In the above-mentioned article, Sandburg argues that free verse is as old as rhythmic speech: "When primitive and prehistoric man first spoke with cadence or color," he writes, "making either musical meaning or melodic nonsense worth keeping and repeating for its definite and intrinsic values, then free verse was born, ages before the sonnet, the ballad, the verse forms wherein the writer or singer must be acutely conscious, even exquisitely aware, of how many syllables are to be arithmetically numbered per line." Whether or not one accepts this point, its presence in Sandburg's argument hints at the notion to which Sandburg responds: the idea that free verse is fundamentally and perhaps dangerously modern.

Critics have argued for lineages of free verse in English that reach back to the King James Bible (especially the Psalms and the Song of Solomon), William Blake's prophetic poems, and other sources. Writing free verse became an important and widespread movement in poetry, however, only in the latter half of the nineteenth century, when French writers experimented with vers libre and when the American Walt Whitman published many incarnations of his influential volume Leaves of Grass. In the twentieth century, free verse became the dominant mode of poets writing in English, to the extent that poets now can stand out by writing in regular forms.