Naked Pair

If two cells in a row, column or box hold the same two candidates and nothing else, those two digits can be removed from the rest of that unit.

Level: Intermediate · technique 6 of 7

When to use it

The pair technique you will meet most often once you keep pencil marks. When a cell has only two candidates, check whether another cell in the same unit has exactly the same pair.

The two cells must share the two digits between them. You may not know which goes where, but you do know neither digit can go anywhere else in the unit.

How to find it

1. Find a cell with exactly two candidates.
2. Look in its row, column and box for another cell with exactly the same two.
3. Note which unit the two cells share. If they share both a line and a box, the pair works in both.
4. Remove both digits from every other cell of that unit.

Worked example

On the board below, look at r5c1, r6c1 in column 1.

1. R5c1, r6c1 both have only 6, 7 as candidates.
2. Both are in column 1, so one of them is 6 and the other is 7. Which is which does not matter yet.
3. So no other cell of column 1 can be 6 or 7. Removed: 6 from r7c1, 6 from r9c1.

Common mistakes

• The two cells must match exactly: (2, 5) and (2, 5, 7) are not a pair.
• Do not remove anything from the two pair cells themselves.
• The cells must share a unit. Two cells on a diagonal tell you nothing.