Key ideas
- 4...c5 hits d4 at once. After 5.Bd3 Nc6 6.Nf3 Bxc3+ 7.bxc3 d6, Black has the Hübner Variation: the doubled c-pawns are fixed by ...d6 and ...e5, and Black's knights play against White's bishops in a closed position.
- 5.Ne2 is the Rubinstein Variation proper. The knight avoids the pin and is ready to recapture on c3, so White can meet ...Bxc3 with Nxc3 and keep a healthy structure. After 5...cxd4 6.exd4 O-O 7.a3 the bishop has to decide.
- 4...O-O, the Normal Variation, keeps options open. After 5.Bd3 d5 6.Nf3 c5 7.O-O (the Gligoric System), 7...dxc4 8.Bxc4 cxd4 9.exd4 gives White an isolated queen's pawn, while other lines lead to hanging pawns or to the doubled c-pawns after ...Bxc3.
- Black can also fight for the light squares with 4...b6 and ...Bb7, or play 4...Nc6, the Taimanov Variation, aiming for ...e5.
Plans for White
Develop with Bd3, Nf3 or Ne2, and castle. If Black gives up the bishop, the bishop pair and the e3-e4 push are your long-term trumps; if not, a3 forces the question. In isolated-pawn positions, use d4 as a base for Ne5 and a kingside attack.
Plans for Black
Decide early whether to take on c3. In the Hübner, after ...Bxc3 close the centre with ...e5 and ...d6, keep White's bishops shut in and play against the doubled c-pawns. In the open lines, active development and pressure on d4 matter more than the bishop pair.
For the wider picture, see the Nimzo-Indian Defense guide.