Key ideas
- After 3.d4, Black can hold the centre with 3...Nf6 and ...Nbd7 (the Lion and Hanham setups), give it up with 3...exd4 (the Exchange Variation), or play the sharp Philidor Countergambit, 3...f5.
- In the Hanham and Lion structures, Black keeps a pawn on e5 with pieces on d7, e7 and f6, then plays ...c6, ...O-O and often ...Qc7, ...Re8 or queenside expansion with ...b5.
- In the Exchange Variation, Black concedes the centre but gets free development with ...Nf6, ...Be7 and ...O-O, and a later ...Re8 or ...d5 to challenge e4.
- Move order matters. 3...Nd7 at once allows 4.Bc4, hitting f7, so Black must reply precisely with 4...c6. Many players prefer 3...Nf6 4.Nc3 Nbd7, the Lion Variation.
Plans for White
Take space with d4, develop with Nc3, Bc4 or Be2 and castle short. The f7 square is the target in the early phase, and in the middlegame the extra space lets White prepare a kingside or queenside pawn advance.
Plans for Black
Keep the e5 pawn, finish development with ...Be7, ...O-O and ...c6, and look for queenside play with ...b5 or a well-timed ...exd4 to open the e-file for the rook.
Watch out
3.d4 Nd7 4.Bc4 Be7? loses material after 5.dxe5. If 5...dxe5, 6.Qd5 threatens mate on f7, and 6...Nh6 7.Bxh6 wins a piece, since 7...gxh6 8.Qxf7#. That is why Black answers 4.Bc4 with 4...c6.