The “form” of this movement is probably one of those experiments in structure which Bach worked out and perfected for himself. The harmonic centres – as shewn at the various Periods – are very clearly indicated and systematically distributed; great uniformity is observable in the thematic material, and the subject-matter is introduced in clear identity with the opening at those particular points where the indication of the commencement of a new key block is required. The power of every chord as a unit in the great tonal centre for the time being is carefully considered, and its force of curve to the side or to that fully adjusted. The ground used for action is first effectively staked out by the great harmonic bases, and every chord within this area is made to pull its proportioned weight up to its ultimate goal. The coherence, consistency, and unification of the whole is never lost sight of, and – though quite out of the bounds or suggestions of Sonata form – a more perfect picture it is impossible to imagine.