Chess Opening Theory/1. e4/1...e5/2. Nf3/2...d6/3. d4/3...Nc6

This is an uncommon way of playing the Philidor defence, as while the knight on c6 defends the e5 pawn, it may be pinned with Bb5. This position can arise in the Scotch game if Black declines to trade on d4 by playing 3...d6 instead.

White attacks e5 twice and Black appears to defend it twice. If White trades in the centre, 4. dxe5?! Nxe5 5. Nxe5 dxe5 6. Qxd8+ Kxd8 Black loses castling rights, but the queens are off the board and the position is close to even.

4. Bb5, pinning the knight to the king, removes a defender of e5 first. This is a transposition into the Old Steintiz defence in the Spanish game.

The Stockfish choice is 4. d5 Ne7 5. c4, closing the centre while gaining time on the knight and expanding on the queenside.

Various other transpositions are possible:

• 4. Nc3 transposes to the Three Knights Opening.
• 4. Bc4 transposes to the Semi-Italian Opening.
• 4. c3 transposes to the Ponziani Opening.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

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Wikipedia has related information at Philidor Defence.