Mozart’s mature violin sonatas are twenty, from number 17, K. 296 to number 36, K. 547. Four of these are incomplete, including the final movement of K. 403 discussed below. They are remarkable indicators and expressions of essential mastery of music. I give two examples.
In sonata 19, in E flat major, K. 302 (Mannheim, 1778), the opening of the andante grazioso demonstrates how Mozart was able to instantly attract the attention of the ear, almost to the point of hypnosis. The theme begins with two dactylic bars of exactly the same note, E flat, stated on the first beat first at the octave and then at the double octave, and on the second beat a return to the single octave followed by a dissonance of E flat against D.
This leads, in the second bar, to the interval E flat and C, stated as a sixth, the C then dropping an octave, emulating the pattern of the first bar, and, on the second beat, a return to the interval of a sixth followed by the C dropping to B flat to produce an interval of the fourth stated as a fifth.Ama
The key is perfectly clear and the movement of the notes perfectly steady, but an astonishing shift of sound occurs in the space of four beats.
In sonata 30, in C major, K. 403 (Vienna, 1782), the opening of the allegro moderato demonstrates the same mastery. Here, Mozart employs, effectively, the antidactyl, or anapest. The key is perfectly clear from the opening chord, and again Mozart, to attract the ear, uses the drop of an octave in the piano; but here it is all essentially chordal, and the melodic line, instead of using a falling scale uses a rising one.
The feature that is remarkable is the insertion of a fast triplet on the second strong beat of the bar, the effect of which is to displace the impetus of the inherent rhythmic strength and, hence highlight, its displacement; and further, by having the triplet, which is also scalar, not begin a fourth below the note it is to come to, but to begin a third below, thus culminating on the same note it is to come to, it emphasizes not only its rhythmic displacement but also its restoration. The pattern is repeated a note higher, but with the bass unchanged, in the second bar, thus changing the harmony but not the pattern, producing an astonishing shift of sound in the space of two bars.