Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...d6

Much of the play and counterplay in the beginning of the Spanish opening revolves around White creating threats to play Nxe5, Black defending against them, and White finding new ways to reinvigorate the threat. By defending e5 with a pawn, 4...d6 defuses the threat for good.

4...d6 has the advantage of defending e5 and allowing Black's queen's bishop to develop, but closes off the diagonal Black opened for the king's bishop when they played 1...e5, and transforms White's bishop's latent pressure on their knight into a pin. The "modern Steinitz" or "deferred Steinitz" defence is a strict improvement over Steinitz's original suggestion or the "Old Steinitz", 3...d6, because the inclusion of 3...a6 4. Ba4 means Black can cut off that pin whenever they wish with ...b5.

The difference can be seen if White tries 5. d4?!.

5. d4?! on the face of it seems reasonable, for the same reasons it is the critical move against the 3...d6 move order. Black has only one defender of e5 (...d6 added the pawn to the defence but remove the knight by pinning it). So, White hopes to win it by playing dxe5 dxe5 Nxe5. If this compels Black to take on d4 instead, White thinks, then 5...exd4? 6. Nxd4 threatens Nxc6 bxc6 Bxc6+ to win a pawn and an exchange.

But White reckons without the intermezzo 5...b5! 6. Bb3 and now the knight is unpinned^[1] and attacks the centre. 6...Nxd4 7. Nxd4 exd4 and White may have calculated that they win the pawn at the end of the line, but 8. Qxd4?? stumbles into the Noah's Ark Trap: White's bishop on b3 is low on squares. If Black could catapult their pawn to c4, they would trap it, and White's queen on d4 now gives Black a way to get their pawn to c4 with tempo. The full line, including White's death throes, is 8...c5 9. Qd5 (threatens Qxf7#) Be6 (if 9...c4?? 10. Qxa8) 10. Qc6+ Bd7 11. Qd5 c4-+.

5. c3, it turns out, is an important move for White to include as it prepares d4 and also gives their bishop the c2 square to retreat to. This usually played either now or after castling and either order usually transposes: 5. c3 Bd7 6. d4 g6 7. O-O Bg7, or 5. O-O Bd7 6. c3 g6 7. O-O Bg7. Black's priorities are usually to unpin their knight (5...Bd7) and improve their unhappy king's bishop (...g6 & ...Bg7), but there are number of transpositions they may try, as ...d6 usually comes at some point in the other defences too. One sideline of note is 5. c3 f5, the Siesta variation.

5. Bxc6, a sort of delayed exchange variation, is an interesting alternative for White. This is not so unprincipled: while White lost a tempo playing 4. Ba4 then 5. Bxc6, all Black managed to get out of it was the move ...d6, which wasn't a developing move. By waiting until after Black has played ...d6 to trade pieces, White forces them to take back with the b-pawn, 5...bxc6, which is less freeing than ...dxc6 would have been. Now White may play 6. d4 and if 6...exd4 7. Qxd4. Black has nothing developed and doesn't have the option of ...Nc6 to develop with tempo on the queen.

Wilhelm Steinitz recommended 3...d6 against the Ruy Lopez in his 1889 book,^[2] and he relied on it during his 1894 match series with Emanuel Lasker, which he lost.^[3] 3...d6 is now known to be inferior. The inclusion of 3...a6 (which Steinitz had objected to on principle) 4. Ba4 significantly reinvigorates the defence. By the time he faced Lasker again in 1895, Steinitz had adopted this move order instead.^[4]

Though his book didn't specifically recommend all of them, several lines with the early ...d6 idea are named for Steinitz. Depending on your opening book, 3...d6 is the Steinitz and 3...a6 4. Ba4 d6 is the deferred Steinitz, or they're called the old Steinitz defence and the modern Steinitz respectively. Lichess's and 365Chess's opening books reserve "Steinitz deferred" for 3...a6 4. Ba4 Nf6 5. O-O d6.

Today it is a much more minor sideline behind 4...Nf6, but is seen occasionally at high levels in faster formats as a less theoretical, surprise option.^[5]

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 d6

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Wikipedia has related information at Ruy Lopez.

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