Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...Bc5/4. O-O

White castles.

By activating the rook, White renews the threat to win Black's e-pawn, because if e.g. 4...a6 5. Bxc6 dxc6 6. Nxe5, the 6...Qd4 tactic is no longer a threat. If 6...Qd4?, the rook on f1 prevents 7...Qxf2?? from resulting in checkmate, and the apparent fork of the knight and e4 pawn is diffused by 7. Nf3 Qxe4?? 8. Re1! pinning Black's queen on the now open e-file.

4...Nd4 is a common continuation, threatening the Spanish bishop. This is similar to the Bird defence (3...Nd4) but now Black has the option of recapturing with the bishop instead of the pawn: 5. Nxd4 Bxd4. This allows White to get in 6. c3 with tempo, however.

4...Nf6 transposes into the Beverwijk variation of the Berlin defence. This counterattacks e4, so that in the event White chooses Bxc6 dxc6 Nxe5, it is at best a trade of pawns.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.