In 1928, MacLeish produced what many consider to be the defining manifesto for modernist poetry, “Ars Poetica,” with the famous concluding line insisting that
“A poem should not mean / But be.”
One of the conventions of modernism was, perhaps paradoxically, experimentation in meaning and form. Macleish wrote "Ars Poetica" at the beginning of his career, and published it in his collection Streets in the Moon, near the height of modernism. As MacLeish aged, his verse style changed. “Ars Poetica” and other poems composed during that time in Paris stand in stark contrast to the more traditional and perhaps more accessible poetry of his later years.
Just four years after publishing “Ars Poetica” and just shy of a decade after making that leap of faith to head for Paris and pursue his passion, MacLeish was awarded the first of his three Pulitzer Prizes. In the interim, his manifesto-like poem had been part of a poetry movement that was—almost irrefutably—distinct in purpose from almost all poetry ever written. Of course, MacLeish’s later poetry, which seemed to try to create some meaning not subservient to being, became examples of his rebellion against this early manifesto.