The "Pure" Slav and a6 Slav address these problems. Black's queen bishop is unblocked; the pawn structure remains balanced. Also, if Black later takes the gambit pawn with ...dxc4, the support provided by the pawn on c6 (and possibly ...a6) allows ...b5 which may threaten to keep the pawn, or drive away a white piece that has captured it, gaining Black a tempo for queenside expansion. On the other hand, Black usually will not be able to develop the queen bishop without first giving up the center with ...dxc4, developing the bishop may leave the black queenside weak, and the thematic break ...c5 incurs the loss of a tempo.