In European classical music, "[t]he greater use of dissonance from period to period as a result of the dialectic of linear/vertical forces led to gradual normalization of ninth, eleventh, and thirteenth chords [in analysis and theory]; each additional non-chord tone above the foundational triad became frozen into the chordal mass.
Augmented and diminished intervals are also considered dissonant, and all nonharmonic tones are measured from the bass note, or lowest note sounding in the chord except in the case of nonharmonic bass tones.
The most important distinction is whether they occur on a strong or weak beat and are thus either accented or unaccented nonchord tones.
An anticipation (ANT) occurs when this note is approached by step and then remains the same.
A portamento is the late Renaissance precursor to the anticipation,[5] though today it refers to a glissando.
[6] The German term Nebennote is a somewhat broader category, including all nonchord tones approached from the main note by step.
Endeavor, moreover, to introduce suspensions now in this voice, now in that, for it is incredible how much grace the melody acquires by this means.
If a tied note is prepared like a suspension but resolves upwards, it is called a retardation.
Decorated suspensions are common and consist of portamentos or double eighth notes, the second being a lower neighbor tone.
A chain of suspensions constitutes the fourth species of counterpoint; an example may be found in the second movement of Corelli's Christmas Concerto.
[11] An example of a nonharmonic bass from the third movement of Stravinsky's Symphony of Psalms.
[13] The example below shows chromatic nonharmonic tones (in red) in the first four measures of Chopin's Prelude No.