The main line continues with 5.e3, when Black usually develops with 5... Nbd7; though a developing move, 5....Be7 is seldom seen nowadays, as players realised early on that at e7, the bishop was passively placed and does nothing to further one of Black's aims, the freeing move ....e5.
The main variation of the Semi-Slav is the Meran Variation, 5.e3 Nbd7 6.Bd3 dxc4 7.Bxc4 b5, (ECO codes D46 to D49), when play usually continues with 8.Bd3, with 8.Be2 and 8.Bb3 less common alternatives. The variation is named after the town of Meran (Merano) in northern Italy, after its successful use in the game Gruenfeld-Rubinstein during a tournament held in that city in 1924. Viswanathan Anand won two games with Black in his World Chess Championship 2008 match with Vladimir Kramnik. Black surrenders his outpost on d5, gaining a tempofor queenside space expansion by ...b7-b5. White will play in the centre, leading to a rich, complicated game. These opposing strategies, with the ensuing keen play, have long made the Meran a favourite for enterprising players of either color.
If White wants to avoid the Meran Variation without entering the muddy waters of the Anti-Meran, 5.cxd5 or 5.Qb3 are possibilities, though after 5....exd5, the former leads to a line of the QGD Exchange where White's Nf3 enables the Black QB to freely develop, which should give equality (ECO code D43 and D45). After 5.e3 Nbd7, the main alternative to 6.Bd3 has become 6.Qc2, waiting for Black to commit to ....dxc4 before playing Bd3. Once a sideline, this move exploded in popularity, in large part due to Anatoly Karpov's advocacy during the 1990s.
Shirov-Shabalov Gambit in Anti-Meran
Another increasingly common gambit line used in the Anti-Meran system varition is the sharp 5.e3 Nbd7 6.Qc2 Bd6 7.g4. Popularized by Alexander Shabalov and Alexey Shirov, the gambit destabilizes the center for Black and has been successful for several grandmasters, including Kasparov.
The Anti-Meran Gambit (ECO code D44) arises after 5.Bg5. White refuses to shut in the dark-squared bishop, instead developing it to an active square where it pins the black knight. It is now possible for Black to transpose to either the Cambridge Springs Defence with 5....Nbd7 6.e3 Qa5, or enter the Orthodox Defense with 6....Be7, though in practice he usually opts for either of the variations given below.
This line is extremely complicated, with theory stretching past move thirty in some variations. Black captures a pawn by 5...dxc4. White takes control of the centre with 6.e4 as Black defends his booty with 6...b5. The main line of the Botvinnik now continues with 7.e5 h6 8.Bh4 g5 9.Nxg5 hxg5 10.Bxg5 Nbd7. White will regain his piece with interest, emerging with an extra pawn ahead, but Black will soon complete his development, gaining great dynamic compensation, whereas White's task is rather more difficult. White will fianchetto his king's bishop andcastle kingside, while Black will play ...c5, ...Qb6, castle queenside, and can carry out an attack in the centre or on either flank, leading to complex play. The opening was introduced by Mikhail Botvinnik in the 1945 USSR vs USA radio match vs Arnold Denker. Today, Alex Yermolinsky has an excellent record with the White pieces and Alexei Shirov has been Black's chief proponent in this variation.
The Moscow Variation 5.Bg5 h6 6.Bxf6 Qxf6, gives rise to play of a different character than the lines after 5....dxc4. Black has the bishop pair, but must avoid prematurely opening the position in the face of White's superior development and central control. The gambit line 6.Bh4 (the Anti-Moscow Variation) was once considered dubious, but has seen a recent resurgence. In return for the pawn, White receives a lead in development and a strong initiative. This dynamic mode of play, which is characteristic of the modern game, has seen this line being played by many strong grandmasters, though the verdict on the line is unclear.
Alternatives after 5.e3 Nbd7 6.Bd3
Though appearing in contemporary master play with less frequency than the Meran, there are other playable moves: 6....Be7, 6....Bb4, introduced by the Italian master Max Romih, and 6....Bd6, which was much the most popular line before the debut of the Meran, and espoused by the American grandmaster Arthur Bisguier throughout his career.
After 6....Bd6, 7.0-0 0-0 8.e4 dxe4 9.Nxe4 Nxe4 10.Bxe4 is the most commom line line in practice. There are now several alternatives for Black, with one a clear error, as it loses a pawn: 10....e5 11.dxe5 Nxe5 12.Nxe5 Bxe5 13.Bxh7+ Kxh7 14.Qh5+ Kg8 15.Qxe5. This line, however, has a strong drawish tendency in practice, due to the opposite-coloured bishops, though all the heavy pieces remain on the board.
Black's other choices include 10....c5, though theory regards this as premature as it enables White to play for a kingside attack with 11.Bc2, followed by Qd3 and Bg5. 10....Nf6 has also been played, but this misplaces the knight, as it does nothing to further Black's play against the centre by means of either ....c5 or ....e5. 10....h6 is the move preferred by Bisguier and has come to be considered strongest.
The other ideas, 6....Be7, which has the same drawback as after 5.e3 Be7, and 6....Bb4, have become sidelines in modern play.