Beethoven's new order

The facts of thematic life are that every manifestation of a theme tends to divide into two parts. This is irrespective of whatever tonality is employed. In the West, even the simplest diatonic melody (that is one which we perceive to be in a tonality derived from major and minor scales) does this. For example there is a ‘natural’ tendency to gravitate between one note (the tonic) and another note a fifth higher or a fourth lower (the dominant); but such a modulation is not necessary to qualify part of a theme as a different phrase in the musical sentence; there may simply be a moment where the music pauses, reaching a recognisable point before moving to another independent fragment. Moreover, in sophisticated examples of bipartite form, such as the sonatas of Domenico Scarlatti, the duality is engendered not so much by a single theme as by an ensemble of aspects to the initial material, which in their turn form a group by themselves - a section - and where the borders between such sections are not always clearly definable.