The Four Knights Game is a chess opening that begins with the moves: 1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6
This is the most common sequence, but the knights may in any order to reach the same position.
The opening is fairly popular with beginners who strictly adhere to the opening principle: "Develop knights before bishops." It was one of the workhorses in the family of the Open Game, at even the highest levels, until World War I. Thereafter it fell by the wayside, along with a number of other Open Games. In this period ambitious players explored the Ruy Lopez, believing it a better attempt by White to exploit the advantage of the first move. In the 1990s, this opening saw a renaissance, and is now seen in the praxis of players from beginner to grandmaster.
The Four Knights usually leads to quiet , though there are some variations. The Encyclopaedia of Chess Openings has three codes for the Four Knights Game: C49: 4.Bb5 Bb4 (Symmetrical Variation) C48: 4.Bb5 without 4...Bb4 C47: 4.d4 and others
Variations
4.Bb5
White's most common move is 4.Bb5, the Spanish Variation. This variation can also be reached from the Ruy Lopez, Berlin Defence. After 4.Bb5, Black has four major alternatives.
The first of these is 4...Bb4, the Symmetrical Variation known as the Double Spanish Variation. Black can play more aggressively by 4...Nd4, the Rubinstein Variation. White cannot win a pawn with 5.Nxe5, since Black regains the pawn with the advantage of the after 5...Qe7 6.Nf3 (6.f4 Nxb5 7.Nxb5 d6) Nxb5 7.Nxb5 Qxe4+ 8.Qe2 Qxe2+ 9.Kxe2 Nd5 10.c4 a6 White most often plays 5.Ba4, when Black usually continues in gambit fashion with 5...Bc5 6.Nxe5 0-0 7.Nd3 Bb6 8.e5 Ne8 followed by ...d6. Another line, which discourages many ambitious Black players from playing the Rubinstein, is 5.Nxd4 exd4 6.e5 dxc3 7.exf6 Qxf6 (7...cxd2+ 8.Bxd2 Qxf6 9.0-0 is dangerous for Black) 8.dxc3 Qe5+. This often leads to a quick draw after 9.Qe2 Qxe2+. The classical move 4...Bc5 is perfectly , see the famous game Louis Paulsen–Paul Morphy from the First American Chess Congress (1857). In recent years, Black has tried 4...Bd6!? with varying results. That move takes the sting out of 5.Bxc6, which is met with 5...dxc6 with a good game. If White plays , Black will regroup with ...0-0, ...Re8, ...Bf8, and ...d6.
4.d4
If White plays 4.d4, the Scotch Four Knights Game arises. This leads to a more , which can also be reached from the Scotch Game, e.g. 1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 5.Nc3. This variation was played in the fifth game of the 1996 Deep Blue versus Garry Kasparov match.
One reason White may choose the Four Knights (3.Nc3) move order over the Scotch (3.d4), besides fearing that after 3.d4 exd4 4.Nxd4 Black may choose 4...Bc5 or 4...Qh4, is that White may want to play the Belgrade Gambit (1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.d4 exd4 5.Nd5!?). It is not possible to reach the Belgrade from the Scotch; however, the Belgrade is a distant second in popularity to 5.Nxd4.
4.Bc4
A further possibility is 4.Bc4, the Italian Four Knights Game, or Prussian Four Knights Game, popular in the 1880s, though this line is regarded as inferior according to Pinski, and an outright mistake by IM Larry D. Evans. Black can preserve the symmetry by 4...Bc5, leading to the quiet Giuoco Pianissimo. A better move order for White that leads to this position is via the Giuoco Piano by 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Nc3 Nf6. The line is a favourite among younger players due to its simple and easy development, but was also used successfully by Nigel Short against Antoaneta Stefanova.
The problem with playing for this position via the Four Knights Game is that after 4.Bc4, Black can perform the center fork trick by pseudo-sacrificing a knight with 4...Nxe4!. Then 5.Bxf7+?, though superficially attractive, relinquishes the bishop pair and central control to Black. After 5...Kxf7 6.Nxe4 d5 7.Neg5+ Kg8, Black is already threatening 8...e4, and after 8.d3 h6 9.Nh3 Bg4, Black has a very powerful position, with an unopposed light-squared bishop, a strong duo of pawns in the centre, and a safe king, while White needs to work out how to get the displaced knight on h3 into play; often it will need to be played back to g1.