Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Bxc6/4...dxc6

Black takes the bishop and opens lines for their pieces.

If White takes the e5 pawn, 5. Nxe5?, Black can win it back tactically with ...Qd4!. Therefore White must first defend e4, so as to reinforce the threat. Black can functionally end the threat with ...f6, after which if White continues to pressure with d4, most of the lines lead to an early endgame.

5. O-O defends against Nxe5 Qd4 Nf3 Qxe4 tactically, as it prepares Re1! pinning and winning Black's queen. This leads to an endgame after 5...f6 6. d4 exd4 7. Nxd4 c5 8. Ne2 Qxd1 9. Rxd1=. Instead, Black can choose to keep queens on the board and play 5...Bg4 to pin the knight, where 6. h3 h5 reaches the Alapin gambit, and if White accepts the "free" bishop they find themselves regretting opening the h-file; or 5...Bd6 to defend the pawn and prevent the queens from seeing each other.

5. Nc3, the Keres variation, defends the pawn with a piece. This amounts to an endgame offer after e.g. 5...f6 (to defend e5) 6. d4 exd4 7. Nxd4 c5 8. Nde2 Qxd1+ 9. Nxd1=. 5...Bg4 holds no special power in this line because White has not castled yet, and 5...Bg4 6. h3 Bh5 7. g4 Bg6 8. Nxe5⩲ wins a pawn for White.

5. d4 immediately leads to an endgame after 5...exd4 6. Qxd4 Qxd4 7. Nxd4=.

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

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Bxc6 dxc6

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