In the Oxford Book of Modern Verse 1892–1935, 378 numbered poems idiosyncratically ‘Chosen by’ William Butler Yeats and published in 1936, Yeats not only affirmed the modernism of ‘aestheticist’ Walter Pater by including him in this volume but also declared him a poet by lineating a single sentence from Pater's essay on the Mona Lisa. That generic border between prose and poetry had, of course, been breached on the continent at least half a century earlier by Baudelaire, perhaps the inventor of the modern as an ‘ism’, who had shown the way in his posthumously published Petits Poemes en prose, the collection much more commonly known as Le Spleen de Paris (1869). Baudelaire's heir, Arthur Rimbaud, followed with the visionary surrealities of Une Saison en enfer (1873, translated as A Season in Hell) and Iluminations (1874), where language breaks its tether to our mundane world. James Joyce, of course, offered a like decoupling in Finnegans Wake, where the rubric is bound to example: ‘Hear we here her first poseproem. […]’ (FW 528). For Joyce the ‘poseproem’ had the requisite musicality of poetry but its language took on a materiality as well, a linguistic opacity whereby words function more like things than referential transparencies or signposts to a stable, knowable world. Rimbaud and Joyce put the lie to any suggestion that the prose poem (or ‘poseproem’) was other than a discrete genre, merely something potentially akin to vignette. Theirs were decidedly unlineated poems. Yeats found in Pater the British equivalent of Baudelaire's final poetic project: ‘Who among us on his more ambitious days has not dreamed of the miracle of a poetic prose, musical but with neither meter nor rhyme, supple enough and rugged enough to lend itself to the lyrical movements of the soul, to the undulations of reverie, to the jolts and spasms of conscience?’ (Baudelaire 2000). Yeats heard that music in Pater, whose prose seemed metrical to the poet's ear, and he noted in his ‘Introduction’: ‘Only by printing it in vers libre can one show its revolutionary importance. Pater was accustomed to give each sentence a separate page of manuscript, isolating and analyzing its rhythm’ (Yeats 1936: viii).