Key ideas
- 5.Nf3 is the main move. The Classical Line, 5...Be7 6.O-O O-O 7.Qc2 a6 8.Qxc4 b5 9.Qc2 Bb7, returns the pawn but gains time against the queen and puts the bishop on b7 to challenge the g2 bishop.
- 5...Nc6 6.Qa4 Bb4+ is the Modern Sharp Variation. Black keeps the extra pawn for a while and develops with checks and pins, and White must work to win it back.
- 5.Qa4+ Nbd7 6.Qxc4 regains the pawn at once. After 6...a6 7.Qc2 (the Alekhine Variation), Black aims for ...c5 or ...b5 and ...Bb7.
- Once the pawn is back, White has a central pawn on d4 against Black's e6 pawn and pressure along the long diagonal. Black's ...c5 break dissolves White's centre and is the main equaliser.
Plans for White
Recover the pawn without losing time, usually with Qc2 or Qa4 and Qxc4, then use the g2 bishop and the c-file against Black's queenside. If Black weakens it with ...a6 and ...b5, a4 hits the pawn chain.
Plans for Black
Either give the pawn back cleanly and use the time for ...a6, ...b5, ...Bb7 and ...c5, or hold it with ...a6 and ...b5 and accept some risk on the long diagonal. Once the c8 bishop reaches b7 and ...c5 is achieved, the opening has done its job.
For the wider picture, see the Catalan Opening guide.