Choral compositions form a large and important part of his oeuvre. Some of the more ambitious early efforts have been criticized as being too instrumental in concept and demonstrating awkward prosody and insensitivity to effective representation of the text. But many of the smaller pieces, such as The Birds' Courting Song, He's Gone Away, Sanctus, and Year That Trembled, reveal a maturing idiomatic character and a practicality gained from his experiences in writing for both amateur and professional groups, especially during the 1940s. His most impressive a cappella work is the Symphony for Voices on words by Whitman, while of the accompanied efforts, the Folksong Symphony ranks as one of his finest compositions altogether, revealing great technical skill and colorful variety in its treatment of folktunes of diverse regional and ethnic characteristics. Although his achievements in this area are undoubtedly uneven, Harris may be regarded as one of the pioneers in the development of a literature of serious choral music in the United States.
There are also a very few songs, most of them exquisitely honed and deeply expressive miniatures that have remained neglected (a setting of Carl Sandburg's Fog is one of the American masterpieces in the genre). Harris also made substantial contributions to the solo cantata, his finest works in the category comprising a setting for mezzo-soprano and piano trio of Vachel Lindsay's Abraham Lincoln Walks at Midnight, a large work for baritone and orchestra on Whitman's Give Me the Splendid Silent Sun, and a monumental setting for high voice and chamber ensemble of St. Francis of Assisi's Canticle of the Sun. These works represent a peak in the employment of the composer's imaginative resources and, in their flexible integration of contrasts within smoothly unfolding large structures, in his craftsmanship.
Harris did not demonstrate a natural affinity for either the musical theater or the cinema, although they continued to intrigue him (especially during the 1960s and 70s, when he engaged in a number of abortive film and operatic projects, one of them a joint venture involving actress Hedy Lamarr). He evidently lacked adeptness in the musical depiction of specific actions and found it difficult to reconcile his autogenetic principles with the incisive character delineation and the sometimes sudden changes of scene fundamental to these genres. Nonetheless, there are a film score and several ballets, most of the latter composed for Hanya Holm (in addition, some of his pre-existing music was adapted for balletic presentation by Doris Humphrey and Eleanor King). All of his theater music is scored for various chamber ensembles. Perhaps the most successful of the ballets is From This Earth; this and the film score, One-Tenth of a Nation, which deals with the plight of blacks in the rural South, contain an abundance of distinctive ideas and skillfully devised textures. However, they are perhaps more successful as abstract concert pieces than as fulfillments of their original functions.
