What does X mean?
X means two items cannot match. That fact may come from a direct negative clue, the consequence of another confirmed match, or a cross-category deduction.
X does not mean 'I do not know.' You should be able to justify why the pairing is impossible before marking it.
What does O mean?
O is a confirmed match. It says the two items belong together in the final solution, so it has stronger consequences than a single X.
Once O is placed, competing options in the same row and column are eliminated. The web grid may add those X marks automatically, but the logic is the same.
What does a blank cell mean?
A blank cell is still possible but unproven. It is neither positive nor negative information. One of the most common mistakes is turning 'probably' into O.
Leaving a cell blank is correct when the evidence is incomplete.
Why does O close other cells?
Logic grids use one-to-one matching. If Cem is confirmed as Blue, Cem cannot take another color and Blue cannot belong to another person.
This simple rule turns one O into several X marks and often exposes the next forced match.
A good marking order
Place the mark directly supported by the clue, propagate its consequences, process any newly forced matches, and only then move to the next clue.
- Negative fact → X
- Confirmed match → O
- Competitors after O → X
- One option left → O
- No proof → leave blank
A tiny example
Suppose Cem can be White, Blue, or Gray. If White and Gray are eliminated, those two X marks force Blue to O. Once Blue is confirmed for Cem, every other person's Blue cell becomes X.