“Summertime” is the opening aria in Gershwin’s opera “Porgy & Bess,” which portrays several black characters living in the slums of Charleston, South Carolina. The song itself is a lullaby for the singer’s baby, and the lyrics speak of prosperity and security: “The livin’ is easy / Fish are jumpin’, and the cotton is high / Your daddy’s rich, and your momma’s good lookin’ / So hush little baby, don’t you cry.” As several other people have pointed out, the song is highly ironic: the singer and baby are poor and black during the Jim Crow era, and thus, the lyrics offer false comfort. When I listened to it with that context, the song sounded like a lament: the tempo is slow, the key is minor, and the singer sings at a soft volume for most of the piece.
In addition to irony, the song’s musical characteristics also give it a dreamy and fantastic affect–both reflecting the laziness of a summer evening (where the opera opens) and the singer dreaming of a better life. For starters, the opening instrumental music (0:00-0:21) strongly reminded me of Debussy’s “Prelude à l’après-midi d’un faune”—the key and tempo are indeterminate and free, which gives a sense of mystery or fantasy (like a dream sequence in a movie). Then, once the singing begins, the strings play a very simple rising and falling melody that lasts for most of the song (e.g., 0:22-0:34). The meter of the melody gently rocks back and forth—which is fitting, since the song is a lullaby. Moreover, although Gershwin uses lots of dissonance in both the vocal and instrumental melodies, it isn’t a harsh dissonance, like the “cry of despair” in Mahler’s symphony. Rather, it’s more like the dissonance in Debussy’s piece, which sounds magical and mysterious: for instance, at “And the livin’ is easy” (0:33-0:39) and “And the cotton is high” (0:49-0:57), the singer and orchestra drop into a dissonant melody, which sounds more fantastic or dreamlike than tragic or unsettling. Another such example comes toward the end of the piece around 2:46-3:03, where the singer is joined by a chorus on “by” (in “with your daddy and your mammy standin’ by”): the melody soars, then falls slowly, changing to various chords along the way. Although some are dissonant, the overall affect of this section is, again, dreamlike and fantastic.
Thus, while the lyrics in “Summertime” are certainly ironic and tragic in one sense, Gershwin also portrays the sleepiness of a summer evening and the dreams of the singer by employing a steady, slow rhythm and “magical”-sounding dissonance.
(Sources: Porgy & Bess libretto, http://www.philipp-harnoncourt.com/Libretto%20PORGY%20AND%20BESS,%20engl.%20u.%20deutsch%20(P.H.).pdf)