Mozart: Piano Sonata No.17 in B-flat major, K.570 Analysis


First Movement (Allegro)

Form: Sonata Form. B flat major

Mozart Piano Sonata No.17 in Bb major, K.570 Analysis 1


Bars 1-20: First Subject in Tonic. The first subject consists of two sentences, each ending with a full close in the tonic. The construction of Bars 4-12, should be carefully noted. The eight bars contain the responsive phrase of the opening sentence, and its cadential repetition. Instead, however, of dividing equally into a normal four-bar phrase, and its repetition of similar length, the phrase is first contracted to three bars, and then, on repetition, is lengthened to five bars by slight extensions both at the commencement, and at the close.

Bars 21-40: Passage of Transition. The principle portion of the transition is of very melodious character. It starts with two introductory bars in G minor, after which a melodious four-bar phrase in E flat major enters. This is immediately repeated and extended, modulating to F major (the key of the dominant) through C minor and B flat major, and again momentarily through C major, back to F. The concluding bars of the passage are more characteristic of the transition of the period.

Bars 41-69: Second Subject in F major (Dominant). It is of interest to note that the opening phrases of the subject are formed by a combination of the first motive of the first subject with a second motive, which is derived from the second motive of the same subject. These, transposed of course, into the key of the second subject, are now heard together instead of consecutively. In Bars 45-48, the opening phrase of the subject is repeated on the chord of the diminished triad.

Bars 70-79: Codetta. The codetta consists of a four-bar phrase, repeated cadentially with slight modification and extension.

Double bar and repeat.


Bars 80-132: The development opens with an almost literal, though somewhat lengthened, transposition of the transitional passage. Commencing in the key of D flat major, it modulates through B flat minor, F minor, and C minor, to G minor, on a half-cadence in which key the first portion of the development closes. The remainder of the section is worked on the opening phrase of the second subject – first, on the entire phrase, but, after Bar 116, the bold arpeggio figure is dropped, and the remainder of the passage is worked on the quaver (eighth note) figure alone. In Bars 101-104, the phrase is taken on the tonic chord in G minor, modulating, in the last bar, to C minor, on the dominant seventh in which key the phrase is repeated, in Bars 105-108. In Bars 109-117, the foregoing eight bars are repeated with the parts inverted, this time, however, on the tonic chord in C minor, and the dominant seventh in F minor. Bars 117-122 form a descending sequence, modulating through E flat major and C minor. In Bar 125, the parts are again inverted, the music modulating to B flat minor. The development ends, after yet another re-inversion of the parts, on the dominant seventh in B flat major.


Bars 133-152: First Subject in Tonic.

Bars 153-170: Passage of Transition. The transition reappears modified so as to end in the key of the tonic.

Bars 171-199: Second Subject in Tonic.

Bars 200-209: Codetta.

Double bar and repeat.

Second Movement (Adagio)

Form: Old Rondo Form. E flat major.

Mozart Piano Sonata No.17 in Bb major, K.570 Analysis 2

The “time” of the movement is really two crotchets (quarter notes) to the bar, and not four, as is actually written. The position of the cadences proves this; and now written, they invariably fall in the weaker half of the particular measures in which they occur, whereas, if the movement is rewritten with the shorter measures not only will the cadences all fall naturally and regularly in the more strongly accented of the measures, but, in by far the greater number, the cadence-chord will also fall on the strong accent. Moreover, when re-written as above, the sentences throughout the movement will prove to be of the normal eight-bar length, all regularly dividing into two four-bar phrases.

Bars 1-12: Principle Subject (in Tonic) first entry. Ternary Form.

  • Part i: Melody in E flat major (Bars 1-4). Double bar and repeat.
  • Part ii: Four bars containing slight digression (Bars 5-8).
  • Part iii: Repetition of Part i (Bars 9-12). Double bar and repeat.

Bars 13-28: Episode I in C minor (Relative minor). Ternary Form.

  • Part i: New melody in C minor, modulating to G minor followed by a repetition written out in full (Bars 13-20). Double bar.
  • Part ii: Modulating, sequential passage leading to Part iii (Bars 21-24).
  • Part iii: Repetition of Part i, modified so as to close with gull cadence in C minor (Bars 25-28). Double bar and repeat.

Bars 28-31: Link, modulating and leading to the Principle Subject

Bars 32-35: Principle Subject in Tonic (second entry), partial reappearance only. 

Double bar.

Bars 36-47: Episode II, in A flat major (Subdominant). Binary Form.

  • Part i: Melody in A flat major, modulating to E flat major, followed by a repetition written out in full (Bars 36-43). Double bar.
  • Part ii: Melody, modulating back to A flat major (Bars 44-47). Double bar and repeat.

Bars 48-51: Link, modulating and leading to Principle Subject.

Bars 52-55: Principle Subject (in Tonic), third entry, partial reappearance only.

Bars 56-63: Coda. The coda is founded on the episodes.

Third Movement (Allegretto)

Form: Episodical Form. B flat major.Mozart Piano Sonata No.17 in Bb major, K.570 Analysis 3

This is the only instance in these sonatas in which Mozart has chosen episodical form for the finale.

PART I – Principle Subject (Bars 1-22):

Bars 1-8: Part i: Melody in B flat major.

Bars 8-14: Part ii: Passage in F major (Dominant).

Bars 15-22: Part iii: Repetition of Part i (exact).

Double bar.

PART II – Episode (Bars 22-56):

Bars 22-42: Section i, in B flat major (Tonic).

  • Part i: Melody in B flat major, modulating and ending in F major (Dominant) (Bars 22-30). The opening bars are written on a tonic pedal. Bars 27-28, in the keys of G minor and F major, respectively, are of sequential character. Double bar and repeat.
  • Part ii: Passage starting in C minor, and modulating through B flat minor to F major (Dominant) (Bars 30-34). Bars 31-32, in C minor, modulating to B flat minor, are founded on the principle motive in the preceding melody, and form a short sequence.
  • Part iii: Repetition of Part i, modified to end in the key of the tonic (Bars 34-42). Double bar and repeat.

Bars 42-44: Link. The link, starting in Bar 42, is founded on a little figure form the principle subject (Bars 4-5)

Bars 45-56: Section ii, in E flat major (key of the Sumdominant).

  • Part i: Melody in E flat major, modulating to B flat major (Dominant) (Bars 45-48). Double bar and repeat.
  • Part ii: Modulating passage founded on figures from the preceding sentence (Bars 49-52). Part ii opens in the bass with the repeated note figure with which Part i commenced in the treble, but taken by inverse movement; and Bars 51-52 are an inversion of Bars 47-48, the intervals in the treble of Bar 51, being also taken by inverse movement.
  • Part iii: Repetition of Part i, modified to close in E flat major (Bars 53-56). Double bar and repeat.

Bars 57-62: Link. The opening bars of the second link are founded on the chromatic scale-passage, first heard in Bar 47. The passage is first taken in the bass, and then, with the parts inverted, it is imitated a seventh higher in the treble. The closing bars are a repetition of a passage from Part ii of the principle subject (Bars 12-14).


Bars 63-70: Repetition of portion of Part I (eight bars only).

Bars 70-89: Coda. The coda is founded on passages from both sections of the episode. Bars 74-78, are repeated in Bars 78-82, with the parts inverted and varied.