Listening, in Shelley's hands, is a dangerous activity. The speaker of this poem hears Constantia sing and does not simply admire her. He is overwhelmed, carried off and nearly erased. The opening question sets the stakes: to be "lost" and to "sink and die" in this way "perchance were death indeed." The rest of the poem tests that idea. The speaker's self does dissolve, but into something closer to bliss than to ending, and the poem ends with the soul suspended in what it calls "voluptuous flight."
The first stanza is the most fragile. The singing seems to have paused, since her voice is "laid to sleep," yet it survives in her breath and hair "like odour" and in her touch, which makes fire "leap." The speaker writes while his cheeks are "wet," so the music has become something remembered, or something that has not stopped hurting. The final line, "the torn heart can bleed, but not forget," hints at pain, but the poem never says what caused it. That silence suggests the sorrow is bound up in the singing itself. The line lengths also behave oddly. Short lines such as "are laid to sleep" sit beside long, sprawling ones, and the stanza ends on a stretched line that sighs out like a held breath.
From there the poem takes off. The second stanza turns the song into a flight. Her "fast ascending numbers" is a neat double meaning, because "numbers" can mean both musical phrases and lines of verse. The sky is "rent and cloven," violent words that rhyme with the gentle "woven," the word for the wings that sprout on the speaker's shoulders. Tearing and weaving happen together, as if the music breaks the world open and equips him to leave it. He passes "the mighty moons that wane" and the "world's shadowy walls," and the last line is long enough that it seems to run past the usual edge of the stanza too.
The third stanza changes the pronoun. The speaker has been saying "thy" and "thou," but now it is "Her voice," as though the voice has detached from the woman and become a creature of its own, "hovering" with "soft and lulling wings." The senses cross over, so that "the blood is listening," and the body takes over from the mind: the brain is wild, breath quick, and the heart "quivering like a flame." Then comes the stanza's central image of "morning dew, that in the sunbeam dies." It returns to the opening fear of dying, but death now looks like evaporating into light. The rhymes "eyes," "dies" and "ecstasies" make the same point by packing the stanza's most intense words into a tight run.
The last stanza gives up everything: "I have no life, Constantia, now, but thee." Her song becomes the "world-surrounding air," and it has two moods. First it is a "tempest swift and strong," yet the speaker feels "secure o'er rocks and waves," a nice paradox in which the wildest force is also the safest. Then it becomes the "breath of summer night" near "western isles," and the poem slows down. "Lingering, suspends my soul" is full of long, dragging sounds, and the closing rhymes "night," "bright" and "flight" leave the speaker hanging in mid-air. Every stanza ends with a run of three rhymes, and each one works like a wave breaking. The last three stanzas also share one rhyme pattern, so the song, once it begins, is more orderly than the broken, uneven opening.
Shelley is a Romantic poet, and the poem shows a Romantic faith in art as a force that can lift a person beyond ordinary life. His speaker is also carried by winds and clouds in "Ode to the West Wind," though there he pleads to be lifted and here the voice simply takes him. The poem's strangeness lies in how little of Constantia herself remains. She turns into air, storm and summer night, and the speaker shrinks to a pulse and a pair of wet eyes. That is both its thrill and its risk, because the poem's most intense praise of a person works by making her into weather.