Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nf3/3...Nf6/4. Nc3/4...a6

The move 4...a6 introduces the Chebanenko (or Chameleon) Slav. Though it seems a small move, it prepares ideas of ...b5 (either to attack White's c4 pawn or to shore up Black's after ...dxc4) and eases the problems of developing Black's light-squared bishop, as now Qb3 can be met with ...Ra7.^[1]

The weakening of the b6 square, however, invites White to simply push - 5. c5 is the most common response, gaining space on the queenside. In the resulting positions, it is very common for Black to fianchetto the dark-squared bishop, where it is a lot more useful by eyeing White's center.

Alternatively, White can play 5. e3, solidifying their d pawn and adding their light-squared bishop to the fight, while accepting 5...b5. Less common are 5. a4, preventing ...b5, and 5. cxd5, releasing the central tension but leaving Black to show what purpose ...a6 now serves.

The Chebanenko Slav is named after Vyacheslav Chebanenko, a chess theoretician and mentor who developed the system in the 1970s after facing it against Fyodor Skripchenko^[2][3].

1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 a6