Sudoku Candidates: Possibility Is Not the Same as Truth

Pencil marks are deliberately provisional. They describe what has not yet been ruled out, not what belongs in the cell.

Keeping that distinction clear protects the puzzle from the most common form of accidental guessing.

Define possible

A candidate is possible when it does not conflict with the current givens and confirmed entries. Several candidates can be possible at the same time.

Define forced

A candidate becomes forced when every alternative is eliminated by a unit, a pattern or a chain. The reason must be visible in the current state, not inferred from what you hope the solution will be.

Use notes as questions

Write “could be 2 or 7” rather than mentally choosing one. The note keeps both branches available while you search for a relationship that decides between them.

Treat colours carefully

Automatic highlighting can show that a number is legal, but legality is not proof. Use interface feedback to locate peers, then do the logical check yourself.

Place only with a reason

Before entering a final digit, say “only candidate in this cell” or “only place for this digit in the box”. If you cannot complete that sentence, leave it as a note.