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

White chooses to keep their bishop. They keep the pressure on Black's knight, and indirectly on the e5 pawn that it defends.

The key difference between this position and the position after 3. Bb5 is that now Black has the option of b5, whenever they like, which will cut off the threat of Bxc6 followed by Nxe5 for good. Black doesn't need to play ...b5 until White protects their e-pawn (see below) so usually concentrates on development first.

Black's main priority should be to develop their kingside and castle.

4...Nf6 is by far the most common continuation^[1] and most principled move. Black starts development of their kingside while also threatening the e4 pawn. This is just referred to as the mainline, rather than the Berlin defence deferred.

4...Bc5, the deferred Classical defence, develops the kingside and begins to pressure f2. Playing in this order allows Black to play d6 or to develop their kingside knight to e7 next, without blocking in the bishop.

4...d6, known as the Modern Steinitz, directly defends the pawn and seeks to end any danger of Nxe5. Black wants a quieter game, avoiding mainline Spanish theory. It opens the way for the queenside bishop to develop to d7, interposing the pin, or to g4, but the kingside bishop will now have a harder time reaching its potential.

Although it self-pins Black's knight, the addition of a6 Ba4 makes this less dangerous: the response 5. d4 is less critical of this line than of the Old Steinitz (3...d6) because Black can respond 5...b5 6. Bb2 Nxd4.

4...b5 straight away is called the Caro variation.

...b5 ends White's bishop's pressure on the Black's knight and its indirect pressure on e5. This would end White's threat to win the e-pawn and Black usually ends up playing it at some point.

It is not typical to play it straight away on move four however, because White isn't actually threatening to win the pawn yet. Black still has the tactic Qd4!: Bxc6 dxc6 Nxe5 Qd4! forks White's knight and e4 pawn. Black would get the pawn back and the bishop pair to boot. Therefore there is no immediate need to cash in ...b5 until White protects their e4 pawn, disarming the Qd4 tactic (see diagrams below), and there is no need for Black to give White the tempo to move their bishop onto the more dangerous b3-f7 diagonal.

4...b5 is more common at the club-level where it is normally just a move order difference, with the intention of transposing back into a mainline Spanish after 5. Bb2 Nf6. However, this move order is inaccurate because, instead of transposing, White has additional options. The most critical move is 6. d4. Black needed to have developed their kingside more before allowing White pressure on f7.

Alternatively, 4...b5 5. Bb2 may lead to several lines with their own character:

• 5...Na5, the Norwegian variation. Black is determined to eliminate White's bishop and get the bishop pair. This is the most reputable continuation after and is the usual plan after 4...b5 in master-level games.
• 5...g6 has been tried, most successfully by Shakhriyar Mamedyarov with Black in a blitz match against Vladimir Kramnik.^[2]
• 5...Bc5 resembles the Classical defence but is called the Graz variation.

Black has the option for several sidelines that are similar to the options they had on their previous move. After 3...a6 4. Ba4, most are now known as "deferred" defences.

• 4...f5 is the deferred Schliemann. This unusual line was used as a surprise weapon by Praggnanandhaa in the 2024 Candidates.^[3]
• 4...g6 is the deferred fianchetto defence.
• 4...Nge7 is the deferred Cozio.
• 4...Nd4 is the deferred Bird.

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

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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.