A simile is a compassion between two supposedly unlike things, making an explicit comparison via the words “like” and “as.”
By including multiple similes in “Ars Poetica,” Archibald MacLeish is possibly putting his theories about poetry into practice. In the poem, MacLeish expresses his belief that a poem needn’t be a hyper intellectual creation that’s nearly impossible to grasp. According to “Ars Poetica,” a poem should be “dumb,” “motionless,” and “equal.”
The use of similes might reinforce the “dumb” quality that MacLeish want for his poems. Similes tend to be thought as more simplistic and elementary than other poetic devices, including the aforementioned metaphor.
Furthermore, similes could help convey the “motionless” meaning of MacLeish’s poem because similes can be thought of as stills. Unlike metaphors, similes tend to be less active. A simile typically provides a motionless picture of two things not a sequence of events.
Finally, similes support the “equal” meaning because similes have a way of making these two unlike things seem like one another—as if they’re on equal footing. For example, MacLeish writes: “A poem should be wordless / As the flight of birds.” With this couplet, the simile brings the poem and the birds together. It turns them into equals.