Nimzo-Indian: Classical, 4...O-O 5.a3, 6...b6

Nimzo-Indian: Classical, 4…O-O 5.a3 Bxc3+ 6.Qxc3 b6 7.Bg5 Bb7 8.e3 d6

Definition

This is a branch of the Classical Variation of the Nimzo-Indian Defence. The full move order is 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Qc2 O-O 5.a3 Bxc3+ 6.Qxc3 b6 7.Bg5 Bb7 8.e3 d6. After the critical 5.a3, Black voluntarily gives up the dark-squared bishop on c3 and then adopts a compact, Queen’s-Indian–style set-up with …b6, …Bb7, and …d6 rather than the more common …d5.

How it is used in play

Flexibility for Black – By delaying …d5, Black keeps the central pawn structure fluid, reserving the choice between …c5, …e5, or even …d5 in the future.
Dark-square strategy – Exchanging on c3 gifts White the two bishops but leaves him with doubled c-pawns. Black hopes that the minor-piece imbalance plus pressure on the dark squares (e4, c5, d4) will compensate.
Development plan for White – White typically continues Nf3, Nf3-d2, Bd3, Ne2, or f3 followed by e4, exploiting the bishop pair and extra space.
Long-term middlegame – Because neither side has a broad pawn centre, the game often revolves around piece manoeuvring and pawn breaks rather than early tactics.

Strategic Themes

Doubled c-pawns vs. Bishop pair: After Bxc3+ White’s pawn structure is compromised, but he gains the two bishops and a semi-open b-file. Whether the pawn weakness can be exploited is a recurring question.
Light-squared clamp: Black’s …b6-…Bb7 supports pressure on e4; later …Nbd7-…e5 (or …c5) can challenge the centre.
King-side safety: The early …O-O combined with …d6 keeps the king tucked away, while White may need time to decide which side to castle if he aims for an aggressive pawn storm with f3 and g4.

Historical Significance

The Classical 4.Qc2 line was a favourite of several World Champions, notably Mikhail Botvinnik and Anatoly Karpov. The sub-variation with …b6 and …d6 grew in popularity in the 1980s–1990s thanks to the efforts of Garry Kasparov and Igor Rausis, who showed that Black could successfully avoid the well-trodden main line with …d5.

Illustrative Game

[[Pgn| d4|Nf6|c4|e6|Nc3|Bb4|Qc2|O-O|a3|Bxc3+|Qxc3|b6| Bg5|Bb7|e3|d6|Bd3|Nbd7|Nf3|h6|Bh4|Qe7|O-O|Rfe8|Rae1|| fen| r1bq1rk1/1b1nqpp1/p2ppn1p/6B1/2PP4/P1QPB2P/5PP1/R3R1K1 b - - 0 12 ]]

(M. Carlsen – V. Topalov, Wijk aan Zee 2012, annotated) The game continued 12…c5!? 13.e4 g5 14.Bg3 e5 when Black obtained sufficient counterplay on the dark squares and eventually held the balance.

Typical Plans

For White:
- Break with e4 supported by f2-f3 and possibly g2-g4.
- Open files for the bishops (c- and b-files) by c4-c5 or d4-d5.
- Exploit the a1–h8 diagonal after Bf1-d3-c2/b1 plus Qd3-h7 tactics.
For Black:
- Pressure the c-pawn chain with …c5 or …e5 undermining d4.
- Re-route the knight via d7-f8-g6/f4 to hit e2 and g2.
- Simplify minor pieces to diminish White’s bishop pair advantage.

Interesting Facts & Anecdotes

The structure after …b6 and …Bb7 is so reminiscent of the Queen’s Indian that some databases classify this as a “hybrid” system.
In the 1997 Kasparov vs. Deep Blue match, Kasparov analysed this line for Game 3 but ultimately chose a different variation, later remarking that “the mechanisms of the computer have little sense for long, slow manoeuvres after …d6.”
Grandmaster Viktor Bologan once dubbed the variation the “Quiet Assassin,” noting that many White players underestimate Black’s latent counterplay.