Mozart’s piano sonata K 545 is a completely different illustration of a sonata, and is widely regarded as one of his easiest sonatas to perform. It is likely that he composed as a method of teaching. Mozart would compose pieces with deliberate structural functions and levels of difficulty in order to help students learn various techniques. K 545 is one of Mozart’s later works, and is categorised as a Viennese sonata.
The circle of fifths is an integral part to this sonata, further reinforcing the idea of the piece being a teaching tool. The first theme focuses on C major, being the tonic of the sonata. In the very beginning of this piece, we also see that recurring technique in Mozart’s sonatas; an Alberti bass line, which to an extent provides it with an aspect of similarity to the K 284. Also like the K 284, we see Mozart using deliberate juxtaposition to highlight sections of his work. He deliberately contrasts the triadic nature of the first theme by finishing it with scaling melodies, before returning to the arpeggios of the beginning.
From the C, Mozart continues the natural progression into the dominant, the G. Here, we see descending triads, again, a contrast to the earlier triads which were ascending. In the third variation, there is a lot more movement than typically would be, with Mozart incorporating full cycles of fifths, going all the way through and returning to the dominant key of G. In a way, like the change of dynamics within sonata K 284, the full circle of fifths adds a sense of momentum to the piece, especially with his added embellishments of grace notes. To again emphasize the importance of the dominant key of G, a codetta is added to the fourth section, within the exposition. Mozart further expands this codetta, by including the Melodic theme from the codetta in the following development. We can also see a sense of the cross-hand technique here, as used in the K 284 sonata too. There are scaling patterns on the treble line, and a much sparser section of notes on the bass line, however, we see this pattern alternating which small parts of scales appearing on the bass line, and singular notes and rests subsequently appearing on the treble line. This adds an interesting dynamic within the development; it could be argued this makes the sonata feel less formulaic, and less like it has been rigidly written solely for teaching; it reflects an idiosyncrasy of Mozart himself.
The development itself is relatively short, very unlike in K 284, wherein the development was long enough to be a sonata in its own right. This shows how Mozart has played with the standard idea of a sonata structure. The end of bars 29-34 features a perfect authentic cadence in the key of F, so we can see the roots of the notes providing the bass, with the tonic key providing the highest note within the final chord.
Arguably, the recapitulation is the most compelling section of the sonata, due to its ‘deviation’ from expectations of a typical recapitulation. The primary theme is generally in original key of the piece, however, here Mozart uses the subdominant key of F major to form his recapitulation. This is not merely a whimsical decision though; the deliberate alteration thus provides a sense of cohesion throughout the entire piece as it links the exposition to the recapitulation, not only through the employment of melodies, but also because the deviation from the standard arrangement creates a sense of organic progression, by using tonal centres that are located beside each other on the circle of fifths.