Classical Variation

The Classical Variation, also called the Capablanca Variation, is classified as E32. With 4. Qc2 the queen defends the c3-knight, so that ...Bxc3 can be answered by Qxc3. White then keeps the pawn structure intact and the bishop pair in hand. From c2 the queen also bears on e4, the square at the heart of the Nimzo struggle. The cost is time. The queen usually has to move again, and White's kingside pieces stay at home, so Black tends to open the position early to exploit the lead in development. The line was popular in the opening's early years and then lost ground to 4. e3. It returned in the 1990s and now rivals the Rubinstein in frequency.

Black has four main replies: 4...O-O, the most common; 4...c5, the Berlin Variation; 4...d5, the Noa Variation; and 4...Nc6, the Zurich Variation. The modern main line runs 4...O-O 5. a3 Bxc3+ 6. Qxc3 b6, the Keres Defense. After that, 7. Bg5 Bb7 and 7. Nf3 Bb7 8. e3 are both standard. Playing 6...b5 instead of 6...b6 gives the Vitolins-Adorjan Gambit. The engine rates the position after 4. Qc2 as balanced, and online results are close to even.