Modern Defense, Averbakh System

The Averbakh System of the Modern Defense can be reached by 1.d4 d6 2.c4 g6 3.Nc3 Bg7 4.e4. Other move orders begin with 1.e4. White occupies the center with three pawns, while Black develops the bishop to g7 through a fianchetto, meaning the g-pawn advances and the bishop is placed behind it on a long diagonal.

The sequence is written in algebraic notation: squares such as e4 combine a column letter and row number; N means knight, B bishop, R rook, and Q queen; pawn moves normally show their destination, x marks a capture, and + marks check. Moves are read in pairs, White first and Black second; dots before a move shown alone indicate Black's turn.

White gains space, meaning control of more squares and greater freedom for the pieces behind the pawns. That same center can become a target. Black commonly attacks it with pawn breaks such as ...e5, ...c5, or, in some lines, ...f5: advances intended to challenge White's pawns and open paths for the pieces.

It is called a system because the same pawn formation can arise through several move orders and Black retains several choices for the g8-knight. It may go to f6, e7, or h6 according to the position. If Black eventually plays ...Nf6, the game may transpose, meaning that a different move order has reached a familiar position. Some lines resemble the King's Indian Defense or the Benoni, other openings in which Black initially allows White more central space and then attacks the white pawns.

White should not advance every central pawn automatically. A large center needs piece support and may collapse if it opens before the king is safe. Black cannot simply wait either, because White's space may become a lasting advantage. The Pirc Classical Variation shares the idea of allowing White a center, but includes an early ...Nf6 and creates different choices.