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.
"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.