Obvious Pairs
A core Sudoku solving technique for intermediate players
An Obvious Pair (also called a Naked Pair) occurs when exactly two cells in the same unit (row, column, or box) each contain the same two candidates and no others. Because those two digits must occupy those two cells - In some order - They can be eliminated from every other cell in that unit.
This technique doesn't tell you which of the two digits goes in which cell. It tells you that no other cell in the unit can hold either of those digits.
Step-by-step guide
- Fill in candidate notes for all empty cells.
- Look for any two cells in the same unit that each contain exactly the same two digits (e.g., both cells show only {3, 7}).
- Those two digits are "locked" into those two cells for that unit.
- Remove both digits from the candidate lists of all other cells in the same unit.
- Check if the removal creates new Obvious Singles or further pairs.
Naked Pair vs Hidden Pair
| Obvious (Naked) Pair | Hidden Pair | |
|---|---|---|
| What you see | Two cells each with only those two candidates | Two cells share two candidates, but have other candidates too |
| Action | Eliminate the pair digits from all other cells in the unit | Eliminate all other candidates from the two cells |
| Difficulty | Easier to spot | Harder to spot (requires scanning by digit, not by cell) |
Extension: Obvious Triples and Quads
The same logic extends to three cells sharing three candidates (Obvious Triple) or four cells sharing four candidates (Obvious Quad). These are rarer but follow identical logic: if N cells in a unit collectively contain exactly N candidates, those candidates are locked in those cells and can be removed from all peers.