Wordsworth published 523 sonnets, including one called “Scorn Not the Sonnet” (1827), in which he compares the sonnet to a key that helped Shakespeare unlock his heart and a lute whose melody “gave ease to Petrarch’s wound.”

“Composed upon Westminster Bridge, September 3, 1802” is a Petrarchan sonnet. Like a Shakespearean sonnet, Petrarchan sonnets contain 14 lines. Unlike the Shakespearean sonnet, the Petrarchan Sonnet has a more irregular and complex rhyme scheme, an eight-line stanza (octave) rhyming ABBAABBA, and a six-line stanza (sestet) rhyming CDCDCD or CDECDE. This rhyme scheme creates a sense of musicality and order. It indicates that there is a flow and arrangement to the universe, perhaps designed by a benevolent deity, in keeping with Wordsworth’s religious convictions. Much like how the banks of a river contain an overwhelming flood of water, this structure can contain the abundant flow of feelings that Wordsworth often tries to convey in his poetry.

For Wordsworth, the sonnet, which means “little song,” is a structure that helps unlock feelings and create a sense of harmony and beauty. It is appropriate he used this form to delineate, or outline, the feelings he experienced while standing on Westminster Bridge, as the poem is about experiencing a moment of harmonious tranquility.