With ...c6 Black supports d5 and keeps the c8–h3 diagonal open, so the light-squared bishop can come out before ...e6.
Key principles
- Develop the bishop to f5 or g4 before ...e6
- The Semi-Slav adds ...e6 and keeps flexible pawn breaks
- ...dxc4 followed by ...b5 is a typical Slav idea
Common mistakes
- Playing ...e6 first and shutting the bishop in
- Grabbing on c4 without a plan to hold it