The final move order for reaching the Semi-Slav I want to consider runs 1 d4 Nf6 2 c4 e6 3 Nf3 d5 4 Nc3 c6. I refer to this move order as the Nimzo move order, as it involves playing the Nimzo-Indian in combination with the Semi-Slav.
The position after 1 d4 Nf6 2 c4 e6 3 Nf3 d5 is the same as the one reached via 1 d4 d5 2 c4 e6 3 Nf3 Nf6; I have already considered White’s alternatives to 4 Nc3 in my previous post. In this post I’d like to consider the White’s alternatives on moves 3 and 2 that Black needs to be prepared to meet.
The first alternative, and the most important, is 3 Nc3. Here Black should play 3…Bb4, which is the Nimzo-Indian Defence. A proper discussion of this opening is out of the scope of this article. White has a range of systems against the Nimzo (4 Qc2, 4 e3, 4 a3, 4 Nf3, 4 Bg5, 4 g3 and 4 Qb3 are the main ones) and Black has a range of replies against each.
White can also play 3 g3. In response, Black’s main options are 3…d5, 3…c5 and 3…Bb4+. I would suggest playing 3…d5, reaching the Catalan Opening, as in this move order White can force it in any case via 3 Nf3 d5 4 g3.
On move 2, White can play 2 Nf3, to which Black’s simplest reply is 2…d5. Then 3 c4 e6 transposes to the position after 1 d4 Nf6 2 c4 e6 3 Nf3 d5, while 3 e3 Bf5, 3 Bf4 c5 and 3 Bg5 Ne4 are all fine for Black.
White plays 1 c4
While the previous two move orders discussed allowed Black to sidestep the main variations of the English Opening, here Black doesn’t have this luxury.
The simplest approach is to play either 1…e5 or 1…c5, forcing play into independant English Opening lines. These are generally reliable, but out of the scope of this article.
It is also possible to play 1…Nf6, when 2 d4 transposes to the lines considered after 1 d4 Nf6 2 c4 above. However, Black is more likely to face one of 2 Nc3, 2 Nf3 or 2 g3, when White keeps his options open.
White plays 1 Nf3
Black can meet 1 Nf3 with 1…d5, when 2 d4 Nf6 transposes to the lines covered after 1 d4 Nf6 2 Nf3 d5, while 2 c4 e6 either transposes to the main lines after 3 d4 Nf6 or leads to a Reti.
Should White continue with 2 g3 or 2 b3, Black can develop solidly, looking to develop his bishop on f5 or g4. If White plays c4, play will lead to lines of the Reti Opening.