gewgaw wrote on 08/29/10 at 13:42:19:
1. c4 c5 2. Nf3 Nf6 3. Nc3 Nc6 4. d4 cxd4 5.
Nxd4 g6 6. g3 Bg7 7. Bg2 O-O 8. O-O Nxd4 9. Qxd4 d6 10. Qd3 a6 11. Bd2
Maybe a good opportunity to explain 11.Bd2?
We'll start from worst to best:
11. b3 Bf5! and white has tactical issues.
11. h3 is too slow and ...b5 comes quickly.
11. c5 is thematic, but allows black easy equality after 11...dxc5 12. Qxd8 Rxd8 13. Be3 Be6.
11. Bf4 does nothing to help white's queenside ambitions, the move just "hits air". Black will achieve full equality with the ...b5 break.
11. Bg5 is perhaps the most famous continuation, but does nothing to aid white's queenside ambitions and black's eventual ...b5 break equalizes just as easily as it does versus 11. Bf4.
11. Be3 Ng4 is slightly awkward for white, but this is is the second best continuation.
Finally that brings us to the prophylactic 11. Bd2.
11. Bd2 works against both Qa5 ideas, and Bxc3 ideas, the latter freeing up the white Q. It is also
the most useful move for white's queenside ambitions because quite often it ends up supporting the desirable b4 push, which is used to highlight either a weak black pawn on b5 after an eventual ...b5 cxb5 axb5, or to support a passed white b-pawn.