The most critical line of the Semi-Slav, in the position which arises after 1 d4 d5 2 c4 c6 3 Nf3 Nf6 4 Nc3 e6 (along other move orders), is 5 Bg5. This is the most critical move, because White aims to develop his dark-squared bishop as actively as possible, in defiance of Black’s threat to take – and keep – the pawn on c4.
If Black just develops with …Be7, …O-O etc. he will get an inferior version of the Queen’s Gambit Declined, where he is prematurely committed to the move …c6. While this line is not unplayable, it is not Black’s best approach and also is not likely to appeal to Semi-Slav players who are looking for something more active.
Black’s critical responses are therefore those that try to exploit the downsides of 5 Bg5.
The Botvinnik Variation (5…dxc4)
This is the classic response to 5 Bg5. The main line goes 5…dxc4 6 e4 b5 7 e5 h6 8 Bh4 g5 9 Nxg5 hxg5 10 Bxg5 Nbd7. This leads to massive complications. There are two sidelines of note: 9…Nd5 and 10…Be7. The former (9…Nd5) is nowadays regarded as highly dubious, but the latter (10…Be7) has received some recent attention and seems to be a viable alternative to 10…Nbd7.
A more detailed look at these lines is out of the scope; see the Bibliography for more information. Note:
- 10…Nbd7 is advocated by Shankland in his Chessable Course as an alternative to his main recommendation.
- 10…Be7 is advocated by Cheparinov in his Modern Chess Course, and by Arjun in his Chessable Course.
The Moscow Variation (5…h6)
This is a sound alternative to 5…dxc4. Its main defect is that it allows White to choose the kind of game that arises: positional (6 Bxf6) or tactical (6 Bh4).
A more detailed look at these lines is out of the scope; see the Bibliography for more information. They are is analysed by Dreev and Schandorff in their books, and advocated by Sethuraman in his Chessable Course.
The Cambridge Springs Variation (5…Nbd7 6 e3 Qa5)
While in general attempts to take play into the Queen’s Gambit Declined lead to an inferior version, as in most cases Black does not commit to …c6 this early, there is one notable exception to this: the Cambridge Springs Variation. This line is based on playing …c6 so that Black can follow up with …Qa5, breaking the pin and causes White some immediate problems. The move 5….Nbd7 6 e3 Qa5 is a solid line, but not quite in the Semi-Slav spirit; also, White is able to sidestep the Cambridge Springs entirely and go into a reasonable version of the Exchange Variation with 6 cxd5, because Black is committed to …Nbd7, blocking the bishop on c8 in for the moment.
The line is Shankland’s main recommendation against 5 Bg5 in his Chessable Course.