Naked pairs in sudoku
The naked pair is the first candidate pattern most players learn, and the one that keeps working at the top of the ladder. Two cells in one unit, holding the same two candidates and nothing else, claim both digits between them. Everything else follows from counting.
The pattern
Sweep a row, column or box for two cells wearing identical two-digit pencil marks. In the row below, two cells hold 2 and 7 and nothing else. One of them takes the 2 and the other takes the 7. The order stays unknown, and it does not matter: both digits are consumed either way.
The board shows its work. The marked row misses 2, 6, 7 and 9, and its outer empty cells hold all four candidates. The pair cells hold two, and the placed 6s and 9s standing in their columns explain the difference: each pair cell watches a 6 and a 9 elsewhere in its column, so only 2 and 7 remain for them.
The elimination
Two digits filling two cells leave nothing for anyone else. Every other cell in the unit drops both digits from its candidates:
Follow the aftermath on this row and you see why pairs matter. The outer cells fall from four candidates to two, becoming a 6-9 pair of their own, and a solver watching the crossing columns now has far less to track. Pairs rarely solve a cell on the spot. They shrink the search, and shrinking the search is most of sudoku.
How to hunt
Fill your candidates first; the pattern lives in complete marks. Tap Auto notes, then sweep unit by unit for matching two-candidate cells. Rows and columns scan in a straight line, boxes need a small circular glance, and the whole pass over a board takes under a minute once the eye knows the shape.
Two-candidate cells are worth noticing even without a twin. Solvers call them bivalue cells, and they fuel the XY-wing and the chains above it, so a mental map of where they sit keeps paying after the pair hunt ends.
Near misses
The pair must be exact. Same row, one blocking digit removed:
Two cells that merely share some candidates prove nothing; the claim needs exactly two candidates in each. The reverse trap bites too: a stale mark you forgot to erase can disguise a real pair as a broken one. Auto-remove notes is on by default here and keeps placed digits sweeping your marks clean, so the pattern you see is the pattern that exists.
Triples
Three cells in a unit drawing from the same three digits form a naked triple, and the cells need not each hold all three candidates. Cells showing 2-5, 5-8 and 2-8 lock up 2, 5 and 8 as firmly as three full triplets would. Triples hide better than pairs for exactly that reason, and they mark the boundary where medium puzzles hand over to hard ones on this site.
Frequently asked questions
What is a naked pair in sudoku?
Two cells in the same row, column or box that hold exactly the same two candidates and nothing else. One of them takes each digit, order unknown, so the two digits are spoken for and every other cell in that unit loses both as candidates.
Why does a naked pair let me remove candidates?
Count the cells. Two digits must fill two cells, and the pair cells accept nothing else, so between them they consume both digits completely. Any other cell in the unit that kept one of those digits penciled in is holding a candidate that can no longer come true.
What is a naked triple?
The same argument with three cells and three digits. The cells need not each hold all three candidates; they only need to draw from the same set of three. Three cells, three digits, fully claimed, and the rest of the unit sheds all three.
When should I look for naked pairs?
Right after filling candidates, while the picture is complete. Tap Auto notes, then sweep each row, column and box for two cells wearing identical two-digit marks. On our puzzles the habit starts paying at medium, where a pair or locked candidates is guaranteed to be the key move.