Symmetrical Variation, Full Symmetry Line

The Full Symmetry Line is the position in which both sides have developed both knights and fianchettoed the king's bishop, with only the c-pawns advanced. ECO classifies it as A38 and gives it via 1. c4 c5 2. Nc3 Nc6 3. g3 g6 4. Bg2 Bg7 5. Nf3 Nf6. The order shown here, beginning 1. c4 Nf6 2. Nf3 c5, reaches the same position, and the position after 2. Nf3 can also come from the Zukertort Opening with 1. Nf3 Nf6 2. c4. Every Black piece mirrors its White counterpart, so the game turns on how and when White uses the move in hand to break the symmetry, usually with a d-pawn advance.

Castling with 6. O-O is by far the most popular choice and keeps White's options open. After 6...O-O 7. d4 the game enters the Mecking Variation (A39), White's most direct attempt to open the center. The immediate 6. d4 pursues that idea at once and scores slightly better for White in the database, while 6. d3 prepares a slower buildup. The engine gives White a slight edge, and White scores somewhat better than Black in practice. Draws are uncommon in online play.