The common accented nonharmonic tones are the accented passing tone, accented neighboring tone, suspension (occurs only as an accented nonharmonic tone), retardation, and appoggiatura.
The suspension is one of the time-honored methods of bringing variety and interest to a harmony. The principle of the suspension is that a note belonging to the previous chord is held over into the next chord, with which it forms a dissonance. This creates a powerful moment of tension, which is then released when the suspension falls stepwise to the harmony note. As treated conventionally, a suspension has three phases, which are called preparation (i), suspension (ii), and resolution (iii).
The suspended tone (the middle tone of the figure) is always dissonant. Suspensions are designated by the interval forming the suspended tone and resolution with the lowest sounding voice. Another common suspension is the 2–3 suspension
The other voice (not containing the suspension figure) may move in almost any way as long as it provides the necessary preparation, suspension, and resolution phases for the suspension figure.
Suspensions are typically applied to the intervals of the fourth, also called a 4–3, seventh, also called a 7–6, and ninth, called a 9–8.
A favorite technique of classical composers was to introduce a chain of suspensions, which would often culminate upon the dominant chord of a new key.
Suspensions can occur simultaneously in pairs (a), have decorated resolutions (b), occur in chains (c), or be accompanied by a changing bass line (d).
A retardation is a nonharmonic tone similar to a suspension, except that the resolution is upward instead of downward. Retardations tend to work best when applied to the intervals of seventh and the ninth.
The appoggiatura is a nonharmonic tone that is approached by skip and resolved by step in the opposite direction. It generally occurs as an accented nonharmonic tone. As a decoration it behaves just like a regular passing note—that is, it moves stepwise up or down to the harmony note.
Haydn: Sonata in A Major, Hob. XVI:30, II: Var. 1, mm. 14–16.