Key ideas
- The pin adds to Black's control of e4 and d5. Black is often ready to give up the bishop for the knight, either to double White's pawns or to gain time against the centre.
- 5.Bg5 is the main test. The steadier answer is 5...h6 6.Bxf6 Qxf6 7.e3 O-O 8.Rc1 dxc4 9.Bxc4 c5, where Black has the bishop pair and White a small lead in development.
- The Vienna Variation, 5.Bg5 dxc4, is the sharp option. After 6.e4 c5 7.Bxc4 cxd4 8.Nxd4 Bxc3+ 9.bxc3 Qa5, the position is open and tactical, with White's centre and lead in development against Black's pressure on the weakened c3 pawn.
- Quieter choices are 5.cxd5 exd5 6.Bg5, a Carlsbad structure in which Black's bishop is better placed on b4 than on e7, and 5.Qa4+, the Alekhine Variation, which makes Black spend a move blocking the check.
Plans for White
In the 5.Bg5 h6 6.Bxf6 lines, use your lead in development quickly with Rc1 and Bxc4 before the bishop pair starts to tell. In the Carlsbad structure after 5.cxd5, the minority attack and the e4 break are the usual plans.
Plans for Black
Play actively. ...dxc4 followed by ...c5 is the typical way to hit the centre, and the bishop pair after Bxf6 makes up for slower development. In Carlsbad positions, the bishop on b4 and the ...Ne4 jump make Black's game easier than in the standard Exchange Variation.
For the wider picture, see the Queen's Gambit Declined guide.