Chess Opening Theory/1. e4/1...e5/2. Nf3/2...d6/3. Bc4

3. Bc4 is a sideline in the Philidor defence. White develops a bishop to a strong diagonal, targeting Black's weak f7 pawn.

Black usually continues 3...Be7, developing their bishop to the only available square and preparing to castle. Play usually continues 4. d4 dxe4 and the game resembles an Exchange Philidor (3. d4 exd4) where White has played Bc4.

Alternatively, White can play the more conservative 4. d3 instead, since they have already developed their king's bishop outside of the pawn chain. Playing 4. c3 (followed by 5. d3) is called the Steinitz variation, after a game Wilhelm Steinitz played against George MacDonnell^[1] This leads to a more closed game.

3...f5?!, the Lopez countergambit, is an aggressive alternative where Black assaults White's centre with a flank pawn. White can take first, 4. exf5, but this gives up an important central pawn and Black gets to recapture while developing 4...Bxf5. Nevertheless, Black's situation with their passive kingside bishop is still grim.

Defending the pawn with 4. d3, so that White can recapture and keep a pawn on e4, is a straightforward option.

The strongest reply is 4. d4!. If 4...fxe4, then White can take on e5 5. Nxe5 as 5...dxe5? is answered with 6. Qh5+ g6 7. Qxe5+, winning the rook in the corner. If 4...exd4, then while White could take back with 5. Nxd4, the engine line is actually to focus on development first: having played four pawn moves in the opening, Black is disastrously behind.

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

1. e4 e5 2. Nf3 d6 3. Bc4

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Wikipedia has related information at Philidor Defence

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.