“Ars Poetica” by Archibald MacLeish has twenty-four lines coupled into two line pairs that comprise twelve stanzas. These stanzas are separated into three different sections of four stanzas each. Many of the paired lines rhyme with perfect rhyme or slant rhyme, but others resist rhyming at all.
While the poem seems to start out in fixed form, with the first line being metrically measured in iambic pentameter, it quickly strays into free verse form, which defies the outdated poetic tradition of consistently using a single metrical pattern.
Below, all caps is used to denote stressed syllables in the first line, and lines separate the feet that group iambs:
a PO-|em SHOULD| be PAL|-pa-BLE |and MUTE
By the second line, the metrical rhythm of iambic pentameter is already broken, and it does not reappear until line six:
of CASE-|ment LEDG-|es WHERE| the MOSS |has GROWN
These iambic pentameter lines create a steady heartbeat rhythm, which abruptly halts with the shortened, unmetered lines that follow them. It is as if the uneven form is saying that while modern poetry came from a tradition of fixed metrical forms, that tradition is dead.
Elsewhere, MacLeish plays with other metrical patterns, such as the trochees found in line 12. Line 11 has an unsteady metrical pattern that begins with a trochee (stressed/unstressed), and then progresses into an anapest (unstressed/unstressed/stressed), and then includes an iamb (unstressed/stressed), and finally ends on an extra syllable, a single feminine ending (or an unstressed syllable). But line twelve switches back into a traditional metrical pattern where it suddenly shifts into trochaic tetrameter, with an extra stressed syllable at the end (or a masculine ending).
LEAV-ing, |as the MOON |re-LEASE-|es
TWIG by |TWIG the |NIGHT en-|TANG-led |TREES,
This intermittent appearance of metrical forms reminds the reader of traditional fixed form aesthetic theories of poetry, which largely grew out of ancient Greek poetic tradition. For instance, in his Manifesto, “Ars Poetica,” or “The Art of Poetry,” Horace theorizes that Homer’s use of dactylic hexameter for epics set the standard for poetry of epic content. This is just one example of where Horace argued that there are fixed forms more suitable to one subject matter than another. MacLeish’s choice to use free verse in this poem, with intermittent metrical forms, seems to put the poem in opposition to Horace’s outdated aesthetic ideas about poetry. Where lines briefly touch and break away from a fixed metrical pattern, MacLeish seems to argue that a poem’s form should be free to whimsically change from moment to moment.