Naked Pair

The pattern

Find two cells in the same row, column or box whose candidate lists are both exactly the same two digits — say 4 and 7. You do not know which cell takes which, and you do not need to. Between them, those two cells will consume both the 4 and the 7 of that unit.

That means no other cell in the unit can be a 4 or a 7. Erase those candidates everywhere else in the unit. This is usually the first real elimination a player learns.

How to spot one

Work unit by unit and look only at cells with exactly two candidates — ignore everything else. Two such cells in the same unit are a pair if their lists match. Three cells with two candidates each are not a naked pair unless two of them match exactly; if all three share three digits between them, you are looking at a naked triple instead.

A pair that sits inside a box and also shares a row is worth a second look: it eliminates along the row as well, and it often sets up a pointing elimination immediately afterwards.

Why it is valid

Two cells, two digits, and each digit must appear once in the unit. If any third cell took the 4, then both pair cells would be forced to 7, which would put two sevens in the same unit. The contradiction is immediate, which is why this elimination is safe even though you never learn which cell holds which digit.

What it usually unlocks

A naked pair rarely finishes a puzzle by itself. It trims two or three candidates elsewhere, and one of those cells then becomes a naked single or a hidden single. On Hard puzzles here, one or two eliminations of this kind are exactly what stands between a stalled grid and a finished one.