Four Knights System, Nimzowitsch Variation

The Nimzowitsch Variation arises when White, instead of the usual kingside fianchetto with g3 and Bg2, answers the symmetrical knight development of the English Four Knights with 4. e4. The pawns on c4 and e4 give firm control of d5, but the d-pawn stays behind, d4 becomes a hole, and the knights on c3 and f3 are left to hold the center. Black is not obliged to defend anything at once and can develop actively, aiming at the dark squares and at White's slightly loosened kingside.

The most frequent reply is 4...Bc5, placing the bishop on the a7–g1 diagonal toward f2 and the weakened d4 square. Nearly as common is 4...Bb4, which pins the c3 knight and increases pressure on e4, with a later ...Bxc3 able to leave White with doubled c-pawns. The quieter 4...d6 supports e5 and keeps a compact setup. The engine rates the position as roughly balanced, and in online games results are close to even, with White scoring slightly better.