Scotch Invitation Declined

After 3...Nf6 4. d4, the standard reply is 4...exd4, which transposes into the Scotch Gambit. With 4...d6 Black instead holds the e5-pawn, refusing the transposition and keeping a Philidor-like structure. The cost is that the c8-bishop and the f8-bishop's development are both restricted, while White keeps the initiative in the center. The engine gives White a slight advantage, and White scores well in online games.

The usual answer, played in about half of the games, is 5. dxe5, releasing the tension. After 5...dxe5 6. Qxd8+ Nxd8 7. Nxe5 Nxe4, the queens are off early and the game enters a simplified middlegame. 5. d5 is a more ambitious alternative. It gains space and drives the c6-knight from its post, leading to a closed center similar to some Philidor and King's Indian structures. 5. Ng5, aiming at the weakened f7-square, is less common but has the best results for White of the main tries. Engines also suggest quiet development with O-O or Nc3. The line is a secondary choice and is chosen far less often than 4...exd4.