Main Line (5.d4)

The idea

After 5.d4 d5 6.Bd3, White has a pawn on d4, a bishop eyeing the knight on e4, and is ready to castle. Black's knight on e4 is well supported by the pawn on d5 and is the heart of Black's position.

Black's main choices at move 6 are 6...Nc6 or 6...Be7 (the Jaenisch Variation, after White's c4) and 6...Bd6 (the Marshall Variation).

Plans for White

Castle, then hit the center with c4, attacking d5 and undermining the knight on e4. Re1 adds pressure on the e-file. White's goal is to make Black's well-placed knight a target.

Plans for Black

Develop with ...Nc6, ...Be7 or ...Bd6, and castle. When White plays c4, decide between keeping the tension and answering pressure on d5 actively, for example with ...Nb4 in the Jaenisch Variation.

Watch out for

For Black, leaving the knight on e4 without enough support. Once White plays c4 and the d5 pawn is exchanged, the knight can become loose and run out of squares.

For White, a premature attack. Black's position is sound, and an attack without enough pieces can leave weaknesses behind.