Candidate
A value can remain in a note only when row, column, and box all permit it.
Sudoku candidate notes
Notes are not a shortcut.
Notes are not a shortcut.
They are a visible promise.
Candidate notes turn a vague feeling that a cell might be 2, 5, or 8 into a record you can test against every row, column, and 3×3 box. Used honestly, they make difficult Sudoku easier to inspect without turning a logical solve into a guess.
2·5·8candidate setthree constraintsone legal value remains
Candidate-note method
Record only what the board permits now.
For an empty square, list the digits that do not already appear in its row, column, or box. This is the whole candidate-note rule. A note is removed when a later placement makes it impossible; it becomes an answer only when every alternative disappears.
This approach is especially useful once Easy placements thin out in Medium, Hard, and Killer Apex. It keeps the solve explainable: every number has a visible reason to be there.
- 01Start small
Use notes in one busy box or a small group of uncertain cells instead of filling the whole board indiscriminately.
- 02Update after each move
A correct placement changes neighbouring candidate sets. Remove only candidates that now conflict.
- 03Look for a single
If a cell has one candidate, or a digit has one legal home in a unit, the note has become a deduction.
Notes versus guessing
The aim is proof, not speed.
A candidate note reduces uncertainty; it does not declare an answer.
Placement
A value enters the board when all other candidates are eliminated.
Revision
If a test fails, return to the last confirmed deduction rather than inventing a new path.
Next useful guide
Read Sudoku strategies →Notes create the field. Strategies reveal its structure.
Learn how singles, pairs, and box-line interaction use an accurate candidate record to produce the next reliable move.