Semi-Slav Defense
The Semi-Slav Defense is a variation of the Queen's Gambit Declined chess opening defined by the position reached after the moves:
The position may readily be reached by a number of different. Black's supporting pawns resemble a mixture of the Orthodox Queen's Gambit Declined, e6, and the Slav Defense, c6.
Black is threatening to capture the white pawn on c4 and hold it with...b7–b5. White can avoid this in a number of ways. About 80% of games continue 5.Bg5 or 5.e3: the former constitutes a sharp pawn sacrifice, while the latter restricts the dark-squared bishop from its natural to g5. Other possible moves are 5.Qb3, 5.g3 and 5.cxd5, the last of which, after 5...exd5, leads to a line of the QGD Exchange Variation where White's early Nf3 enables Black's queen bishop to freely develop, which should give equality. 5.Bf4 is considered somewhat inaccurate, as 5...dxc4 is favorable for Black.
The Semi-Slav is designated by codes D43 through D49 in Encyclopaedia of Chess Openings.
First moves and possible deviations
It is possible to reach the Semi-Slav through many move orders. White may start the game with either 1.d4, 1.Nf3 or even 1.c4, keeping the possibility of a Semi-Slav open. Black can choose different combinations of...d5,...c6,...e6 and...Nf6 as well in order to avoid certain variations or to open up some new opportunities of his own. This chapter looks at the first moves of the game from Black's point of view, assuming that he would prefer to play the Semi-Slav.1.d4 d5 move order
If White opens the game with 1.d4, Black is happy to respond with 1...d5 when aiming for a Semi-Slav. Of course White can continue the game with 2.Bf4 or even 2.Bg5, and the game will take a completely different path. In vast majority of master games, however, White players choose to play either 2.c4 or 2.Nf3. After 2.Nf3, the natural continuation for Black is 2...Nf6. Playing 2...c6 or 2...e6 might be somewhat inaccurate, since White always has the option of avoiding c2–c4, so developing the knight first makes a lot of sense.If White chooses the most common 2.c4, Black has three practical choices: either protect the pawn on d5 by playing e6 or c6, or alternatively capture the white pawn with dxc4. The first thing for Black players to consider is, what if White captures on d5 anyhow with cxd5. If Black has played the Slav move order, then after the recapture cxd5 the pawn structure is symmetrical. Should Black have played 2...e6 instead, the recapture exd5 leads to an imbalanced pawn structure called the Carlsbad structure, which might offer White some opportunities for a minority attack on the.
Slav move order: 2...c6
Protecting the d5-pawn with the c-pawn has at least three implications for Black. First, it allows Black to keep the option to enter the Slav Defense, i.e., developing his light-squared bishop to f5 at the appropriate moment, before moving his e-pawn. Second, it may discourage White from capturing on d5, given the somewhat drawish reputation of the Exchange Slav. Third, it prevents White from entering the Catalan opening with 3.g3.One drawback of playing 2...c6 is that White may continue 3.Nf3, and after 3...Nf6 play 4.e3, and now Black cannot really play the Semi-Slav since 4...e6 is considered to be good for White as he has not committed to Nc3 thus having other options to develop, for example Nbd2 or b3.
Queen's Gambit declined move order: 2...e6
Protecting the d5-pawn with the e-pawn allows Black to develop his more rapidly, but it does block the light-squared bishop for the time being. After 3.Nf3 Nf6 White has the option of entering the Catalan opening with 4.g3.If White continues 3.Nc3, Black has two options to proceed with a Semi-Slav in mind. First, Black can play 3...c6. Second, Black can play 3...Nf6, which gives White the opportunity to continue 4.cxd5 exd5 followed by 5.Bg5.
The triangle setup
After the move order 1.d4 d5 2.c4 c6 3.Nc3 Black has the opportunity to respond with 3...e6 instead of 3...Nf6. This "triangle setup" opens up some new alternatives for both players on the fourth move.Marshall Gambit
First, White has the opportunity to enter the Marshall Gambit by playing 4.e4. Play continues 4...dxe4 5.Nxe4 Bb4+. Now White has two alternative paths to continue. The main line is considered to be 6.Bd2 Qxd4 7.Bxb4 Qxe4+ and then White blocks the check with either his knight or bishop. Alternatively White can continue with 6.Nc3, and play continues 6...c5 7.a3 Ba5.Noteboom Variation
Second, if White continues 4.Nf3, Black has the extra option of playing 4...dxc4 entering the Noteboom Variation, named after Daniël Noteboom. If White wants to avoid this variation, he must play either 4.e4 or 4.e3. White now has a number of possible continuations, including 5.a4, 5.e3, 5.e4, or even 5.Bg5. A typical line in the Noteboom Variation continues: 5.a4 Bb4 6.e3 b5 7.Bd2 a5 8.axb5 Bxc3 9.Bxc3 cxb5 10.b3 Bb7 11.bxc4 b4 12.Bb2 Nf6 13.Bd3 Nbd7 14.0-0 0-0 with an interesting position where Black has two connected passed pawns on the queenside, while White has the bishop pair and dominates the center of the board.The "triangle setup" is not ideal for Black if White plays 3.Nf3 instead of 3.Nc3. Should Black play 3...e6 nevertheless, White has the option of continuing with 4.e3 or 4.Qc2, for example, thus avoiding the Noteboom Variation.
1.d4 Nf6 2.c4 e6 move order
Black has the option of delaying the move...d7–d5, for instance to avoid the exchange cxd5. If White continues 3.Nc3, Black has the option of transposing to a Nimzo-Indian with 3...Bb4. Should White choose to play 3.Nf3 instead, Black can simply play 3...d5, and then after 4.Nc3 c6 we are back at the start of the Semi-Slav. This move order, however, allows White to play the Catalan Opening with either 3.g3, or alternatively 3.Nf3 d5 4.g3.Semi-Slav: 5.e3 variations
Roughly 50% of the games continue with 5.e3. White gives priority to developing his light-squared bishop, and accepts that for the time being the dark-squared bishop will remain somewhat out of play. The main line continues with 5...Nbd7. 5...Be7 is rare, as the bishop is passively placed on e7 and does not support the freeing move...e5. The unusual move 5...a6 is considered solid for Black. Some sources call 5...a6 the "accelerated Meran".Meran Variation: 6.Bd3
One of the main variations of the Semi-Slav is the Meran Variation. White plays 6.Bd3, provoking the continuation 6...dxc4 7.Bxc4 b5 where black surrenders his center in exchange for queenside expansion and some tempo against the white bishop. The line was first played in 1906 in the game Schlechter–Perlis. The variation takes its name from the town of Meran in northern Italy. During a 1924 tournament in Meran, it was used successfully in the game Gruenfeld–Rubinstein. Gruenfeld adopted the same variation two rounds later against Spielmann, winning as well. White will play in the center, leading to a rich, complicated game. These opposing strategies, with the ensuing keen play, have long made the Meran a favorite for enterprising players of either color. An example is Gligoric–Ljubojevic, Belgrade 1979.Though appearing in contemporary master play with less frequency than the Meran, there are other possibilities: 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 the main line 6.Bd3 dxc4 7.Bxc4 b5 White has three alternative retreats for the bishop. The vast majority of games continue 8.Bd3, but the moves 8.Bb3 and 8.Be2 are also possible.