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Two Knights Defense

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h
Moves	1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6
ECO	C55–C59
Origin	Late 16th century
Parent	Italian Game
Synonym	Prussian Defense[1]

The Two Knights Defense (also called the Prussian Defense) is a chess opening that begins with the moves:

1. e4 e5

2. Nf3 Nc6

3. Bc4 Nf6

First recorded by Giulio Cesare Polerio (c. 1550 – c. 1610) in c. 1580,^[2][3] this line of the Italian Game was extensively developed in the 19th century.^{[citation needed]} Black's third move, attacking White's pawn on e4, is a more aggressive continuation than the Giuoco Piano with 3...Bc5. White’s most direct approach is 4.Ng5, immediately attacking Black’s vulnerable f7-pawn. David Bronstein noted that the term defense doesn’t capture the opening’s true character and suggested Chigorin Counterattack as a more accurate name.^[4] The Two Knights Defense has been played and analyzed by many aggressive players including Mikhail Chigorin, Paul Keres, and world champions Mikhail Tal and Boris Spassky.

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Knight Attack: 4.Ng5

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Classical line: 4.Ng5 d5 5.exd5 Na5

The move 4.Ng5 attacks Black's pawn on f7 in combination with White's bishop on c4. Once the most common move, such as during the era of Romantic chess, the move attracted criticism from players of the Classical school who argued that it violates opening principles because it moves a piece twice and attacks before development is complete. The leading German master of the early 20th century, Siegbert Tarrasch, famously called 4.Ng5 "a duffer's move" (ein richtiger Stümperzug),^[5] also translated as "a typical example of a bungling move" in the English translation of The Game of Chess.^[6] 4.Ng5 experienced a revival in popularity in the late 20th century, however, being adopted in the 1990s by Alexander Morozevich and Nigel Short,^[7] though it remains less common than 4.d3. It has been employed by world champions Wilhelm Steinitz, Bobby Fischer, Anatoly Karpov, Garry Kasparov, and Viswanathan Anand.

The only good defense for Black is 4...d5, blocking White's bishop's line of attack. After 4...d5, 5.exd5 practically wins a pawn by force, although Black gains compensation with quick development and initiative. The standard reply is 5...Na5, attacking the bishop before White can move the pawn and resume the attack. Notable alternatives are 5...Nd4 (Fritz Variation) and 5...b5 (Ulvestad Variation), which usually transpose into each other. The reply 5...Nxd5?! is considered too risky to play at the board, although it has not been definitively refuted. Black can also ignore the threat to f7 on the fourth move, most notably with 4...Bc5!?, the Traxler Counterattack, which leads to wild complications; in general, the 4.Ng5 variation is known for extensive theoretical analysis and sharp tactical play.

After 4...d5 5.exd5 Na5, the main line continues 6.Bb5+ c6 7.dxc6 bxc6, after which 8.Bd3 (modern line), 8.Be2 h6 9.Nf3 (traditional line), 8.Be2 h6 9.Nh3 (Steinitz Variation), and 8.Qf3 (Bogoljubow Variation) are all common continuations. 7...Nxc6 and 8.Ba4 are notable mistakes. 8.Be2 was the main line of the 4.Ng5 variation until the 21st century, but 8.Bd3 is now slightly more common than 8.Be2 and 8.Qf3 combined. There are also two notable sidelines. 6...Bd7 is a possibility for Black;^[8] it avoids the extensive theory of 6.Bb5+ c6 lines. 6.d3, the Kieseritzky Variation, similarly allows White to avoid the theory.

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Modern line: 7.dxc6 bxc6 8.Bd3

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Knight sacrifice line: 8.Bd3 Nd5 9.Nf3 Bd6 10.0-0 0-0 11.Re1 f5 12.Nxe5 Qf6 13.Nf3 g5 14.c4 Nf4 15.Bf1 g4 16.d4 gxf3 17.Qxf3 Ne6

This move was still considered a mistake by Jan Pinski in 2004^[7] but is now the main line of the 4.Ng5 variation. The line has some continuations involving White sacrificing a knight for two more pawns, leaving material equal given the pawn captured on the fifth move.

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Traditional line: 6.Bb5+ c6 7.dxc6 bxc6 8.Be2 h6 9.Nf3 e4 10.Ne5

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Knorre Variation: 10...Bd6 11.d4 Qc7 12.Bd2

9.Nf3 almost always continues 9...e4 10.Ne5, leading to a position where White is behind in development but has an extra pawn as well as a better pawn structure; Black has two isolated pawns. This line was the most common continuation of the 4.Ng5 variation in the 19th and 20th centuries, but has been surpassed in popularity by 8.Bd3 and rivaled by 9.Nh3 and 8.Qf3.

10...Bd6 is Black's most common next move, and White usually replies with 11.d4, though 11.f4 is an alternative. One possible line is the Knorre Variation, continuing 11...Qc7 12.Bd2, although 11...exd3 (en passant) and 11...0-0 are more usual for Black.

Tenth move alternatives for Black include 10...Bc5, 10...Qc7 (Göring Variation), and 10...Qd4.

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Steinitz Variation: 8.Be2 h6 9.Nh6

9.Nh3 is a variation popularized by Wilhelm Steinitz. Although it did not bring Steinitz success in his famous 1891 cable match against Mikhail Chigorin, Bobby Fischer revived it in the 1960s. Nigel Short led a second revival of 9.Nh3 in the 1990s, and today it is thought to be about equal in strength to the more common 9.Nf3.^[8]

9.Nh3 became slightly more frequently played than 9.Nf3 in the 21st century, but it has still lost popularity overall due to the rise of 8.Bd3. Black's common replies include 9...Bd6, 9...Bc5, 9...g5, and 9...Bxh3.

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Bogoljubow Variation: 8.Qf3

8.Qf3 pins Black's pawn on c6 to the rook on a8. It is possible to sacrifice the rook with 8...cxb5 9.Qxa8, the Blackburne Variation, though more common are 8...Be7 (developing) and 8...Rb8 (unpinning).

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Kieseritzky Variation: 4.Ng5 d5 5.exd5 Na5 6.d3

Instead of retreating the bishop, White may instead play to hold the gambit pawn with this move. Paul Morphy preferred this line, named after Lionel Kieseritzky and also known as the Morphy Variation. It is relatively unpopular since Black obtains good chances for the pawn with 6...h6 7.Nf3 e4 8.Qe2 Nxc4 9.dxc4 Bc5 and White effectively concedes the bishop pair. David Bronstein once tried the piece sacrifice 8.dxe4!? with success, but its soundness is doubtful.^[4][9]

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Bd7 Variation: 6.Bb5+ Bd7 7.Qe2

• After 8.Ba4, Black can win material after 8...h6 9.Nf3 (or 9.Nh3 Qd4) e4, as White's knight must either retreat to g1 or move to e5, in which case 10...Qd4 wins material.
• After 6...Bd7, White usually responds with 7.Qe2, defending the bishop. Black may then reply with either 7...Bd6 or 7...Be7.

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Fritz Variation: 5...Nd4

German master Alexander Fritz (1857–1932) suggested 5...Nd4 to Carl Schlechter, who published analysis of the move in Deutsche Schachzeitung in 1904, concluding that it is fully viable.^[10] In 1907 P. S. Leonhardt disputed this assesment in his column for the Swedish journal Tidskrift för Schack, in which he advocated the now standard move (6.c3 b5) 7.Bf1!^[11]

6.d6 now is inferior. After 6...Qxd6 7.Nxf7? Qc6! simultaneously attacks the pawn on g2 and the bishop on c4, and if 8.Nxh8? (relatively best is 8.0-0, giving up the bishop) 8...Qxg2 9.Rf1 Qe4+ 10.Be2 Nf3#. White should instead play 7.Bxf7+ Ke7 8.Bb3 Nxb3 9.axb3 h6 10.Nf3 e4 11.Ng1 Kf7 and Black had good compensation for the pawn in Bogolyubov-Rubinstein, Stockholm 1919.^[12]

Instead, White's best reply is 6.c3, after which the game usually continues 6...b5 7.Bf1! Nxd5, followed by either 8.cxd4, 8.Ne4, or 8.h4.

The Berliner Variation, named after World Correspondence Chess Champion Hans Berliner, continues the Fritz sub-line 8.Ne4 with 8...Qh4, from the famous game Estrin–Berliner, World Correspondence Championship 1965–68, eventually won by Black; this win was pivotal to Berliner's eventual championship victory. That game, which saw Black embark on a very sharp sacrificial path, continued 9.Ng3 Bg4 10.f3 e4 11.cxd4 Bd6 12.Bxb5+ Kd8 13.0-0 exf3. In 1971, IM / GMC Estrin later published a suggestion of the move 14.Qb3!? as an improvement on the game continuation, and this possibility has continued to interest many players.^[13]

The 8.cxd4 line continues 8...Qxg5 9.Bxb5+ Kd8 10 0-0 (or 10.Qf3, when 10...Bb7 11.0-0 transposes, but 10...exd4 is also possible, as in Wei Yi vs. Jan-Krzysztof Duda, 2014 World Junior Chess Championship^[14]) 10...Bb7 11 Qf3 Rb8 12 dxe5 (not 12.Qxf7? Nf6, which defends against mate on d7 while threatening mate on g2 and 13...Bd5, trapping White's queen) 12...Ne3! 13.Qh3 Qxg2+ 14.Qxg2 Nxg2 15.d4, where White is a pawn up in a sharp position.^[15]

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Ulvestad Variation: 5...b5

This line is related to the Fritz Variation as they share a common subvariation. American master Olav Ulvestad introduced 5...b5 in a 1941 article in Chess Review.^[16] White has only one good reply, the counterintuitive 6.Bf1!, protecting the undefended pawn on g2, so White can answer 6...Qxd5? with 7.Nc3. Both replies 6.Bxb5 Qxd5 7.Bxc6+ Qxc6 and 6.dxc6 bxc4 7.Nc3 are weak for White. After 6.Bf1!, Ulvestad's first idea 6...h6? is refuted by 7.Nxf7!.^[17] The move 6...Nxd5, Ulvestad's second idea,^[18] is considered Black's best response.^{[by whom?]} Black can also transpose to the Fritz Variation with 6...Nd4, making another advantage of 6.Bf1 apparent; the bishop is not attacked as it would be if White had played 6.Be2.

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Fried Liver Attack: 6.Nxf7 Kxf7+ 7.Qf3+ Ke6 8.Nc3

This recapture is extremely risky. Albert Pinkus tried to bolster this move with analysis in 1943 and 1944 issues of Chess Review,^[19] but White gets a strong attack with either the Lolli Attack (6.d4), which Bobby Fischer thought to be very strong,^[20] or the sacrificial Fried Liver Attack (6.Nxf7), which leaves Black's king in the middle of the board after 6...Kxf7 7.Qf3+ Ke6 8.Nc3. These variations are usually considered too difficult for Black to defend over the board.

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Traxler Variation: 4.Ng5 Bc5

The Traxler Variation, also known as the Wilkes-Barre Variation, ignores White's attack on f7 with a bold counterattack on f2 and leads to wild play. Czech problemist Karel Traxler played it against Reinisch in Prague in 1890.^[21] Later, Frank Marshall named it after Wilkes-Barre, a town in Pennsylvania, claiming to be the first to analyze and publish it,^[22] so 4...Bc5 is known both as the Traxler Variation and, in the United States and the United Kingdom,^[23] the Wilkes-Barre Variation.

White can play 5.d4, 5.Nxf7, or 5.Bxf7+:

• After 5.d4 d5!, White's best move is 6.Bxd5, reapplying the pressure on f7.
• 5.Nxf7 is very complicated after 5...Bxf2+. The current main lines all are thought to lead to drawn or equal positions, e.g. after 6.Kxf2 Nxe4+ 7.Kg1, or even 7.Ke3.
• White's best try for an advantage is probably 5.Bxf7+ Ke7 6.Bb3, although some writers such as Lawrence Trent recommend 6.Bd5.^[8] No grandmasters have regularly adopted the Wilkes-Barre as Black, but Alexander Beliavsky and Alexei Shirov have played it occasionally even in top competition. Beliavsky even ventured it twice, holding then-World Champion Karpov to a draw and defeating Anand.^[24][25] No clear refutation is known.
  A tricky variation is 5.Bxf7+ Kf8!?, where Black plays for one last trick with 6.Bb3 d6 7.Nf7 Qe7. If White plays the seemingly standard 8.Nxh8??, Black is now winning after 8...Bg4!! 9.f3 Nxe4, making use of the pinned f3-pawn. This pawn cannot capture the bishop as 10.fxg4?? Qh4+ 11.g3 Bf2+ wins by force for Black.

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4...Nxe4

4...Nxe4?! is considered unsound but must be handled carefully. 5.Nxe4 d5 poses no problems for Black. If 5.Nxf7? Qh4! 6.g3 (6.0-0 Bc5!) 6...Qh3 7.Nxh8 Qg2 8.Rf1 Nd4 9.Qh5+ g6 10.Nxg6 hxg6 11.Qxg6+ Kd8 and Black has dangerous threats.^[26] (Alternatively, after 5.Nxf7? Qh4! 6.g3, Black could play more aggressively 6...Nxg3! 7.fxg3 Qe4+ 8.Qe2 Qxh1+ 9.Qf1 Qxf1+ 10.Kxf1 d5 11.Bxd5 Bh3+ 12.Ke1 Nb4 13.Bb3 Nxc2+ 14.Bxc2 Kxf7 with a distinct advantage of material for Black.) Correct is 5.Bxf7+! Ke7 6.d4! (6.d3 is also good) and now:

• 6...d5 7.Nc3! (best, discovered by Soviet player Lopukhin; White has a clear advantage) 7...Nxc3 8.bxc3 Qd6 (8...Bf5 9.Qf3±; 8...e4 9.f3!) 9.a4! Kd8 10.Bg8! Ke8 11.Bxh7± (Estrin).^[27][26]
• 6...h6 7.Nxe4 Kxf7 and now 8.dxe5 Qe8 9.f4 d6 10.0-0 (±) Kg8 11.Nbc3 dxe5 12. f5 Qf7 13.Nd5 Bd7 14.f6 g6 15.Ne7+! and White has excellent chances (Estrin).^[27][26]

The quiet 4.d3 is White's most common fourth move. It is sometimes called the Modern Bishop's Opening,^[28], being commonly reached from the Bishop's Opening via 2.Bc4 Nf6 3.d3 Nc6 (the most notable alternative being 3...c6) 4.Nf3. By playing d3, White tries to avoid the tactical battles that are common in other lines of the Two Knights and to enter a more positional game. The resulting positions take on some characteristics of the Ruy Lopez if White plays c3 and retreats the bishop to c2 via Bc4–b3–c2. This move became popular in the 1980s and has been used by John Nunn and others.

The most common response for Black is to play 4...Bc5, transposing to the Giuoco Pianissimo. Also common are 4...Be7, 4...h6, and 4...d5.

This line is also commonly reached from the Hungarian Defense when White opts out of the lines with d4.

This intends 5...d6. 4...d6?! should not be played due to 5.Ng5, where Black must play 5...d5, transposing to the Knight Attack with White having played the extra move d3. Black often ends up playing ...g5 or ...g6.

This is significantly less common than the other three options. It is a dynamic but risky line.

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Open Variation: 4.d4 exd4

White's move 4.d4 intends rapid development. After the usual response 4...exd4, this leads to a position also commonly reached via the Scotch Gambit (3.d4 exd4 4.Bc4). The transposition occurs with the most common response to the Scotch Gambit, 4...Nf6. White can respond with 5.e5 (the most common move), 5.0-0, or 5.Ng5.

After 5.0-0, Black is considered to equalize by eliminating White's last center pawn with 5...Nxe4, after which White usually plays 6.Re1, though 6.Nc3 (Nakhmanson Gambit) is a notable alternative. After 6.Re1, the usual continuation is 6...d5 7.Bxd5 Qxd5 8.Nc3, the Anderssen Attack. The most notable sideline is 6...d5 7.Nc3, the Canal Variation.

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Anderssen Attack: 5.0-0 Nxe4 6.Re1 d5 7.Bxd5 Qxd5 8.Nc3

In this line, White will regain the material, but Black is judged as having a comfortable position after 8...Qa5 or 8...Qh5.

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Nakhmanson Gambit Accepted: 5.0-0 Nxe4 6.Nc3 dxc3

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Nakhmanson Gambit Declined: 5.0-0 Nxe4 6.Nc3 Nxc3 7.bxc3

If Black accepts the piece with 6...dxc3 and then after the usual continuation 7.Bxf7+ Kxf7 8.Qd5+ makes the intuitive move 8...Ke8?!, White is seen as receiving adequate compensation. Instead, 8...Kf6! has been analyzed to offer Black a substantial edge with best play.

A common alternative is to return the knight with 6...Nxc3 7.bxc3 d5 8.Bb5 Be7, leading to a better position for Black.^[29]

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5.0-0 Bc5 6.e5 d5

Alternatively, Black can invite White to enter the extensively analyzed Max Lange Attack after 5...Bc5, with White accepting via the usual continuation 6.e5 d5. It can also arise by transposition from the Giuoco Piano or Scotch Gambit.

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Advance Variation: 5.e5

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Main line: 5.e5 d5 6.Bb5 Ne4 7.Nxd4 Bd7 8.Bxc6 bxc6 9.0-0 Bc5 10.f3 Ng5

White can choose to avoid these lines by playing 5.e5, a line often adopted by Evgeny Sveshnikov, which has gradually become the main line of the Open Variation. After 5.e5, either 5...Ne4 or 5...Ng4 is a playable reply, but most common and natural is 5...d5 6.Bb5 Ne4 7.Nxd4 Bc5, with sharp play.

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5.Ng5