Two Knights Defense

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(s)	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^[2] (c. 1550 – c. 1610) in the late 16th century, this line of the Italian Game was extensively developed in the 19th century. Black's third move is a more aggressive defense than the Giuoco Piano (3...Bc5). White may attack Black's weak pawn on f7 with 4.Ng5. If White does so, the game quickly takes on a tactical character: Black is practically forced to give up a pawn for the initiative. The complications are such that David Bronstein suggested that the term "defense" does not fit, and that the name "Chigorin Counterattack" would be more appropriate.^[3] However, White most often opts for the quieter 4.d3. The Two Knights has been played and analyzed by many aggressive players including Mikhail Chigorin, Paul Keres, and world champions Mikhail Tal and Boris Spassky.

This move creates a double attack on Black's pawn on f7, as White's bishop on c4 also targets the square. If the knight were to capture the pawn, this would fork Black's queen and rook. If the bishop were to capture instead, Black's king would be forced to move and lose castling rights. Unlike in the Giuoco Piano, Black's queen cannot capture on g5 to prevent the attack. Although the move practically wins a pawn by force and weakens the protection of Black's king, Black can gain compensation with precise play through quick piece development and gaining tempo by forcing White's pieces to retreat. German master Siegbert Tarrasch called 4.Ng5 "a real duffer's move" (ein richtiger Stümperzug) and Soviet opening theorist Vasily Panov called it "primitive", but despite such criticism, 4.Ng5 has remained a popular choice for White at all levels, with only 4.d3 being more common for White. It was very common in the 19th century. The move is sometimes referred to as the Knight Attack. In the modern day, the name Fried Liver Attack is often used informally with the same meaning. However, traditionally, that name refers only to the line 4...d5 5.exd5 Nxd5 6.Nxf7.

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Main line after 10...Bd6

After 4...d5 White has little option but to play 5.exd5, since both the bishop and e4-pawn are attacked. Then Black most often plays 5...Na5, known as the Polerio Defense.^[4][5] Play usually continues 6.Bb5+ c6 (6...Bd7 is also possible^[6]) 7.dxc6 bxc6.

White's most common next moves are 8.Be2, 8.Bd3, and 8.Qf3 (the Bogoljubow Variation). One common line is 8.Be2 h6 9.Nf3 e4 10.Ne5 Bd6 (see diagram). This is the Knorre Variation. After ten moves, White has developed only two pieces against Black's three pieces and pawns, but has an extra pawn as well as a better pawn structure. 10...Bc5 is a viable alternative for Black, as is 10...Qc7 (the Göring Variation).^[7] Wilhelm Steinitz favored 9.Nh3, although it did not bring him success in his famous 1891 cable match against Mikhail Chigorin. Known as the Steinitz Variation, the move remained rare until 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.^[6]

White can instead play to hold the gambit pawn with 6.d3. Paul Morphy preferred this line, known as Kieseritzky Variation or Morphy Variation, but 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.^[3][8]

There are also various fifth move alternatives for Black:

• The Fritz Variation 5...Nd4 and Ulvestad's Variation 5...b5 are related as they share a common subvariation. American master Olav Ulvestad introduced 5...b5 in a 1941 article in Chess Review. White has only one good reply: 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. Black's best response is to 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. German master Alexander Fritz (1857–1932) suggested 5...Nd4 to Carl Schlechter, who wrote about the idea in a 1904 issue of Deutsche Schachzeitung. In 1907 Fritz himself wrote an article about his move in the Swedish journal Tidskrift för Schack. White's best reply is 6.c3, where the game usually continues 6...b5 7.Bf1 Nxd5, followed by 8.cxd4, 8.Ne4, or 8.h4. White may instead play 6.d6, resuming the double attack on f7. Black usually responds with 6...Qxd6, apparently allowing a fork of Black's queen and rook by the knight, but in the line 7.Nxf7? Qc6, White cannot protect the pawn on g2 without giving up the bishop on c4 or allowing the fork Nxc2+, a similar theme to the line with 6...Qxd5? mentioned earlier. If White ignores the threat, such as with 8.Nxh8 Qxg2 9.Rf1, Black wins White's queen after 9...Qe4+ or 9...Bg4.
• The recapture 5...Nxd5?! is extremely risky. Albert Pinkus tried to bolster this move with analysis in 1943 and 1944 issues of Chess Review, but White gets a strong attack with either the safe Lolli Attack (6.d4), which Bobby Fischer thought to be very strong,^[9] or the sacrificial Fried Liver Attack (6.Nxf7), which usually continues 6...Kxf7 7.Qf3+ Ke6 8.Nc3, leaving Black's king almost in the middle of the board. These variations are usually considered too difficult for Black to defend over the board, but they are still occasionally played. Lawrence Trent describes 5...Nxd5 as "a well-known bad move" (or words to that effect).^[6]
• The Berliner Variation, named in honor of IM / GMC Dr. 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.^[10]

This bold move ignores White's attack on f7 and leads to wild play. Czech problemist Karel Traxler played it against Reinisch in Prague in 1890.^[11] Later it was named after Wilkes-Barre, Pennsylvania by Frank Marshall, who claimed to be first to analyze and publish it,^[12] so today 4...Bc5 is known as both the Traxler Variation and (in the United States and the United Kingdom^[13] only) 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 6.Bd5 was the move recommended by Lawrence Trent),^[6] as this poses Black the most problems. No grandmasters have regularly adopted the Wilkes-Barre as Black, but Alexander Beliavsky and Alexei Shirov have played it occasionally even in top competition. Belyavsky even once venturing it against ex-World Champion, Karpov, and held him to a draw. 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.

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.^[14] (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).^[15][14]
• 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).^[15][14]

White can choose to develop rapidly with 4.d4 exd4 5.0-0. Now Black can equalize simply by eliminating White's last center pawn with 5...Nxe4, after which White regains the material with 6.Re1 d5 7.Bxd5 Qxd5 8.Nc3, but Black has a comfortable position after 8...Qa5 or 8...Qh5.

The wild Nakhmanson Gambit 6.Nc3 gives White compensation if Black accepts the piece with 6...dxc3 7.Bxf7+ Kxf7 8.Qd5+ and then makes the intuitive move 8...Ke8?! Instead, 8...Kf6! has been analyzed to offer Black a substantial edge with best play. Victor Bologan suggests declining the gambit with 6...Nxc3 7.bxc3 d5 8.Bb5 Be7 leading to a better position for Black.^[16]

Alternatively, Black can enter the extensively analyzed Max Lange Attack after 5...Bc5 6.e5 d5, which can also arise by transposition from the Giuoco Piano or Scotch Game. White can choose to avoid these lines by playing 5.e5, a line often adopted by Sveshnikov. 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. The tricky 5.Ng5?! is best met by 5...d5! 6.exd5 Qe7+!

The quiet move 4.d3, the Modern Bishop's Opening,^[17] transposes into the Giuoco Pianissimo if Black responds 4...Bc5, but there are also independent variations. The other most common responses are 4...Be7 and 4...h6, which typically lead to closed, positional games. The fourth most common response is 4...d5, a dynamic but risky line where Black intends to open the game. 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 attempt to defend the pawn with 4.Nc3 does not work well since Black can take the pawn anyway and use a fork trick to regain the piece, 4.Nc3?! Nxe4! 5.Nxe4 d5. The try 5.Bxf7+? does not help, as Black has the bishop pair and a better position after 5...Kxf7 6.Nxe4 d5. Instead, 4.Nc3 is usually played with the intent to gambit the e-pawn with the Boden–Kieseritzky Gambit, 4.Nc3 Nxe4 5.0-0. This gambit is not commonly seen in tournament play as it is not well regarded by opening theory, but it can offer White good practical chances, especially in blitz chess.

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Traxler or Wilkes-Barre Variation

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Main Line

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Boden–Kieseritzky Gambit

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Max Lange Attack

White must respond to the attack on the e-pawn. (For explanation of notation, see chess opening theory table.)

1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6

Bibliography

• de Firmian, Nick (1999). Modern Chess Openings: MCO-14. Random House Puzzles & Games. ISBN 0-8129-3084-3.
• Estrin, Yakov (1971). The Two Knights' Defence (English ed.). Chess Ltd.
• Harding, Tim; Botterill, G. S. (1977). The Italian Game. B. T. Batsford Ltd. ISBN 0-7134-3261-6.
• Hooper, David; Whyld, Kenneth (1996) [First pub. 1992]. The Oxford Companion to Chess (2nd ed.). Oxford University Press. ISBN 0-19-280049-3.
• New in Chess Yearbook 55. New in Chess. 2000. ISBN 90-5691-069-8.
• Pinski, Jan (2003). The Two Knights Defence. Everyman Chess. ISBN 1-85744-283-0.
• Unzicker, Wolfgang (1975). Knaurs Neues Schachbuch für Anfänger und Fortgeschrittene. Droemer Knaur. ISBN 3-426-02242-7.

• Beliavsky, Alexander; Mikhalchishin, Adrian (1999). The Two Knights Defense. Batsford. ISBN 978-0-7134-8441-0.
• Tait, Jonathan (2004). The Two Knights Defence. Everyman Chess. ISBN 978-1857442830.

The Wikibook Chess Opening Theory has a page on the topic of: Nakhmanson Gambit

The Wikibook Chess Opening Theory has a page on the topic of: Two Knights Defense

• Harding, Tim (March 2001). The Kibitzer: Two Knights Defense, Part 1 (PDF). Chesscafe.com.
• Harding, Tim (April 2001). The Kibitzer: Two Knights Defense, Part 2 (PDF). Chesscafe.com.
• Harding, Tim (May 2001). The Kibitzer: Two Knights Defense, Part 3 (PDF). Chesscafe.com.