Thursday, October 15, 2009

Relative values

Anyone who studies a beginner's book on chess quickly learns that not all pieces have the same value. In my day the most common table of values went as follows: Pawn = 1 point; Knight = 3 points; Bishop = 3 points; Rook = 5 points; Queen = 9 points. Other tables have slightly different values for the bishop and the queen, but the overall ratios are very similar.

Based on this table, exchanging a rook for two minor pieces is considered advantageous because 6 points is more than 5 points. When such an opportunity arises it is a good idea to take a hard look at the resulting position and see if it is actually favourable. In chess it is not just the presence of pieces on the board that counts. Their location and relevant capabilities can be far more important.

I am playing Black in the diagram position and my opponent's last move was the weakening 20.g3-g4. I saw an opportunity to exploit this move by bringing one of my knights into an attacking position. There was an apparent drawback in that my opponent could give up one of his rooks for both of my knights, which according to the table would mean a net loss of 1 point. However in the resulting position there would be a strong manoeuvre available, one that my opponent had not foreseen.

20...Nge5! 21.Rxe5 Nxe5 22.Qxe5

So far, so good, thinks White; he has won two pieces for a rook.


This forces the White knight on b5 to an offside position and prepares to exchange off his colleague on d4. The preliminary pawn move is important because otherwise my opponent would maintain a knight on d4, giving him much better defensive chances.

23.Na3 Bxd4! 24.Qxd4

White could also play 24.cxd4 but then Black carries on with 24...Qxg4+ 25.Kf1 Qh3+ 26.Ke2 Re6, winning White's queen.

24...Qxg4+ 25.Kf1 Re8!

Also possible was 25...Qh3+ 26.Ke2 Re8+ 27.Kd1 Qf1+ 28.Kc2 Qxa1, but I preferred the text move, slamming the door on the opposing king. White has nothing better than 26.Qxd5+ Kh7 27.Qg3, but then follows 27...Qe2+ 28.Kg1 Rg6, a pleasing echo of the line in the previous note.

After a few minutes my opponent agreed he had no defence and resigned the game (0-1).

No comments:

About Me

My photo
Port Coquitlam, British Columbia, Canada
National master (Canada) since 1984. B.C. Champion 1977 and 1984. Runner-up 1991 and 2002. B.C. Open Champion 1972 and 1982. B.C. U/14 Champion 1964-65-66. Mikhail Botvinnik once wrote that publishing your analytical work forces you to be accurate because it exposes you to criticism. Hence this blog.