Main Line (3.Bd3 e6 4.Nf3 c5)

The idea

After 3.Bd3 e6 4.Nf3 c5 5.c3, White keeps a strong pawn pair on d4 and e4, backed by c3. MCO-15 rates the position as clearly better for White, and Lawrence Trent writes that 4...c5 has been almost refuted by cloud engines, suggesting 4...d5 instead.

Plans for White

Castle, develop with Nbd2 or Qe2, and keep the center. With the pawn on c3, d4 stays strong after ...cxd4 cxd4, and White can gain more space with d5 or e5 at the right moment.

Plans for Black

Play ...cxd4 at a good moment, develop with ...Nf6, ...Be7 and ...Nc6, and keep hitting e4. Black wants to open the long diagonal so the bishop on b7 counts. John Shaw suggests 5.Nc3 may be even stronger for White than 5.c3.

Watch out for

For Black, the d5 advance. If White plays d5 at the right moment, the bishop on b7 is shut out and Black is cramped.

For White, the bishop on d3. It defends e4 but can be traded by ...Nc6-b4 or ...Ba6 ideas, which loosens White's grip on the light squares.