this system often leads to isolated queen's pawn (iqp) positions. white gains rapid development, a grip on e5, and kingside attacking chances to make up for the long-term weakness of the isolated d4 pawn. the common continuation in this line is 4...nf6 5.nc3 e6 6.nf3. black's main alternatives are 6...bb4 (a position which often transposes into lines of the nimzo-indian defence) and 6...be7. 6...nc6?! is not as good because of 7.c5!, and white plans on controlling the e5-square through the advance of his b-pawn to b5, or by exchanging black's knight on c6 after bb5.