Rubinstein System

The Rubinstein System, 4. e3, is named after Akiba Rubinstein and covers ECO codes E40 to E59. White does not treat ...Bxc3 as an immediate threat and does not spend a tempo on 4. a3 to provoke it. Instead the e-pawn frees the light-squared bishop, which usually goes to d3 to help control e4. The main decision is where the king's knight goes. With Nf3 White accepts doubled pawns after ...Bxc3. With Ne2 White can recapture on c3 with the knight. Because the Nf3 main lines have held up well for Black, White has turned to Ne2 more often since the 1980s.

Black's most common reply is 4...O-O, a useful and noncommittal move. 4...c5 attacks the center at once. White cannot take on c5, since ...Bxc3 and bxc3 would leave tripled isolated pawns, so White keeps the tension. 4...b6, the St. Petersburg Variation, prepares ...Bb7, though ...Ba6 remains possible. 4...Bxc3+ is also frequent, and 4...Nc6 is the Taimanov Variation. The line 4...c5 5. Ne2 is the Rubinstein Variation, which is why 4. e3 is called a system. The engine rates the position as roughly balanced.