These final lines arrive as if in response to an unspoken statement by the steamroller, likely a broad generalization about butterflies. First, Moore’s speaker counters with doubts that the steamroller would even encounter a butterfly (“I can hardly conceive/of one’s attending upon you”). Second, the steamroller uses the theory of “the congruence of the complement”—the notion that all similar things are identical—rather than experience to understand butterflies, so Moore’s speaker knows that any attempts to help the steamroller reframe its views on butterflies would be in vain. Finally, the speaker includes a deflating phrase: “if it exists.” This suggests that “it”—the congruence in which the steamroller believes—does not exist. Again, the speaker uses complicated syntax and jargon to mock the steamroller with its own academic discourse. The sentence is a final blow at the steamroller’s generalizing principle.

The “congruence of the complement” is a geometric theorem which states that two angles which complement the same third angle are identical to each other. Such a theorem is equivalent to the steamroller’s understanding of the world, in which like objects are lumped together; differences are lost. Through such mathematical thinking, the world is made abstract.

In these lines, the speaker mocks the steamroller for its lack of subjectivity and feeling. The steamroller’s approach to “aesthetic matters” is “impersonal” and objective. In a satirical twist, the phrase “‘impersonal judgment in aesthetic/matters, a metaphysical impossibility’” is itself conveyed in an impersonal, academic tone. Moore’s use of quotation marks points to the satire of the phrase. The speaker uses the words, but disowns them.

This line offers an example of the speaker’s attentiveness to the world. The “particles” mentioned in the previous stanza become “sparkling chips of rock,” a vivid image conveyed through rich sounds. Note the consonance in particular—the repeated s, p, r, and k sounds. This is an example of language that brings us closer to the world through sound and detail, rather than cloaking it in abstract ideas.

The steamroller in this poem is often viewed as a stand-in for the literary critic, the reader who seeks to organize a text into a broad abstraction rather than experience a direct encounter with it. Moore’s speaker then stands in for the artist, the person who cherishes detail over abstraction, “particles” over “conformity.”

Moore’s central metaphor is that of the steamroller. Just as a steamroller flattens all the unique “particles” of concrete down into a smooth surface, the clumsy thinker or critic flattens the complexities of the world down into broad, abstract ideas.

Moore sets forth the poem’s central theme in the opening lines: that there are two approaches to the world. The first is an experiential approach to the world in all of its beautiful detail. The second is a theoretical approach in which the specific details of the world are lumped into broad generalizations, and thus lost. The addressee of the poem—the “you”—is someone who takes just such a theoretical approach. The speaker is interested in “illustration”—capturing the world as it is. The addressee is interested in the “application” of ideas to the world.

As in many of her poems, Moore uses syllabic verse, a poetic form with a fixed or constrained number of syllables per line. In each stanza, the four lines contain five, twelve, twelve, and fifteen syllables, respectively. The first two lines of each stanza rhyme, but the last two do not. Each stanza undergoes a progression from poetic to prosaic language as the rhymes slip away and the lines lengthen. The poetic tone represents the speaker’s voice, while the prosaic tone represents that of the steamroller, the academic, the critic.

The quotation marks around these lines suggest that the speaker is incorporating an external source in order to make her point. This quotation comes from an article written by Lawrence Gilman about the music of Leo Ornstein. This is not an allusion to a famous piece of criticism, but rather an obscure academic text used to bolster her point. This form of citation and obscurity adds to the academic tone of these lines. Ironically, the speaker uses the very means by which the steamroller communicates ideas in order to disprove its theoretical position.

In this line, the adjective “metaphysical” refers to reasoning, ideas, or theoretical principles. The word “impossibility” is simply the noun form of impossible. With this phrase, the speaker means that the objective judgement of aesthetics is impossible, even in theory. By using this jargon to communicate a simple concept, the speaker assumes a stilted, pompous, academic tone.

The science of sensory perception, “aesthetic” refers to a system of principles for the appreciation of the beautiful. This term underscores the tension in this poem between a theoretical approach to the world and an experiential approach to the world. A theoretical viewpoint believes that it can classify beauty and objectively understand it using a set of principles.

The phrase “impersonal judgement” means objective judgement, or objective thought. The adjective “impersonal” means not pertaining to or connected with any particular person. In other words, this is judgement unattached to a human bias.

The noun phrase “sparkling chips” is a metaphor for that which is unique, such as people, ideas, art, etc. The steamroller wants to crush all of these unique elements into one “parent block.” The “parent block” can be interpreted as a standard through which all unique elements are judged. In other words, the steamroller believes that it can create one standard that will apply to all things, rather than viewing each “sparkling chip” as a unique individual that cannot be reduced to a uniform pattern.

The image of the steamroller walking back and forth on the particles it has forced into conformity represents the limited knowledge offered by its worldview. Its theoretical or application-based approach to the world claims to create “understanding.” However, this understanding actually narrows the world into a single path that the steamroller is then forced to pace, which confines rather than expands.

On a literal level, the speaker is imagining a steamroller: a heavy, slow-moving vehicle that uses a giant roller to flatten the surfaces of roads during construction by pressing concrete or asphalt into a uniform surface, such as a sidewalk or a road. Once this uniform surface is created people can walk on it.

This insult can grammatically be read in two ways. A “half wit” is an insult that means a foolish or stupid person. The sentence could be interpreted as missing a verb and read “You are a lack half wit.” The sentence could also treat “lack” as a verb and read “you lack even a half wit.” This would further emphasize the speaker’s perception of the steamroller’s stupidity. It is so unintelligent that it does not have even half a brain.

These first lines set the poem up as a conversation between two people: the speaker and the “steamroller.” Moore’s poem is the response to an unstated question or claim that the steamroller has just made about its theoretical approach to the world. Notice that by setting up the poem in this way, the speaker is able to advance an argument without stating the other side and win the argument because the steamroller is not given the space to respond.