4.c3 is the classical reply and supports the central advance 5.d4. The main reply is 4...Nf6, which was first analyzed by
Greco in the 17th century. After 5.d4, Black usually responds with 5...exd4. From here, 6.cxd4 is the classical continuation, to which Black almost always responds with 6...Bb4+ (6...Bb6 is weak because of 7.e5). White can then play 7.Nc3, 7.Bd2, 7.Nbd2, blocking the check, or 7.Kf1, which avoids
pinning a piece to the king at the cost of losing castling rights. The move 6.e5, advocated by
Evgeny Sveshnikov, is White's primary sixth move alternative, and has become more popular than 6.cxd4, though it was once rare. 6.b4, advocated by
Daniil Dubov and others, is also seen, as well as 6.0-0. White may combine other fifth moves with 4.c3 instead of playing 5.d4. 5.d3 transposes to the
Giuoco Pianissimo, a move which became more common than the traditional 5.d4 in the 20th century. 5.0-0 enters the
Albin Gambit, which can be accepted with 5...Nxe4 or declined, usually with 5...d6. Black also has fourth move alternatives in response to 4.c3. The most notable are 4...Qe7, the
Closed Variation, and 4...d6, typically leading to the La Bourdonnais Variation after 5.d4 exd4 6.cxd4 Bb6.
Old main line: 6.cxd4 Bb4+ 7.Nc3 Nxe4 8.0-0 7.Nc3 offers a pawn
sacrifice. It usually continues 7...Nxe4 8.0-0. After this, Black usually plays 8...Bxc3. White can then play 9.d5, the Møller Attack, sacrificing a pawn for development and the initiative, or simply recapture with 9.bxc3, which was the most common move before the discovery of 9.d5, but is now a side line. 8...Nxc3, which was played in Greco's games (as White) in this line, is a notable alternative for Black. Black sometimes also avoids the sharp complications of the Møller Attack after 7.Nc3 with 7...d5 (which was played several times against
Wilhelm Steinitz), 7...d6?!, 7...0-0 or 7...Bxc3, but these lead to passive positions for Black.
Møller Attack: 8...Bxc3 9.d5 {{Chess diagram small After 8...Bxc3, 9.d5 is the most common move for White. The most common continuation is 9...Bf6 (followed by 9...Ne5), with the main line continuing 10.Re1 Ne7 11.Rxe4 d6 12.Bg5 Bxg5 13.Nxg5 h6; 13...0-0 14.Nxh7! has been analyzed to a draw with best play, although Black has many opportunities to go wrong. After 13...h6!, the most common continuation is 14.Qe2, where after 14...hxg5 15.Re1 Be6! 16.dxe6 (White also can try 16.Qd2 c6! 17.dxe6 f6 18.Bd3 d5 19.Rg4 Qc7 20.h3 0-0-0 21.b4, attacking) 16...f6 17.Re3 c6 18.Rh3 Rxh3 19.gxh3 g6 it is doubtful that White has sufficient
compensation for the sacrificed pawn, according to
Larry Kaufman; 14.Qh5 0-0 15.Rae1 Ng6! (or 15...Nf5!) also favors Black, as does 14.Bb5+ Bd7. A recent try for White is 12.Rf4, with the idea of sacrificing
the exchange on f6 for attacking chances, as seen in the game
Jorden van Foreest–
Levon Aronian, Chessable Masters 2021. It has the advantage that it has not been analyzed as deeply as the traditional 12.Bg5. Black has the option, however, of inviting a repetition with 12...Ng6 13.Re4+ Ne7, as occurred in
Rauf Mamedov–
Sergey Karjakin, Gashimov Memorial, Baku 2021. If instead Black plays 13...Be7, White has 14.h4! with good practical chances. The pawn thrust 12.g4 is another line occasionally seen for White. Black has the ninth move alternative of 9...Ne5, with the most common continuation being 10.bxc3 (10.Qe2 is also common) Nxc4 11.Qd4, followed by 11...0-0 12.Qxe4 (or 12.Qxc4) or 11...f5 12.Qxc4 d6. 11...Ncd6?! is inferior due to 12.Qxg7 Qf6 13.Qxf6 Nxf6 14.Rfe1+ Nfe4! (both 14...Kf8 and 14...Kd8 lose) 15.Nd2 f5 16.f3 and White has the better chances in the coming endgame.
Greco's line: 8...Nxc3 9.bxc3 {{Chess diagram small {{Chess diagram small After 8...Nxc3, 9.bxc3 is White's usual reply. The line is but inferior to allowing the Møller Attack. If 9...Bxc3?! 10.Qb3 Bxa1?, White wins with 11.Bxf7+ Kf8 12.Bg5. Greco's game (probably analysis) continues 12...Ne7 13.Ne5 (13.Re1 and 13.Rxa1 also win) 13...d5 14.Qf3 Bf5 15.Be6 g6 16.Bh6+ Ke8 17.Bf7. This
trap is well known, and Black can avoid it by playing 10...d5. For this reason, the Scottish master
James Aitken proposed 10.Ba3, which gives White the advantage. After 9.bxc3, instead best for Black is 9...d5!. A typical continuation is 10.cxb4 dxc4 11.Re1+ Ne7 12.Qa4+! Bd7 13.b5 0-0 14.Qxc4 Ng6!.
White's seventh move alternatives 7.Bd2 If White does not want to gambit , 7.Bd2 is a good alternative. A possible continuation is 7...Bxd2+ 8.Nbxd2 d5 9.exd5 Nxd5 10.Qb3 Nce7 (10...Na5 is an alternative, inviting a repetition of moves after 11.Qa4+ Nc6 [threatening 12...Nb6] 12.Qb3 Na5) 11.0-0 0-0 12.Rfe1 c6. In this position White has more freedom, but the
isolated d-pawn can be a weakness. Another possible continuation, recommended by Kaufman, is 7...Nxe4 8.Bxb4 Nxb4 9.Bxf7+ Kxf7 10.Qb3+ d5!? (10...Kf8 11.Qxb4+ Qe7 12.Qxe7+ Kxe7 is safer, reaching an
endgame) 11.Ne5+ Ke6! 12.Qxb4 c5!?, but this line is significantly less common.
7.Nbd2 7.Nbd2 is also a viable move for White, although this still only offers approximate equality.
Kraków Variation: 7.Kf1 7.Kf1 was named the
Kraków Variation after members of the Kraków Chess Club ran a and published analysis of it in 1909. It has the obvious disadvantage of giving up castling rights, thereby impeding the entry of the king's rook into active play, but avoids self-pinning. It was occasionally seen in the 19th and early 20th centuries but is now largely abandoned. It most often continues with either 7...d5 8.exd5 Nxd5 9.Nc3 or 7...Nxe4 8.d5 Ne7 9.Qd4 Nf6 10.Bg5.
6.e5 {{Chess diagram small {{Chess diagram small White can also try 6.e5, a line favored by
Evgeny Sveshnikov which has seen a surge in popularity in the early 21st century. Black's only good reply is 6...d5, immediately striking back in the . Alternatives are weak: • If 6...Ng4, White may try the temporary sacrifice 7.Bxf7+ Kxf7 8.Ng5+, but the simpler 7.cxd4 is clearly better for White. Black's knight is badly placed and White dominates the center. • If 6...Ne4, 7.Bd5! traps the knight and forces Black to choose between the weakening 7...f5 and the speculative sacrifice 7...Nxf2!? The latter line led to a famous win for Black in the game known as "Petrov's Immortal", Hoffmann–
Petrov, Warsaw 1844: 8.Kxf2 dxc3+ 9.Kg3 cxb2 10.Bxb2 Ne7 11.Ng5? Nxd5 12.Nxf7 0-0 13.Nxd8 Bf2+ 14.Kh3 d6+ 15.e6 Nf4+ 16.Kg4 Nxe6 17.Nxe6 Bxe6+ 18.Kg5 Rf5+ 19.Kg4 h5+ 20.Kh3 Rf3#. Instead of the aggressive 11.Ng5?, White should consolidate with 11.Qc2 or 11.h3, with the better chances in each case. After 6...d5 7.Bb5 Ne4 8.cxd4, 8...Bb6 is approximately equal. 8...Bb4+, the Anderssen Variation, typically continuing 9.Bd2 Nxd2 10.Nbxd2 0-0, is considered less accurate. After 8...Bb6, the main line continues 9.Nc3 0-0 10.Be3 Bg4 (10...f5 is also common) 11.h3 Bh5 12.Qc2, and from there 12...Bg6 13.Qb3 Ne7 14.0-0 c6 15.Bd3, 12...Nxc3 13.bxc3 f6 or 12...Ba5 13.0-0 Bxf3 14.gxf3. White has a advantage; Black has a powerful knight. == Closed Variation: 4.c3 Qe7 ==