Fundamental to Harris's expressive aesthetic is the concept of an emotional "arc": a work in progress, whether programmatic or abstract in character, was often sketched verbally, prior to any notes being set down, in terms of strong musico-dramatic qualities, which were to be realized through his idiosyncratic treatment of harmonic color coupled with varying levels of rhythmic activity and changes of register. A common manifestation of this concept is one in which the music starts in a low register in slow tempo with dark harmonic hue, moves with increasing animation and brighter harmony to an affirmative climax in a high register, then subsides to an emotional state reminiscent of the opening. Characteristic examples are the second movements of the Sonata for Violin and Piano and Symphony No. 5 (the middle portion of the movement). Only rarely, as in Symphony No. 11, is this curve inverted. Sometimes, he was only concerned with the ascending segment of the arc, as illustrated by the gradual upward surge of I. of Symphony No. 6 and the entirety of Fruit of Gold. This latter manifestation, which, perhaps more than any other aspect of Harris's art, conveys the visionary quality often associated with it, is usually meant to convey a pantheistic efflorescence, an "awakening" of natural surroundings that hearkens back to potent experiences of the composer's rural childhood. He also adapted his arc to a kind of "modular" design through the abrupt juxtaposition of what he called a "dream world" and an "action world." Sometimes these states are embodied in two correspondingly distinct movements of a larger work, as in American Creed, Soliloquy and Dance, and Elegy and Dance; in other instances the juxtaposition occurs between sections of a single-movement piece, as in Ad Majorem Gloriam.
Harris's style is an amalgamation of diverse elements. His melodies owe in their contours, modal characteristics, and flexibility of phrase structure a debt to both monophonic chant and the lines of Renaissance vocal polyphony. They also reveal a kinship with Anglo-American folk music and early Protestant hymnody. Underlying the melodies is what he somewhat misleadingly called a "polytonal" adaptation of the old church modes; in this, melodic phrases are based on a combination of two different modes built on the same tonic, a situation that produces inflections on various scale degrees and a sense of constantly shifting octave-species.
