A chess game is conventionally divided into three phases: the opening, the middlegame, and the endgame. The opening covers roughly the first ten to fifteen moves and centers on development, king safety, and laying the foundation for later plans. The middlegame is the phase of tactics, attacks, and positional maneuvering, when most pieces remain on the board and dynamic themes dominate. The endgame features few pieces and shifts the focus to king activity, pawn promotion, and precise calculation.
Several guiding principles govern how an opening should be conducted. Players are encouraged to control the four central squares (d4, e4, d5, e5), develop minor pieces (knights and bishops) quickly, castle to safeguard the king, avoid moving the same piece twice in the opening, and connect the rooks by clearing the back rank. Central pieces are prized because they control more squares and reach every part of the board, while tempi—the units of time measured in moves—reward efficiency, since gaining a tempo forces the opponent to waste a move. Over the long run, a player accumulates a personal opening repertoire: a prepared collection of lines for White and Black tailored to their style.
Counter to the classical idea of occupying the center with pawns, hypermodern chess is a school of thought developed in the early twentieth century by Réti, Nimzowitsch, and Tartakower. Hypermodern players allow the opponent to build a broad pawn center and then attack it from a distance with pieces, often after fianchettoing bishops. This philosophy underpins many modern defenses and pairs with the foundational positional ideas laid out in Nimzowitsch's book "My System," where ideas such as prophylaxis—preventing the opponent's plans before pursuing your own—first took systematic shape.