QUOTE(denmark77 @ Aug 4 2008, 10:09 AM)

Passing notes however, can involve an (almost) unlimited number of non-harmony notes between the two harmony notes, and can involve chromatic notes too - i.e. be a semitone apart from each other. For example, D Eb E F F#
Changing notes are not my forte, so I will pass on those...!
Changing notes = the upper and lower auxiliary notes heard one after another, e.g. the melodic segment C-D-B-C and C-B-D-C sounding over a C major or C minor triad
Correction to denmark77's definition of passing notes: The number of passing tones between two harmony notes
cannot be unlimited, if chords are built from stacked thirds and if the semitone is the smallest pitch subdivision.
In tonal music, it is common to find a single passing note or two passing notes between two chord tones, e.g. C-D-E over a C major chord, and D-Eb-F-G over a G minor chord.
Incidentally, in North America, most people refer to passing note as "passing tone", which can be either accented or unaccented; two passing tones in a row as "double passing tones"; auxiliary note as "neighbor tone"; and changing notes as "double neighbors".