Key ideas
- The main replies are 3...Nf6, the Jaenisch Counterattack, and 3...d5. Both strike at e4 before White's d4 arrives.
- After 3...Nf6 4.d4 Nxe4 5.d5, White gains time against the knights. Black usually answers with 5...Ne7 or 5...Nb8, while 5...Bc5 is the sharper Vukovic Gambit.
- After 3...d5, 4.Qa4 pins the knight on c6 and threatens Nxe5. Black replies with 4...f6, 4...Bd7 or 4...Nf6, the Leonhardt Variation.
- The quiet 4.d3 against the Jaenisch avoids theory and leads to slow positions with Nbd2, Be2 and castling.
Plans for White
Play d4 as soon as it is safe and use the c3-d4-e4 centre to gain space. The queen often goes to a4 to pin the c6 knight while Black's development is incomplete.
Plans for Black
Strike in the centre before d4 arrives, with 3...Nf6 or 3...d5. White's queen's knight has lost its best square, so active piece play pays off for Black.