A piece of music does not have to be a variation on a theme to follow the same principle - the decoration of a series of notes that are more structurally important.

There are no hard and fast rules for working out which notes are structural except that they must be at the beginning or end of the diminution and MUST be consonant with the harmonic unit (I, IV etc) being prolonged.

You may think that all Schenker is doing is giving obvious features complicated names. You do not need Schenkerian analysis to tell you, for example that the second half of the first bar spans a fifth.

Schenker suggests, however, that connecting C and G in this way, the composer binds these two notes, and all those in between into a musical unit. His revelation is that if you strip away this first layer of diminutions you find that you are left with a new layer of diminutions hidden below the surface of the music.

A good illustration of this is the last five bars of the example above - from the G in bar 4 to the C bar 8 the notes picked out by upwards stems describe a descending fifth progression.