The Middlegame is the game phase which happens after the opening, where the game of chess literally starts after developing most minor pieces and to prepare or already achieve castling. Quite often due to (double) pushes of the center pawns, the basic pawn structure is often already determined during the first moves, sometimes with center rams involved, already defining which bishop is good or bad.
Opening versus Middlegame
The early middlegame does not necessarily imply a reduction of material by trading pawns or pieces. On the other hand, early pawn trades or other captures don't necessarily imply the beginning of middlegame as long as other aims of the opening are not achieved. Tapered eval for a smooth transition between game phases by multiple piece-square tables does usually not distinguish between opening and early middlegame with all or most material still on the board. Therefor some programmers apply special opening knowledge inside their evaluation to avoid too early queen activity or moving developed pieces multiple times while other minor pieces are still on their home square and have not moved yet (considering returning bishop). Other programs purely rely on the opening book and don't care to differentiate between these early phases.
- Albrecht Heeffer (1984). Automated Acquisition on Concepts for the Description of Middle-game Positions in Chess. Turing Institute, Glasgow, Scotland, TIRM-84-005
- Alex van Tiggelen (1991). Neural Networks as a Guide to Optimization - The Chess Middle Game Explored. ICCA Journal, Vol. 14, No. 3
- Miroslav Kubat, Jan Žižka (2000). Learning Middle Game Patterns in Chess: A Case Study. Lecture Notes in Computer Science, Vol. 1821, Springer
- Шахматы в искусстве (22 часть) BAK Samuel by Valerij Surkov