Line

A line is one specific path of moves: a player's option, the opponent's reply, and the continuations assumed after it. It may contain only one or two moves or extend much farther. Every step depends on the previous one, so changing a reply creates a different sequence.

Within a calculation tree, a line follows one path among several possibilities. A branch appears when an alternative is considered at some point. The main line is the sequence an analyst considers most important; for a chess engine, a program that examines positions, the principal variation is the sequence it currently estimates as optimal.

A line is not a guaranteed prediction unless every reply is forced. The opponent may deviate and require new analysis. In opening preparation, which studies the game's beginning in advance, “line” can also mean a sequence known from earlier games and analysis. Different sequences can reach the same position through a transposition.

To study a line clearly, state the starting position, follow the moves in order, and end with an evaluation of the resulting position, meaning a judgment of which side stands better and why. A move list without that conclusion shows what might happen but not whether the sequence favors either side.