2.Nf3

The idea

2.Nf3 is a flexible move: White develops and waits to see what Black does before deciding on the d-pawn. Black plays 2...d5 anyway.

Now 3.Nc3 transposes to the Two Knights Variation and 3.d3 to the Breyer Variation. 3.exd5 cxd5 and 3.e5 Bf5 usually lead, once White plays d4, to the Exchange and Advance Variations with White's knight already on f3.

Plans for White

White keeps every option: d4 for a classical center, d3 for the quieter Breyer Variation, or Nc3 for the Two Knights. With the knight out first, White has chosen calm development over an early pawn storm, so the sharpest Advance lines with g4 and h4 are less likely.

Plans for Black

Play 2...d5, then follow the plan for the structure White chooses. After 3.exd5 cxd5, develop with ...Nc6 and ...Nf6 and bring the bishop out to f5 or g4. After 3.e5, put the bishop on f5 before playing ...e6, exactly as in the Advance Variation.

Watch out for

For Black, the Apocalypse Attack: 3.exd5 cxd5 4.Ne5. The natural 4...Bf5? runs into 5.Bb5+, and Black has to lose time answering the check. 4...e6 is the move played most often, and 4...g6 is considered critical.

For White, the knight move commits to little, which cuts both ways: if White never plays d4, Black's pawn on d5 controls the center and Black develops freely.