Ask an intermediate Sudoku solver whether they use Naked Pairs and they'll often say no. Then watch them solve — and within minutes they'll eliminate candidates from a row because two cells both contain only the same two digits. That is a Naked Pair. Most solvers apply the logic instinctively without knowing its name, which means they also don't know how to extend it. Naming the technique, understanding why it works, and deliberately looking for Naked Triples and Quads opens up an entire level of eliminations that instinct alone never reaches.
What a Naked Pair Is
A Naked Pair occurs when exactly two cells in the same unit (row, column, or box) each contain exactly the same two candidates — and no others. Because those two digits must fill those two cells (in some order), they cannot appear anywhere else in that unit. All other occurrences of both digits in the unit can be eliminated.
→ The 3 and 8 in row 5 must go in C2 and C7 (in some order)
→ Eliminate 3 and 8 from all other cells in row 5
→ Also check: if both cells are in the same box, eliminate from that box too
Why the Logic Works
The reasoning is simple: two cells, two digits, one digit per cell. Since each cell can only be 3 or 8, and no digit can repeat in a unit, those two digits are "used up" by those two cells. Any other cell in the unit claiming 3 or 8 as a candidate is wrong — the digit will be placed in one of the pair cells before it could ever reach that other cell.
This logic is the same regardless of which cell ends up containing which digit. You don't need to know which order they resolve — the elimination is valid in both cases.
Extending to Naked Triples
A Naked Triple works by the same principle but involves three cells and three digits. The three cells don't each need to contain all three candidates — they just need to collectively contain exactly three candidates spread among them. If cells A, B, and C in a unit together contain only the digits {2, 5, 9} — in any combination — then those three digits are locked in those three cells, and all other cells in the unit can have 2, 5, and 9 eliminated.
Common Naked Triple patterns include {2,5}, {5,9}, {2,9} (each pair of the three) or {2,5,9}, {2,5}, {5,9}. The three cells don't need to be identical — they just need to have no candidates outside the triple set.
Naked Quads: Rare but Powerful
Naked Quads extend the logic to four cells and four digits. They're rarer than Pairs and Triples but occur in hard puzzles. Four cells in a unit that collectively contain only four specific digits — say {1,4,6,8} — lock those digits into those cells, eliminating them from all other cells in the unit. Because a Naked Quad eliminates four candidates from multiple cells simultaneously, finding one can unlock a significant portion of a stalled grid.
The Hidden Counterparts
Every Naked group has a Hidden counterpart. A Hidden Pair is when exactly two digits are confined to exactly two cells in a unit — even though those cells may appear to have other candidates. The two "hidden" digits must go in those two cells, so all other candidates in those cells can be eliminated. Hidden Pairs are frequently missed because solvers focus on the candidates present rather than asking "where can this digit go?" Combining your Naked and Hidden group scanning — working both cell-focused and digit-focused perspectives — ensures you find everything the grid has to offer before moving to more advanced techniques.