Each of the five stanzas in “Ode on a Grecian Urn” uses a rhyme scheme that resembles a hybridized version of the English and Italian sonnet forms. That is, each stanza opens with the kind of quatrain most closely associated with the English sonnet (ABAB) and closes with a variation on the traditional sestet of the Italian sonnet (CDECDE). Significantly, however, Keats introduces variation into each sestet. Thus, despite each stanza beginning the same way (ABABCDE), each one ends with a slight variation on the final three rhymes. Stanzas 1 and 5 both end with DCE, stanza 2 ends with CED, and stanzas 3 and 4 end with CDE. Given that these rhymes are spread out on the page, they aren’t directly audible for the reader. That is, the shifting rhyme scheme becomes clear not in the reading, but rather through a detailed structural analysis of the poem as a whole. Only through such analysis can we begin to “hear” the variations. In this way, the poem’s variable rhyme scheme creates something like the unheard melodies the speaker references in stanza 2—those mysterious “spirit ditties of no tone” (line 14).

Keats also playfully echoes this distinction between “heard” and “unheard” melodies in his mixed use of exact and slant rhyme. Most of the rhymes in the poem are exact. In the opening stanza, for instance, three of the five total rhyme pairs form precise matches: “time”/”rhyme” (lines 2 and 4), “shape”/”escape” (5 and 9), and “both”/”loth” (6 and 8). However, Keats also features two slant rhymes that subtly tease the ear. The most obviously imprecise rhyme is that between “Arcady” and “ecstasy” (lines 7 and 10), which have different consonants in the final syllable. The more interesting example appears in the pairing of “quietness” and “express” (lines 1 and 3). Although both words end with the same “-ess” sound, there is a barely audible difference that comes from a subtle difference in these words’ stress patterns. The word “express” contains a straightforward distinction between an unstressed and a stressed syllable: “ex-press.” By contrast, “quietness” has two stressed syllables, but these stresses aren’t exactly equal—that is, the main stress falls on the first syllable, and a softer, secondary stress falls on the final syllable: “qui-et-ness.” The slant rhyme therefore comes from the nearly inaudible distinction between the full stress of “-press” and the softer stress of “-ness.”