Techniques › Naked Single
Naked Single
A cell with only one candidate left.
A Naked Single is a cell whose peers have eliminated every digit but one. Nothing else fits, so that digit goes in.
It is the mirror image of the Hidden Single: that one is a digit with one home, this is a home with one digit. Naked Singles are easier to verify but harder to find by eye, because spotting one means knowing a cell's full candidate list. Players who keep pencil marks find these constantly; players who scan find Hidden Singles instead.
A worked example
Taken from a real puzzle in our bank, at the point where this was the cheapest move available. Pattern candidates are marked in amber; anything the step eliminates is struck through in red.
| 6 | 1 | 7 | 4 | 249 | 3 | 8 | 5 | 249 |
| 4 | 38 | 58 | 1 | 259 | 6 | 379 | 379 | 239 |
| 39 | 29 | 25 | 7 | 8 | 45 | 13 | 14 | 6 |
| 78 | 45 | 3 | 9 | 457 | 1 | 2 | 6 | 58 |
| 179 | 29 | 12 | 3 | 6 | 58 | 4 | 79 | 58 |
| 789 | 45 | 6 | 458 | 457 | 2 | 379 | 379 | 1 |
| 5 | 36 | 4 | 2 | 13 | 7 | 1369 | 8 | 39 |
| 13 | 7 | 18 | 4568 | 45 | 9 | 36 | 2 | 34 |
| 2 | 368 | 9 | 68 | 13 | 48 | 5 | 14 | 7 |
- NudgeOne cell has only a single candidate left.
- WhereNaked Single: r1c4
- Do itr1c4 = 4
How to spot it
If you keep pencil marks, look for a cell with a single mark. If you do not, check cells at the intersection of busy rows, columns and boxes — a cell whose three houses are well filled has few candidates left.
Where you will meet it
Naked Single sits at tier 0 of our ladder, which means it first becomes necessary at Very Easy. Puzzles below that band never require it, though it may still appear as a shortcut.
Read next
- Hidden Single A digit with only one home left in a house, even though that cell has other candidates.
- Naked Pair Two cells in a house holding the same two candidates lock those digits away from the rest.