Sudoku technique
Naked pairs
The first technique that removes possibilities instead of placing digits. It feels like less progress than it is: eliminations are what crack open a grid that has stopped giving up cells.
What a naked pair is
A naked pair is two cells in the same row, column or box that have the same two candidates and no others. Neither cell is solved, and you cannot tell which digit goes where — but you know something anyway.
You know those two digits are used up. Whatever order they end up in, that pair of cells consumes both, which means no other cell in the unit can have either of them. The pair locks the digits away.
The shift this represents
Everything before this places digits. Hidden singles tell you a cell’s answer. A naked pair tells you nothing’s answer — it only removes candidates from cells you still cannot solve.
That feels like less progress and is often more. Eliminations are what turn a cell with three candidates into a naked single, or a digit with three homes in a box into a hidden single. Most hard puzzles are unlocked by an elimination rather than a placement.
It is also the first technique that genuinely requires pencil marks. You cannot see a naked pair without candidates written down, which is why the board on this site has a notes mode.
Step 1 of 4
A real position
Part way through a real grid, with the straightforward cells already placed. From here, progress comes from removing possibilities rather than placing digits.
Triples, and why they are harder to see
The same logic scales. Three cells in a unit that between them hold only three candidates are a naked triple, and those three digits leave every other cell in the unit.
The catch is that the cells do not each need all three candidates. Cells holding 1,4, 4,7 and 1,7 are a perfectly good triple on 1, 4 and 7 — no cell shows the full set, which is exactly why triples get missed. Look for three cells whose candidates union to three digits, not three identical cells.
Where to look first
Scan boxes before rows and columns. A box is compact enough to take in at a glance, and pairs inside a box often eliminate along a row or column as well, which pays twice.
After that, the units with the fewest empty cells. A row with four empties and a pair among them is doing far more work than a pair in a row with eight.
When pairs and triples stop producing anything, that is the point to start looking at patterns that span the whole grid, like the X-Wing.
Other techniques
- Hidden singlesThe single most valuable technique in Sudoku, and the one most beginners never quite articulate.
- Hidden pairsTwo digits with only two homes between them in a unit.
- Pointing pairsA digit trapped inside one box, and inside one line within that box.
- All techniquesThe full list, in the order they are worth learning.
Try it on a real board
The free board on the home page has a notes mode, which is what every technique past hidden singles needs. Then take the same eye into a live match.