In that sense, the skylark is almost an exact twin of the bird in Keats’s “Ode to a Nightingale”; both represent pure expression through their songs, and like the skylark, the nightingale “wast not born for death.” But while the nightingale is a bird of darkness, invisible in the shadowy forest glades, the skylark is a bird of daylight, invisible in the deep bright blue of the sky. The nightingale inspires Keats to feel “a drowsy numbness” of happiness that is also like pain, and that makes him think of death; the skylark inspires Shelley to feel a frantic, rapturous joy that has no part of pain. To Keats, human joy and sadness are inextricably linked, as he explains at length in the final stanza of the “Ode on Melancholy.” But the skylark sings free of all human error and complexity, and while listening to his song, the poet feels free of those things, too.
Structurally and linguistically, this poem is almost unique among Shelley’s works; its strange form of stanza, with four compact lines and one very long line, and its lilting, songlike diction (“profuse strains of unpremeditated art”) work to create the effect of spontaneous poetic expression flowing musically and naturally from the poet’s mind. Structurally, each stanza tends to make a single, quick point about the skylark, or to look at it in a sudden, brief new light; still, the poem does flow, and gradually advances the mini-narrative of the speaker watching the skylark flying higher and higher into the sky, and envying its untrammeled inspiration—which, if he were to capture it in words, would cause the world to listen.