Lesson 5 of 9
Naked pairs
Two squares, the same two candidates: those digits belong to them, so erase them everywhere else in the unit.
What this grid does
- Starting digits
- 26 of 81
- Deductions to solve
- 56
- Uses of Naked pairs
- 1
- Digits placed before it is needed
- 7
- First needed at
- deduction 8, in box 5 (R4C4 and R5C4)
- Also calls for
- last free cell, cross-hatching, naked single and hidden single
Measured on this grid by the same solver the hint button uses — how these puzzles are chosen.
Why this one is worth drilling
Roughly 31 puzzles in 100 need it — often enough to meet by accident, rarely enough that most solvers never get fluent. That figure is measured rather than guessed: 30.5% of solvable 22-clue grids over 4,000 digs.
By this point the grid stops yielding placements and starts yielding only eliminations, which feels like no progress at all. You will make three or four deductions in a row that fill in nothing. That is not you going wrong; it is what this level of puzzle is.
Where it sits in the nine
Fifth, and the gateway to the elimination half of the path. It is the easiest of the group-based techniques to see, which is why it opens the half rather than hidden pairs, its harder twin in lesson six. If this one has not clicked, the four that follow will feel arbitrary, because they are all variations on the same move: reason about a set of squares instead of one.
Working it
You need written candidates here — there is nothing to eliminate without them. Annotate a unit fully before looking for the pair, and look along units rather than at the grid: a naked pair is two squares in the same row, column or box, and two matching squares that share no unit mean nothing at all. Watch for the eliminations that do nothing. A genuine naked pair often clears candidates from squares that were never going to matter, and it is easy to conclude the technique "didn't work". Judge it by whether the unit is tidier afterwards, not by whether a digit went in — the placement usually arrives one or two deductions later, somewhere you were not looking.
The full explanation of naked pairs covers the reasoning with diagrams.
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