The Naked Pair strategy is a classic "Double Candidate" technique. It is the natural next step after mastering single-candidate strategies.
A Naked Pair happens when you find two cells in the same group (row, column, or box) that contain only the same two candidates.
Because these two cells must eventually hold those two numbers (we just don't know which is which yet), those numbers cannot appear anywhere else in that group.
Interactive Example
Click "Apply Logic" to see the strategy in action.
Real Example Explanation
In the interactive example above, look at Row 3 (the third row from the top):
- Spot the Pair: Look at the first cell (R3C1) and the fourth cell (R3C4).
- Check Candidates: Notice that both cells have exactly the same two pencil marks: 6 and 9.
- The Logic: One of them is a 6, and the other is a 9. There is no room for anything else.
- The Elimination: Since 6 and 9 are "locked" into these two spots, they cannot exist anywhere else in Row 3. We can safely remove the candidate 6 from the cell in between them (R3C2), highlighted in Red.
How the Logic Works
Imagine you have two friends, Alice and Bob, and there are two chairs reserved for them. You don't know who sits in which chair, but you know for a fact that Alice and Bob will occupy those two chairs.
Therefore, nobody else can sit in those chairs. And conversely, Alice and Bob cannot sit anywhere else.
In Sudoku:
* If Cell A can only be 1 or 2.
* And Cell B can only be 1 or 2.
* And they share a row.
* Then 1 and 2 are taken by A and B. You can erase 1 and 2 from the rest of that row.
How to Spot Them
- Scan for Bi-Value Cells: Look for cells that have only two pencil marks written in them.
- Check for Matches: If you find a cell with
3, 8, scan its row, column, and box for another cell that contains only3, 8. - Verify the Unit: Ensure both cells share a common region (Row, Column, or Box) so they "see" each other.
Why is it called "Naked"?
It is "Naked" because the pair is the only thing in those cells. The candidates are exposed, not hidden amongst other numbers. (Compare this to a Hidden Pair, where the pair is buried inside cells with other candidates).
Related Strategies
- Naked Single: The simpler version with just one number.
- Naked Triple: The same logic applied to three numbers in three cells.
- Hidden Pair: The opposite logic—finding a pair that is hidden by other noise.