Modern Line

The Modern Line is the Slav Defense with 3. Nf3, White's traditional main move at this point. The knight develops toward the kingside and adds control of e5, while White postpones Nc3. That flexibility keeps open quieter setups with e3, and it changes how Black's natural third moves work.

Two replies that look natural are considered dubious. As against 3. Nc3, the immediate 3...Bf5 runs into 4. cxd5 cxd5 5. Qb3, when the double attack on b7 and d5 costs Black a pawn. Even so, it is the third most common reply in the database, and Black scores about as well with it as with the main moves. Taking on c4 also works less well than it does after 3. Nc3. Following 3...dxc4 4. e3, White prepares 5. a4 and recovers the pawn with the better game, because a knight on f3 cannot be harassed by ...b5-b4 the way one on c3 can.

Black therefore usually develops first. 3...Nf6 accounts for more than half of all games. After 4. Nc3 the play enters the central Slav position with its main branches, including the Semi-Slav if Black follows up with ...e6. White can also avoid that theory with 4. e3, the Quiet Variation, where Nc3 is delayed or left out. 3...e6 is the second most popular reply and generally transposes back into lines that arise after 3...Nf6, with a few independent exceptions. 3...a6 is a rare but solid alternative that normally reaches the main line of the Chebanenko Variation. Against it White can instead choose a Catalan-style setup with 4. g3.

Engines rate the position as roughly balanced, and the leading engine choices are 3...Nf6, 3...e6 and 3...dxc4. In online play White scores somewhat better than Black and draws are uncommon. The line is mainly a gateway to the main Slav and Semi-Slav positions rather than a variation with an independent character, so the play that follows depends largely on which of those systems the players choose.