Although “Mirror” uses balanced stanzas and tight, seamless lines, its lack of rigid form and meter places it firmly in the free verse movement that was most popular during the mid-20th century. The complete lack of ornamentation—which fits the subject matter of the poem and the mirror’s insistence on its unfiltered view of the world—seems to flout antiquated poetic convention.

Plath’s poetry is part of the Confessional literary movement, a tradition that includes poets such as sometime-friend Anne Sexton, as well as Robert Lowell, who had an enormous influence on Plath’s work. “Mirror” is an example of this type of directly confessional poetry; rather than telling a narrative story, as many poets from the previous generation did, Confessional poetry speaks directly to the reader (or, as in some of Plath’s poems, to another character off the page) in first-person narration. This made Confessional poetry feel more intimate and universal, because these poets often explored themes that would resonate with many.

However, Confessional poetry’s critics use this intimate approach toward poetry as a problem with the movement. To critics, some Confession poetry delves too deeply into the poet’s private world, resulting in poetry that shares too much—even to the point of breaking social mores by inviting readers into previously explicitly private spheres (like abortion and sexual encounters).