Nonharmonic tones (or non-chord tones) are notes that do not belong in a certain chord.
In this example, the F is a nonharmonic tone because it does not fit into the I chord (which contains C, E, and G).
Before discussing the different types of nonharmonic tones, we need to define two terms:
A step is equal to an interval of a generic second.
A skip is equal to an interval of a generic third or more.
A passing tone (PT) is approached by step and then continues by step in the same direction.
If a passing tone occurs with the second chord (instead of in the middle of the two chords), it is called an accented passing tone (>PT).
A neighboring tone (NT) is approached by step and then returns by step to the original note.
If it occurs with the second chord, it is called an accented neighboring tone (>NT).
An anticipation (Ant.) is approached by step and then remains the same. It is basically a note of the second chord played early. Anticipations are not accented.
An escape tone (ET) is approached by step and then skips in the opposite direction.Escape tones are not accented -- they occur in between the two chords.
An appoggiatura (App.) is approached by skip and then steps in the opposite direction. Appoggiaturas are accented -- they occur with the second chord.
A suspension (Sus.) keeps a note the same and then steps downward.
A retardation (Ret.) keeps a note the same and then steps upward. Both the retardation and suspension are accented.
Finally, changing tones (CT) use two nonharmonic tones in succession.
The first nonharmonic tone is approached by step and then skips in the opposite direction to the second nonharmonic tone.
The second nonharmonic tone then resolves by step.
They are sometimes called double neighboring tones or a neighbor group.
While the named non-harmonic tones discussed in this lesson are the most common, composers may choose to use others.