Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. Nc3

3. Nc3 is White's most popular move against the French at the top level, and is considered the most challenging option. White develops a piece and defends the e4 pawn. In contrast to the 3. Nd2, the second most common line, this also pressures d5 and keeps the c1-h6 diagonal for the queen's bishop to develop.

Black has two main options, both of which leave the tension between d5 and e4 and develop a piece.

3...Nf6 is the classical approach. The main continuations are 4. e5, the Steinitz variation, leading to 4...Nfd7 5. f4 c5 6. Nf3 Nc6 7. Be3⩲; and 4. Bg5, after which 4...dxe4, 4...Be7, and 4...Bb4 are all played.

3...Bb4, the Winawer variation, is the chief competitor to 3...Nf6. This pins the defender of e4 and so elicits 4. e5, closing the position. Black intends to trade off their "good bishop" for White's knight: 4....c5 5. a3 Bxc3+ 6. bxc3⩲.

Together, these two moves make up about 90% of the continuations.

The most important of the sidelines is 3...dxe4, the Rubinstein variation. The purpose of this move is to meet both of White's most common turn three options, 3. Nc3 and 3. Nd2, the same way. The two positions transpose after 4. Nxe4.

Other "also-rans" include:

• 3...Nc6, the Hecht-Reefschläger variation, which prevents Black from playing ...c5, which is usually a key resource in the French.
• 3...c5?!, the (dubious) Marshall gambit, where Black plays ...c5 too early! Usually Black waits until after e5 has been played before attacking the centre with the c-pawn. By attacking before e5 has been played, Black lets White play 4. exd5 exd5 5. dxc5 Bxc5 6. Qxd5±, and Black is simply a pawn down.

Louis Paulsen (1833―1891) first played 2. Nc3 in his match against Baron Ignatz von Kolish, London 1861. Kolish tried both 3...Bb4 and 3...dxe4.^[1][2][3]

Heyde, in his 1891 treatise on the French, appraised it as being White's best and most interesting line, and it remains the top choice among GMs in tournaments today.^[4] Heyde recommended 3...Nf6 over 3...Bb4. 3...Bb4's critical reappraisal would come in the 1920s where Aron Nimzowitsch and later Mikhail Botvinnik introduced new ideas in the line.^[5][6]

1. e4 e6 2. d4 d5 3. Nc3

Wikipedia has related information at French Defence.