5. Mozart, Sonata in A minor.
6. Hummel, 'Pianoforte School.'
7. Bach, 'Passionsmusik.'
8. Beethoven, 'Adelaide.'
Exceptions to the above rules are met with as follows:—to the first and second rules in Bach and Mozart, who frequently employed an appoggiatura (called by Marpurg 'der kürzeste Vorhalt') which was worth one third or less of the principal note, but which differed from the short appoggiatura in being accented (Ex. 9). An exception to the second rule occurs whenever its strict observance would occasion a fault in the harmonic progression (Ex. 10), or when it would interfere with the rhythmic regularity of the passage (Ex. 11). Exceptions to the third rule are of still more frequent occurrence; many passages containing a tied note preceded by an appoggiatura would entirely lose their significance if the rule were strictly adhered to. Taste and experience alone can decide where similar exceptions are admissible.
In the works of some of the earlier composers an appoggiatura is occasionally, though very rarely, to be met with, which although placed before a note capable of being halved, yet receives three-fourths of its value. This appoggiatura was usually dotted (Ex. 12).
9. Bach, 'Passionsmusik.'
Mozart, Fantasia in C minor.
10. Bach, 'Suites Françaises.'
11. Schubert, Rondo, Pianoforte and Violin.
The appoggiatura, whether long or short, is always included in the value of the principal note; if therefore it is applied to a chord it delays only the note to which it belongs, the other notes of the chord being played with it (Ex. 13).
13. Beethoven, Andante in F.
Mozart, Sonata in F.
The manner of writing the appoggiatura bears no very definite relation to its performance, and its appearance is unfortunately no sure guide as to its length. In music of the 17th century, at