Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. d4/3...exd4/4. Bc4

White temporarily forgoes recapturing the d4 pawn, instead developing the light-squared bishop to the most active square targeting the f7 pawn. There's no great way for Black to hold on to the pawn they are temporarily up.

4...Bc5, the Haxo gambit and second most common move, is the only way to add another defender to the pawn on d4. Though Black has two defenders to White's two attackers, after 5. c3 Black is best advised to give the pawn back.

This is because 5...dxc3?, thinking White wants 6. Nxc3 and Black will still be ahead a pawn, loses to 6. Bxf7+! Kxf7 7. Qd5!+. White can recapture the bishop and if Black still tries to cling onto the material, they fall behind too far in position and development, e.g. 7...Ke8 8. Qh5+ (a little trick to either take the bishop with check or force Black to weaken their kingside) g6 9. Qxc5 cxb2 10. Bxb2+-.

Instead, Black's idea is to return the pawn with 5...Nf6, transposing into the Greco gambit for an even game, or 5...d3.

4...Nf6 is the most played move, developing the knight and attacking the pawn on e4. This position can also arise out of the Italian game, after 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. d4 exd4.

After 4...Nf6, White usually responds either with 5. e5, where they recover the pawn with the sequence 5. e5 d5 6. Bb5 Ne4 7. Nxd4 Bd7, or 5. O-O, sacrificing the other pawn by allowing 5...Nxe4, the double gambit accepted. 6. Re1 doesn't win the knight outright, rather the game continues 6...d5 7. Bxd5 Qxd5 8. Nc3! (d-pawn is pinned) and 9. Nxe4 after the queen moves.

4...Bb4+, the London defence, seeks to capitalise on Black's control of c3 while they can. 5. c3 dxc3 6. O-O cxb2 7. Bxb2 and while White is down two pawns, they have more than enough compensation in rapid development and activity.

4...Be7, is called the Benima defence. Black simply gets a piece off the back rank to make way for castling, and allows White to retake d4 straight away. This resembles the Hungarian defence to the Italian opening, if Black accepted the pawn on d4. Black's position is conservative: the bishop is not optimally placed on e7, but it is solid enough.

1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Bc4

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