Early ...c5

The idea

After 3...c5 4.e3, Black has challenged d4 at once and prepares ...Qb6, hitting b2 and d4 together. This is a popular response at higher levels, aimed at White's queenside.

Plans for White

Keep d4 solid with c3, and be ready to meet ...Qb6 with Qb3 or Nc3. Developing quickly and castling lets White ignore some of the pressure. Nbd2 and Bd3 keep the usual London setup.

Plans for Black

Bring the queen to b6 and the knight to c6, and decide between keeping the tension on d4 or gaining space with ...c4. The queen on b6 ties White's pieces to defending b2.

Watch out for

For White, b2. After ...Qb6, the b2 pawn is attacked, and the bishop on f4 can't come back to defend it.

For Black, taking on b2 at the wrong moment. A queen on b2 can come under attack from White's rooks and knights, so count the dangers before grabbing.