In Mouret's "Rondeau", above, the high instruments expand the initial D Major tonic by descending from F-sharp and A in the pick-up, through the passing tones (PT's) E and G and then resolving on D and F-sharp.
Passing tones (PT), as explained on page 1.5 are approached by a chord tone by step and then continue stepwise in the same direction to the next note. The illustration to the right shows a descending passing tone, though they may also ascend. As in the Mouret example at the top of the page, a passing tone often fills in the melodic interval of a third--which is itself often a consonant skip with no change of chord.
The video to the left shows two expanded fundamental harmonic progressions. The first one, in its most basic form, has scale degree 2 in the soprano as an embellishing tone upper neighbor. The second one has scale degree 7 as an embellishing tone lower neighbor.
In measure 1 an ascending passing tone expands the initial tonic. It fills in the third created by a consonant skip, D to F, in the D minor chord.
In measure 2 a descending passing tone expands the dominant. It fills in the third created by alto movement from scale degree 5 to 3 (recall from 1.4 the voice leading in which inner voices descend by third).
In the next-to-the-last measure a chromatic passing tone--a note outside of the key or scale--expands the dominant. This passing tone only fills in the melodic interval of a major second, from A to B.
