Forced win

A forced win exists when a player can guarantee victory even if the opponent chooses the most resistant defense on every turn. The claim does not mean the win is easy, short, or obvious. It means that no legal reply changes the result under perfect play.

A forced mate is one special case: the sequence guarantees checkmate. A forced win may also exist without an immediate mate, for example by winning sufficient material, meaning a decisive amount of piece or pawn value, or by reaching an endgame that cannot be saved. In endgames covered by tablebases, an exhaustive database can prove whether perfect play produces a win, draw, or loss.

The proof may contain several winning moves and different routes. A forced win therefore does not require a single forced sequence, a chain in which the relevant replies are highly restricted, from the start. What matters is that a winning continuation exists against every defense.

It is not synonymous with a winning advantage. Human analysis or a chess engine, a program that examines positions, may judge a position as winning without yet proving every reply. A miscalculation can break the line, while a misevaluation can make a player believe an advantage is sufficient when defensive resources remain. Its counterpart is a forced draw.