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

Philidor defence Philidor defence 3. d4 White attacks e5 again and threatens to win the pawn. Black must deal with the threat: trade, defend, or counterattack? Trade the pawn If Black allows White to trade into them, dxe5, Black won't even be able to recapture using their d-pawn because it is pinned to their queen, so doing so would allow an unfavourable queen trade. Most straightforwardly then, Black should trade first. 3...exd4 is the exchange Philidor. This is the main line. Defend the pawn Black can try defending the pawn. The chief way to do so is 3...Nd7, the Hanham variation. White usually replies 4. Bc4, targeting the vulnerable f7 pawn and threatening a mating trap if Black continues to develop normally. No other defence is sound: 3...Bg4 is a popular amateur reply, but doesn't succeed in defending the pawn. Though Black thinks to pin the knight to White's queen, after 4. dxe5 dxe5 5. Qxd8+ (trades queens and unpins the knight) Kxd8, White's knight is unpinned and can take back on e5 anyway. If 4... Bxf3 first, as in the Opera Game, 5. Qxf3 dxe5 6. Bc4 and White is threatening a crushing attack on f7. But, 3...Bg4?! can be used to gambit the pawn (see below) 3...Nc6?! (transposing into a sort of 'declined' Scotch game) is unpalatable for Black. While this looks like a more natural square for the knight than d7, it can be met with either 4. e5, kicking the knight, or 4. Bb5, pinning it (as a consequence of Black having played d6 first) and transposing into a Old Steinitz Spanish, which is not a defence held in very high regard. 3...f6? defends e5 with the f pawn, but gives White more time to extend their development lead and exploit the weakened kingside. Counterattack Or, Black can leave the pawn undefended and counterattack White's e-pawn instead. There are two approaches: 3...Nf6, the Nimzowitsch variation, plans to meet 4. dxe5 with 4...Nxe4, after which the natural looking 5. exd6? Bxd6 leads to equality for Black. 3...f5?! was Philidor's Romantic recommendation, with the understanding that trading a more peripheral f-pawn to eliminate the more valuable central e-pawn is surely advantageous. White has their choice of captures 4. dxe5?! fxe4 (kicks knight) 5. Ng5 d5 and while the engine still favours White, the position is unusual and perilous. 4. exf5 and the pawn can be recovered by 4...Bxf5, or the knight kicked first with 4...e4. However, 3...f5?! is simply too weakening. 4. Bc4 and Black is soon facing a choice of allowing a fork by Nf7 or Qh4+ and the annihilation of their kingside. Gambit the pawn While 3...Bg4 doesn't defend the e5 pawn (see above), it allows Black to gambit it and play 4...Nd7, the Albin-Blackburne gambit. Black gives up their two central pawns for one of White's central pawns and sped up development. Theory table 3...exd4 4. Nxd4 Nf6 5. Nc3 Be7 6. Bf4 O-O 7. Qd2 Nc6 8. O-O-O Nxd4 9. Qxd4 Be6 10. f3 Exchange variation ⩲ 3... ... 4. ... ... 5. ... ... 6. Be2 O-O 7. O-O Re8 8. f4 (White castles short) = 3... Bg4!? 4. dxe5 Bxf3? 5. Qxf3 dxe5 6. Bc4 Qf6 7. Qb3 ± 3... ... 4. ... Nd7 5. exd6 Bxd6 6. Be2 Qe7 Albin-Blackburne gambit 3... Nd7 4. Bc4 c6 5. O-O Be7 6. dxe5 dxe5 7. Ng5 Bxg5 8. Qh5 Qe7 9. Qxg5 Qxg5 10. Bxg5 Hanham variation ± 3...Nf6 4. dxe5 Nxe4 5. Qd5 Nc5 6. Bg5 Qd7 7. exd6 Bxd6 8. Nc3 O-O 9. O-O-O Nimzowitsch variation ⩲ References Philidor Defence