The work is unified by the recurrence of two pitch pairs, namely Bb-C and B-Eb (referring to Betsy Campeau and her husband, Hank Smith), which are heard in various combinations and registral configurations throughout, usually as the opening and/or closing material of each movement.
Despite the fact that Postcards... is written for unaccompanied clarinet,
its conception is as much vertical/harmonic as it is linear/melodic. Polyphonic
melody abounds in the second and third movements, but implied harmonic
shifts occur in the outer movements as well, even the scales of the fourth.