When two cells in the same unit share exactly the same two candidates, those two digits can be eliminated from other cells in that unit.

A Naked Pair occurs when two cells in the same row, column, or block contain exactly the same two candidate digits and no others. Since these two digits must occupy those two cells, they can be eliminated as candidates from all other cells in the same unit.

Principle and Application

For example, if two cells in a row both have only candidates {3, 7}, then 3 and 7 must go in one of these two cells. Therefore, no other cell in that row can contain 3 or 7. This elimination often creates Naked Singles in other cells.

Tips for Spotting Them

Identify all cells with exactly two candidates, then check whether any pair in the same unit shares the same candidates. Accurate pencil marks are a prerequisite. This technique is essential for solving Hard-level puzzles.