Black offers White the possibility of 4.cxd5, which may be followed by 4...Nxd5 and 5.e4, giving White an imposing central pawn duo. If White does not take the d5-pawn, Black may eventually play ...dxc4, when a White response of e4 again leads to the same pawn structure. In classical opening theory this imposing pawn centre was held to give White a large advantage, but the hypermodern school, which was coming to the fore in the 1920s, held that a large pawn centre could be a liability rather than an asset. The Grünfeld is therefore a key hypermodern opening, showing in stark terms how a large pawn centre can either be a powerful battering ram or a target for attack.