to the next unit rather than forcing it.
📋 Summary
Naked pair essentials
- Setup: 2 cells of the same unit holding exactly the same 2 candidates
- Action: eliminate those 2 digits from every other cell of the unit
- Prerequisite: having pencilled in your candidates, without which nothing is visible
- Starting point: spot every cell with exactly 2 candidates
- Golden case: the 2 cells share the row and the box, so 13 cells get cleaned
- Related techniques: naked triples, hidden pairs, Pointing Pairs
The naked pair is the gateway to all Sudoku logic. Once the reflex is there, hidden pairs and then the advanced techniques all rest on the same work of reading candidates.
📘 Go further with the Domino33 books
Naked pairs and every other technique on this site are covered step by step in the Domino33 memento, available in English.
