The deeper you delve into the mysteries of your game, the rarer the aha moments become. Here’s one I enjoyed some time ago.
Being an exchange down in a theoretical position from the Tarrasch System of the French Defense it seemed to me that Black should avoid exchanges. That’s what we do in general when material down, right? I very much wanted to play 18…Db6 in order to keep it as complex as possible.
Why my database gave 18…Bc5 as the main move (with good results for Black) seemed puzzling to me. Shouldn’t we use our queen to create play while his queen is offside in the corner, doing nothing? But the database also showed the poor results of 18…Qb6 when it had been played by respectable chess masters (never by top players, though).
At that point a chess coach would have come in handy, but none was available. So I studied annotated games in this line (1. e4 e6 2. d4 d5 3. Nd2 Nf6 4. e5 Nfd7 5. Bd3 c5 6. c3 Nc6 7. Ne2 cxd4 8. cxd4 f6 9. Nf4 Nxd4 10. Qh5+ Ke7 11. exf6+ Nxf6 12. Ng6+ hxg6 13. Qxh8 Kf7 14. O-O e5 15. Nb3 Nxb3 16. axb3 Bf5 17. Bxf5 gxf5 18. Bg5) in order to solve the mystery myself. After a while it sunk in eventually.
18…Bc5 is the much better move indeed.
Black actually wants the queens to be exchanged!
Let me encourage you to figure out why for yourself before you continue reading.
Once you’ve been told it’s simple.
A trade of queens will make the black king a powerful piece in the resulting endgame. The already centralized king can then be used to support Black’s central pawns that compensate for the exchange.
With queens still on the black king can’t do anything, it will always be harrassed by the white queen. With queens exchanged Black gains a powerful helper for the endgame.
Some quick remarks on the opening:
With the Tarrasch move 3.Nd2 White denies himself pressure on the center (d5). My chess understanding tells me that 3…c5 exploits the downside of Nd2 and must be the best response in order to equalize. I do, however, only play the French against weaker opponents in order to create winning chances with Black. While the positions after 3…c5 are often somewhat bloodless and drawish, the more risky 3…Nf6 guarantees a rich game.
9.Nf4 is a sideline that is said to be not overly dangerous for Black. White wins an exchange, but Black’s pawn center should give him sufficient compensation (especially if you understand when to trade queens and when not!).
Play until move 18 represents the mainline, the position has been reached dozens of times in (grand)master level OTB play. There are alternatives along the way, but I don’t know this stuff well enough to assess them. For instance White has tried 15.Nf3 instead of Nb3, and at move 16 Black may want to consider 16…Be6 and 16…e4 instead of 16…Bf5.