28 August 2012

When and What to Exchange

The diagram shows a position from one of my recent games. I had just picked up a loose Pawn with 52...Rxa5, to which my opponent replied 53.Ba2. Now I had to formulate a plan to guide me over the next few moves.

Besides Black's extra Pawn, the most striking characteristic of the position is the roster of minor pieces. White has the Bishop pair, but the light squared Bishop is hampered by the Pawns on d5 & e4, which are in turn blockaded by Black's Pawn and Knight. The Knight on e5 is a more effective piece than the light squared Bishop.

Black's obvious plan is to advance the c-Pawn, against which White will fight tooth and nail on the light squares c4 and c2. The question is what roster of the remaining pieces is most advantageous to Black, and what roster is least advantageous. That is the question on which I spent my time.

White to move

Black can start initiating trades with 53...Qb5, which forces a Queen exchange with 54.Qxb5 Rxb5. Then after 55.Rb1, Black can't play 55...Rxb1+, because after 56.Bxb1, comes 57.Bxe5 Bxe5 with opposite colored Bishops, when a draw is certain. This gave me one roster to avoid: Black has to keep some other material on the board besides those mismatched Bishops.

Another continuation I looked at was 53...Qa7 54.Bb1 Ra1 55.Qb5 Qa6 56.Qxa6 Rxa6, exchanging Queens but leaving the Rooks and minor pieces. Note that this variation is not forcing, but just an example that leads to one likely roster of material. A similar example variation is 53...Qa7 54.Bb3 Qb8 55.Rb1 Rb5 56.Qd1 c4 57.Bc2 Rxb1 58.Qxb1, leaving the Queens and minor pieces, when 58...Qa7 avoids the Queen trade.

Which is better for Black -- Queens or Rooks -- with the minor pieces? I decided I didn't understand the position well enough to make this decision, so I played to avoid all exchanges, leaving all pieces on the board. The game continued 53...Qa4 54.Bb1 Qb3. With every move I gained a better understanding of the position and adhered to my strategy of avoiding exchanges. The same material was still present when White resigned ten moves later, facing significant material loss.

One aspect of the position I did understand -- White can't trade the dark squared Bishop for the Knight. In that event, Black's Queen and Bishop cooperate on the weakened dark squares to make serious trouble for the White King.

A rule of thumb tells us to trade pieces when ahead in material. While it might be true in the majority of positions, it isn't necessarily true for all. One case where it fails is with opposite colored Bishops on the board.

No comments: