Three Knights Variation

The Three Knights Variation arises when White develops both knights before deciding where the c1-bishop belongs. It is usually reached through 1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 rather than through the 1. d4 d5 order. The sequence suits both players. White avoids the Nimzo-Indian that 3. Nc3 would allow, and Black avoids the Exchange Variation. The cost for White is that the early Nf3 rules out the plans based on Nge2 and f3.

The engine considers the position balanced, and Black has a wide choice of replies. The two most popular are almost equally common. After 4...Be7, 5. Bg5 transposes into the traditional lines of the parent opening. White can avoid that with 5. Bf4, the Harrwitz Attack, which develops the bishop outside the pawn chain on a more active diagonal.

4...Bb4, the Ragozin Defense, pins the c3-knight in Nimzo-Indian fashion while keeping the pawn on d5. White's main tries are 5. Bg5, 5. cxd5 and the Alekhine Variation, 5. Qa4+. After 5. Bg5 dxc4 6. e4, play enters Vienna territory. The Vienna Variation proper, 4...dxc4, surrenders the center at once. The main line, 5. e4 Bb4 6. Bg5, gives White central occupation in return for lasting weaknesses in the pawn structure. Fine–Euwe at AVRO 1938 is a well-known high-level example. 5. e3 is the calmer Quiet Variation.

4...c5, the Semi-Tarrasch Defense, challenges the center immediately and usually recaptures on d5 with the knight. The Endgame Line, 5. cxd5 cxd4 6. Qxd4 exd5 7. e4 dxe4 8. Qxd8+ Kxd8, removes the queens early. It has a reputation as a drawing line and has been used for that purpose by Wesley So, Anish Giri and Magnus Carlsen. In the Exchange Variation, 5. cxd5 Nxd5 6. e4 Nxc3 7. bxc3 cxd4 8. cxd4, White gets a broad pawn center. Ding Liren, Vladimir Kramnik, Giri and Carlsen have all played it.

4...c6 transposes into the Semi-Slav Defense. Less common choices are 4...Nc6, the Chigorin Defense, after which White scores best among the main replies, and 4...Nbd7, the Barmen Variation. Across all lines White scores somewhat better than Black, in keeping with the parent opening.