Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...Bc5/4. c3

4. c3, the Central variation, is the most critical move to the Classical defence in the Spanish game. c3 supports White playing d4, building a big pawn centre and kicking Black's bishop.

In addition, White is now threatening to win the e5 pawn. This is because the c3 pawn takes away the d4 square that Black required to defend the pawn tactically. Now if, say, 4...a6? 5. Bxc6 dxc6 6. Nxe5, Black doesn't have the riposte ...Qd4 to win the pawn back/threaten ...Qxf2#. Black's best attempt is 6...Qe7 7. d4 (kicking the bishop and defending the knight) Bd6 8. O-O (allowing Black to win back the pawn in exchange for development)⩲.

4...Nf6 is the most common response. This invites 5. d4, attacking the bishop; or White can castle 5. O-O transposing into the Zukertort gambit.

4...d6? is a common amateur reply, but a mistake. Black pins their own knight, and by preventing the retreat of Black's bishop, it is easy for it to become trapped after 5. d4. (e.g. 5...exd4 6. cxd4 Bb4+ 7. Kf1! Bd7 8. Qa4 a5 9. a3 and Black's bishop is trapped. Or if 5...Bb6 6. d5 Black is losing a knight.)

4...f5!? is the Cordel gambit. Black attacks the e4 pawn, though this isn't as sharp as 3...f5, the Schliemann.

4...d5!? is the Konikowski Gambit.

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

1. e4 e5 2. Nf3 Nc6 3. Bb5 Bc5 4. c3

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