Certain musical works, Bach's famous Chaconne being an example, have a structure in which intense passages come in more or less widely separated waves, like a series of rapids in a waterway. The energy of the work seems to be contained in these portions of it and calmer sections between them could be heard as re-groupings in which frayed ribbons of sound are knit back together so as to gather the momentum for another descent. With more familiarity you are able to perceive the rippling and overlapping forms in these quieter interludes and to realise that the greater interest of the work lies in them. The descending portions are causal, while these delve into the energies that are prior to cause.