A study of the general tonality of a music piece through the various modulations and key changes. For this, let's take the previous "Lied" structure with three parts ABA'. In the Part A of the exposition, the thematic element a1 begins in the key F# minor (main key), then makes a short modulation in the key of A major and ends in G major, the tone of the Neapolitan sixth, placed on the lowered second degree of F# minor. The second degree is G#, a semitone lower in order to obtain the G natural. The second element a2 also begins in F# minor and concludes in the key of G major also. The following bridge also begins in the home key of F# minor, and gradually move towards the key of A major, in order to prepare the second part B or the second theme in A major or in the relative key : F# minor. The theme B is exposed in A major, and the following transition will also be in A major, going gradually towards the main key of F# minor, in order to introduce the third part A' or (variation of A) in the recapitulation. The first thematic element a1 reproduces the same tonal progression as in the exposition. The second element a2 reiterates the tonal progresion of the exposition. The a'2 element, which is an ornamented comment of the element a2 on piano solo, but this time in the main key of F# minor. A short transition follows, using the same tonality as in Part B: F# minor and G major. The final conclusion or coda, remains in the key of F# minor. The tonal progression is relatively simple, since it remains in the main key of F# minor (Theme A), the relative key (A major / Theme B), before returning to F# minor, in the recapitulation.