King's English Variation, Four Knights Variation, Quiet Line

With 4. e3, White adds a pawn to d4 instead of fianchettoing. The move closes off the d4 square to a black knight and prepares a later d2-d4 that challenges e5. It also opens the f1-bishop's path toward e2 or d3. The structure resembles a Sicilian with ...e6 reversed, with White a tempo up. In the parent position this is the second most popular choice after 4. g3, and it leads to a calmer game with less theory than the fianchetto lines.

Black's most frequent reply is 4...Bb4, pinning the c3-knight and keeping open the option of capturing on c3 to double White's pawns. The next most common is 4...d5, which opens the center at once. 4...Bc5 aims the bishop at the kingside, but the e3-pawn blunts that diagonal, and White scores noticeably better against it than against the other two replies. The engine considers the position balanced and also rates 4...Be7 highly. In practice White wins slightly more often than Black, and draws are rare.