Czech Variation, Classical System

The Classical System is the most common answer to the Czech Variation, and Wikibooks also calls it the Dutch Variation. With 6. e3 White frees the light-squared bishop to win back the pawn on c4. The cost is that the c1-bishop is shut in for a while; White plans to release it later with the e4 advance. Black almost always replies 6...e6, completing the light-square setup with the bishop already outside the pawn chain and preparing ...Bb4. That square became available once 5. a4 gave up control of b4 to stop ...b5.

The main line runs 7. Bxc4 Bb4 8. O-O O-O 9. Qe2. White has castled and recovered the pawn, and the queen move supports the coming e4 break. Black uses the pin on the c3-knight and the active f5-bishop to contest that advance. 6...Nbd7 is a much rarer alternative. 6...Na6, the Lasker Variation, sends the knight toward b4 in place of the dark-squared bishop. Engines give White a slight edge, and in online games White scores a little better than Black.