2.c4 offers a wing pawn for central control. In the QGA Black takes it and gives up the centre for a while; in the QGD Black holds d5 with ...e6.
Key principles
- In the QGA White usually regains c4 with e3 and Bxc4
- In the QGD Black's problem piece is the light-squared bishop
- Tension on d5 favours the side that keeps its pieces active
Common mistakes
- Trying to keep the c4 pawn with ...b5 in the QGA
- Releasing the tension with cxd5 at the wrong moment