"metaphysical impossibility..."See in text(Text of the Poem)
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.
"impersonal judgment..."See in text(Text of the Poem)
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.
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.
"You lack half wit..."See in text(Text of the Poem)
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.
