Naked pair

When two cells in a row, column, or box have exactly the same two-candidate set — say {3, 8} — those two digits are 'locked' into those two cells. Whichever 3 and 8 end up where, no other cell in the unit can be a 3 or an 8.

Naked pair is the gateway to subset reasoning. Once you see one, you'll spot triples and quads with the same logic.

When to look for it

Keep pencil marks tight. Naked pairs appear when two cells in a unit have been reduced to the same two options. Cross-check the rest of the unit and erase those two digits everywhere else.

How to apply it

1. Find two cells in the same row, column, or box that both have exactly the same two candidates.
2. Remove those two digits from every other cell in the unit.

Example