While 2…g6, 2…d6, 2…e6 and 2…b6 are all quite orthodox choices for Black after 1 Nf3 Nf6 2 c4, there are of course other possibilities. I shall be looking at the positions after 2…c5 in my series of posts on the Symmetrical English. The only other variation I think worthy of looking at in depth is 2…Nc6.
This system, nowadays referred to as the “The Black Knights’ Tango”, used to be either ignored or regarded as somewhat unorthodox. However, nowadays it has a respectable reputation below super GM level.
As the immediate point of the move is to support …e5, I would suggest following the usual policy after 1 Nf3 of preventing this by playing 3 d4.
Black’s recommended move is now 3…e6. This might at first sight seem odd, but Black’s idea is simple enough: he intends to play …Bb4+, leading either to a Nimzo-Indian after Nc3, or a Bogo-Indian after Bd2 or Nbd2. While Black is admittedly committed to a line with …Nc6, this is not necessarily a problem, especially in the Bogo-Indian, where such a move in conjunction with a later …d6 and …e5 can be effective in neutralising White’s advantage.
For this reason, the move that has always appealed to me is 4 a3.
In response to this, there are two basic Black systems: 4…g6 and 4…d5. I shall look at each of these in turn below.
Black plays 4…g6
This is very similar to the King’s Indian, but not quite the same, and White has to adopt a different formation to that employed against the King’s Indian proper.
To recap, the recommended approach against the King’s Indian is the line 1 Nf3 Nf6 2 c4 g6 3 Nc3 Bg7 4 e4 d6 5 d4 O-O 6 Be2 e5 7 O-O Nc6 8 d5 Ne7 9 b4. Naturally, other move orders are possible.
One important point in the above sequence is that Black cannot play …Nc6 before …e5, because then White plays d5, driving the knight either to e5 or b8, both of which are unsatisfactory. I am thinking of the lines 6…Nc6 7 d5 Ne5 and 6…Nc6 7 d5 Nb8.
In contrast, in the Black Knights’ Tango, after 1 Nf3 Nf6 2 c4 Nc6 3 d4 e6 4 a3 g6 5 Nc3 Bg7 6 e4 d6, Black has played an early e6, while White has only gained a3 in return. If White plays 7 Be2 O-O 8 O-O, then 8…e5 9 d4 Ne7 10 b4 would give him an improved version of the main line, since the extra a3 is pretty useful (e.g. against …a5). However, Black now has 8…Re8, because 9 d5 can be met by 9…Ne7, and the knight has been driven to a decent square; alternatively 9 Be3 e5 10 d5 Nd4! equalises (c.f. 8 Be3 Re8 9 d5 Nd4! in the King’s Indian proper).
White therefore needs to adopt an alternative system. Khalifman recommends adopting the following approach: 7 h3 0-0 8 Bg5. Now Black will usually break the pin with 8…h6, otherwise it could prove awkward. Then after 9 Be3 Re8 10 Bd3, the move 10…e5 is less effective, as after 11 d5, Black has to play 11…Ne7, as 11…Nd4 loses a pawn. Instead, 11…Ne7 12 g4, followed by Nh2-f1-g3, gives White a strong bind on the position.
Black plays 4…d5
By choosing 4…d5, Black argues that …Nc6 is better value for him than a3 is for White in a Queen’s Gambit type of position. However, I don’t really like the move …Nc6, blocking the c-pawn, in the Queen’s Gambit, except in some specific cases.
I would play the natural 5 Nc3 in this position. It is then difficult to decide what should be considered the “main line”, as Black’s whole set up seems unnatural and lacking a coherent theme.
The sharpest approach for Black is the pawn grab 5…dxc4. However, after the following line given by Khalifman, White regains the pawn with a space advantage, while Black only has the bishop pair for company: 6 e4 Na5 7 Bxc4 (a common tactic in such situations) 7…Nxc4 8 Qa4+ Bd7 9 Qxc4 Be7 10 0-0 0-0 11 Rd1.
Against a quieter move such as 5…Be7, White could continue with 6 Bg5 or 6 Bf4, arguing that …Nc6 is not a great move against either system. 6 Bf4 is especially attractive, as a3 is quite a normal move for White in the Queen’s Gambit Declined Bf4 system.