Chess Opening Theory/1. e4/1...c5/2. Nf3

Sicilian defence B27-B99 Sicilian Defence 2. Nf3 White increases their control of the d4 square: the conventional plan is to follow with 3. d4 cxd4 4. Nxd4 and open the position. Black's attention must now turn to their development: determining how to release their bishops, or first developing their knight. The main lines are 2...d6, accounting for almost half of games, and 2...Nc6 and 2...e6, each about half as popular as 2...d6. Release a bishop At some point Black would like to do something with their bishops, and that requires they make a pawn move first. 2...d6 is the main line. This releases the queen's bishop on the c8-h3 diagonal, and because of the pawn on d6, it usually means the king's bishop must fianchetto to g7. 2...d6 also controls e5, ensuring Black can play ...Nf6. After 3. d4 cxd4 4. Nxd4 this usually leads to the Najdorf, Dragon, classical, or Scheveningen Sicilians. A sideline is 3. Bb5+, the Moscow variation. 2...e6, sometimes called the French Sicilian, opens the a3-f8 diagonal for the king's bishop, and since the e6 pawn obstructs the queen's bishop, in these lines it is usually fianchettoed to b7. The typical ...e6 Sicilians are the Kan, Taimanov, or Four Knights variations. This can also transpose to the Scheveningen with ...d6. Preparing to fianchetto straight away is less common. 2...g6, preparing ...Bg7, is the hyper-accelerated dragon Sicilian (accelerated over the regular dragon Sicilian in that Black hasn't played ...d6 yet, and hyper-accelerated in that Black hasn't played ...Nc6 yet either). 2...b6!? to prepare Bb7, called the Katalimov, is non-standard. It may transpose into a Kan or other ...e6 Sicilian, though Black will have lost a tempo if they intend to play ...a6 and ...b5. Develop a knight 2...Nc6 is the most traditional move, sometimes called the old Sicilian. Black develops the knight to its natural square. It reserves options in the centre and keeps an eye on d4. After 3. d4 cxd4 4. Nxd4 this usually leads to the Sveshinkov, Accelerated Dragon or Kalashnikov Sicilians. However, this allows White to enter the sideline 3. Bb5, the Rossolimo attack. The most significant departure from the above main lines is 2...Nf6, the Nimzowitsch variation. As in Alekhine's defence, Black attacks the e-pawn to tempt it forward. Rare move orders 2...a6 is the O'Kelly variation. ...a6 is played in many Open Sicilian lines eventually to control the b6 square. This move order creates some novel possibilities, e.g. after 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 e5! White's knight cannot go to b5, so must retreat, and as Black hasn't played ...d6 yet (as in the Najdorf) they can play ...Bb4!. It can restrain some of White's longer-term plans and provide the springboard for ...b5. Another move-order anomaly is 2...Qc7 the Quinetros variation. Black's queen ends up on c7 in many Sicilians and this can transpose, e.g. 3. d4 cxd4 4. Nxd4 a6 5. Nc3 e6 transposes to the Kan Sicilian. 2...h6? is the Bücker variation. Black gives up another tempo. Is ...h6 a waste of time? It controls g5, so one idea is to reach a position like the Sveshnikov while preventing Bg5: 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 e5 6. Ndb5 d6. Bad moves 2...e5? is the Jalalabad variation where Black immediately throws away their e-pawn. 2...b5? is the Polish gambit. Black gives up their b-pawn to 3. Bxb5. 2...f5? is the Brussels gambit. Theory table 1. e4 c5 2. Nf3 2 3 4 5 Open Sicilian with 2...d6 ...d6 d4cxd4 Nxd4Nf6 Nc3a6 +/= Open Sicilian with 2...e6 ...e6 d4cxd4 Nxd4a6 Bd3Nf6 +/= Open Sicilian with 2...Nc6 ...Nc6 d4cxd4 Nxd4Nf6 Nc3e5 = O'Kelly Variation ...a6 c3d5 exd5Qxd5 d4e6 +/= Hyper-Accelerated Dragon ...g6 d4cxd4 Qxd4Nf6 Bb5Nc6 = Nimzowitsch Variation ...Nf6 e5Nd5 Nc3e6 Nxd5exd5 +/- Katalimov Variation ...b6 d4cxd4 Nxd4Bb7 Nc3d6 +/- Sicilian Defence References fi:Shakkiaapinen/Peli/1. e4/1...c5/2. Rf3