Classical Variation, 4. Bg5

4. Bg5 is White's main alternative to 4. e5 against the Classical French. It brings a piece into play before the center is fixed. The pin turns 5. e5 into a real threat, since the knight could no longer retreat without losing the queen. Black has three main answers. More than half of games continue 4...Be7, the Normal Variation, which removes the pin and accepts the closed center after 5. e5 Nfd7. That line was long the main line of the whole French. The second answer is 4...dxe4, the Burn Variation, played in about a quarter of games. It dissolves the tension and avoids e5 altogether, producing Rubinstein-like positions in which Black often gains the bishop pair. At the top level it has overtaken 4...Be7. The third answer, 4...Bb4, is the McCutcheon Variation. It ignores the threat and pins the c3-knight in return, and it leads to the sharpest play.

Kicking the bishop with ...h6 and ...g5 is a further way to break the pin, but it loosens Black's kingside. The engine rates the position as roughly balanced. On Lichess White scores slightly better overall, but Black edges the results in the McCutcheon.