411 REFERENCE · Wikibooks
Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nc3/3...Nf6/4. Nf3/4...Be7/5. Bf4/5...O-O/6. e3/6...c5
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Queen’s Gambit Declined, Blackburne Variation, Main Line
6...c5
Black immediately strikes the White centre with ...c7-c5. This takes advantage of the Bishop being on f4 instead of g5, which applies less pressure on d5. To demonstrate, after 1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Nf3 Be7 5. Bg5 O-O 6. e3 h6 7. Bh4, 7...c5 can be met with 8. Bxf6 Bxf6 9. cxd5 exd5 10. dxc5, and Black is left with a suboptimal isolated queen’s pawn structure.
White’s only move is the Botvinnik exchange: 7. dxc5, forcing the black bishop on e7 to waste a tempo. 7. cxd5 can be met with ...Nxd5, and 7. Bd3 or 7. Be2 can be met with ...dxc4, which all allow black to equalise comfortably.