Four Knights Game

With 3...Nf6 the position becomes fully symmetrical. White's 3. Nc3 protects e4 instead of challenging Black immediately, so the opening turns on how White uses the move in hand. Its reputation is drawish and its typical play positional, though several branches are sharp. It is often reached by transposition, for instance from the Scotch Game after 3. d4 exd4 4. Nxd4 Nf6 5. Nc3. It also lets White avoid the Petrov Defense, since after 1. e4 e5 2. Nf3 Nf6 3. Nc3 Black's best is considered to be 3...Nc6.

At master level the principal tries are 4. Bb5 and 4. d4. The Spanish Variation, 4. Bb5, resembles the Ruy Lopez, but the knight on c3 blocks the usual c3 and d4 plan, and because e4 is already covered, ...a6 followed by Bxc6 and Nxe5 works differently. Black's main answers are the mirroring 4...Bb4, the Double Spanish, where 5. O-O O-O 6. d3 d6 produces a closed, symmetrical game, and 4...Nd4, the Rubinstein Variation, which unbalances matters but can be met by the drawish exchange 5. Nxd4.

The Scotch Variation, 4. d4, aims to eliminate the e5 pawn and open lines for White's pieces. Its main line, 4...exd4 5. Nxd4 Bb4 6. Nxc6 bxc6 7. Bd3, appeared in game five of the 1996 Deep Blue versus Kasparov match. After 4...exd4 White can instead play 5. Nd5, the Belgrade Gambit, which cannot arise from the Scotch Game move order, while 4...Bb4 5. Nxe5 is the Krause Variation.

Online, 4. Bc4, the Italian Variation, is the most frequent choice, yet it permits the fork trick 4. Bc4 Nxe4 5. Nxe4 d5, after which Black recovers the piece and gains central influence; 4...Bc5 instead heads for the Giuoco Pianissimo. The Glek System, 4. g3, fianchettoes the bishop and follows with d3 in King's Indian Attack style, giving a less drawish game. The waiting moves 4. a3, the Gunsberg Variation, which prevents ...Bb4, and 4. h3, which Anish Giri brought into fashion, effectively hand Black the Four Knights with colors reversed. More speculative are the Halloween Gambit, 4. Nxe5, a dubious piece sacrifice for a pawn and a lead in development, and 4. Nd5, the Naroditsky Variation, which abandons e4 and was a blitz favorite of Daniel Naroditsky.

The opening has been known since the 16th century and enjoyed wide use in the 19th, but lost ground by the First World War as the Ruy Lopez came to be seen as the more ambitious try. It revived in the 1990s and again features in grandmaster repertoires. Engines assess the starting position as roughly balanced, favoring 4. d4, 4. h3 and 4. Bb5.