Normal Variation

With 2. c4 White adds a second pawn to the fight for d5 and takes queenside space. Because the c-pawn has already advanced, the queen's knight can later go to c3 without obstructing it. Black now chooses between two broad approaches: challenging the d4-c4 pair at once with pawns, or first freeing a bishop and leaving the center to be contested later. The position is one of the most frequently reached in the Lichess database. Results are close to level, and engines consider it roughly balanced, with 2...e6, 2...c6 and 2...g6 among their preferred replies.

The bishop-freeing moves form the main body of theory. Tartakower grouped setups with ...d6 and ...g6 as Old Indian defenses and those with ...e6 and ...b6 as Neo-Indian ones. 2...e6 opens the f8-a3 diagonal and stays flexible. It can head for the Nimzo-Indian, Queen's Indian, Bogo-Indian, Benoni or Catalan, or reach a Queen's Gambit Declined with a later ...d5. 2...g6, the West Indian Defense, prepares ...Bg7 and usually becomes a King's Indian, or a Grünfeld after 3. Nc3 d5. 2...d6, the Old Indian proper, can reach King's Indian positions via 3. Nc3 g6 4. e4 Bg7. It also has independent lines in which Black plays ...Nbd7, ...e5, ...Be7 and ...O-O. 2...b6, the Queen's Indian Accelerated, fianchettoes the queen's bishop without the usual ...e6 and Nf3.

The pawn challenges produce sharper, more unbalanced games. 2...c5 is the Benoni Defense. After 3. dxc5 e6 Black recovers the pawn comfortably, so White normally advances with 3. d5. Black then attacks the chain with 3...e6, the Modern Benoni, or offers a queenside pawn with 3...b5, the Benko Gambit. 2...e5, the Budapest Gambit, offers a pawn with tempo after 3. dxe5 Ng4. White generally returns it and keeps a small edge. 2...d5, the Marshall Defense, does not reach the Queen's Gambit Declined. After 3. cxd5 Nxd5 4. e4 Nf6 White has gained a broad center, and in the Lichess games White scores well against it.

The remaining replies are rarer. 2...c6, the Slav Indian, invites a Slav Defense, which White can accept with 3. Nc3 or 3. Nf3 or sidestep with 3. Bf4. 2...Nc6, the Mexican Defense, meets 3. d5 with 3...Ne5. Its main line is 3. Nf3 e6 4. Nc3 Bb4, where 3. Nf3 stops ...e5. 2...b5, the Pyrenees Gambit, tries to lure the c-pawn away from the center but is considered dubious. 2...g5, the Medusa Gambit, simply loses a pawn to 3. Bxg5 and is regarded as unsound.