Sometimes you cannot solve a cell yet — but you can still learn something powerful.
A Naked Pair is two cells in the same house that both contain only the same two candidates, like {5,6} and {5,6}. You do not know which cell gets which digit. You *do* know those two digits are reserved for those two cells.
Why it works
There are only two possible endings:
• Cell A = 5 and Cell B = 6, or • Cell A = 6 and Cell B = 5.
In both endings, 5 and 6 are used up inside the pair. No other cell in that house can also be 5 or 6 — that would force a repeat.
Coach connection: turning a Hidden Pair into a Naked Pair (strip the extras) is step one; cleaning the rest of the house is step two — the same ownership idea, found from the cell side.
How to spot it
Notate the most restricted cells first (cells that see many big digits). After a Hidden Pair strips extras, you often get a Naked Pair next.
Demonstration
You already know Naked Singles: one cell, one candidate. Keep shrinking candidates…
…further… and further… until two cells in the same house both show only the same two digits — here 3 and 6. That is a Naked Pair.
Imagine both possible swaps: one cell gets the first digit and the other gets the second — or the reverse. Either way, the pair uses up both digits.
(If you found this via a Hidden Pair first: stripping extras turned those two cells into this Naked Pair. Same ownership, different door.)
Therefore 3 and 6 cannot appear in any other cell of this house. Remove them from those neighbors (red). You still might not fill the pair — but both worlds already cleaned the house.
Example 1
In one house, find two cells that both contain only the same two candidates.
These cells are a Naked Pair on 5 and 7. They own those digits.
Erase 5 and 7 from every other cell in the house (red). Why? Both possible fillings of the pair use up those digits.
Example 2
In one house, find two cells that both contain only the same two candidates.
These cells are a Naked Pair on 3 and 5. They own those digits.
Erase 3 and 5 from every other cell in the house (red). Why? Both possible fillings of the pair use up those digits.