Constructionally, the sonnet consists of only three declarative sentences, equivalent opposites, with the types shifting from compound-complex to complex to simple; decreasing in length from eight lines to four lines to two lines. He thus unifies the poem by lessening the length of the sentences but having them gain in importance, climaxing his thought with a terse simple sentence ending in an appositive expression.
Within the sentence construct, observe that line two ends with the word why which introduces the constituent sentence "Why the little buried mole continues blind," and line four begins with the word why which introduces the constituent sentence "Why flesh that mirrors Him must some day die." Note that positionally as well as characteristically they are equivalent opposites. Syntactically, however, they are equivalent comparables, both serving as direct objects of the verb phrase could tell, the subject He being understood. Moreover line twelve, "What awful brain compels His awful hand " not only couples with line four structurally, but positionally as well. It also has syntactical equivalence to both aforementioned constituent sentences, since it, as they, serves as the direct object of the transitive verb form, in this case to understand.
A further look at the verb constructs reveals that the clauses "did He stoop" in line two and "do I marvel" in line thirteen both maintain equivalent positions following the introductory joining words and and yet, and that both verb phrases are split by their pronoun opposite subjects He and I. Similarly, equivalent positions are held by the infinitives "to struggle" in line eight and "to make" in line fourteen, although their complements, a prepositional phrase following the former and a direct object and objective complement following the latter are equivalent opposites; while the infinitive "to understand" is complemented by the noun clause "What awful brain compels His awful hand," still another opposite.
Besides the coupling of larger constructions, Cullen couples words in a series in line one, good, well-meaning, kind, all modifying God, and in compound, inscrutible, Immune, in line nine, both modifying the noun ways. Moreover, he has coupled the noun phrases "awful brain" and "awful mind" in line twelve in opposite positions to the verb compels, one before and one after, and in opposite relations to the verb, the former as subject, the latter as object. So much for positional and syntactical coupling!
No less pronounced is Cullen's use of coupling of the Type II equivalences, concerned with phonics and semantics. Phonically he has elaborately employed alliteration throughout the poem in such couples as mole, mirrors, must, and mind; buried, blind, baited, bid, by, brain, and brute; did, day, and die; God, good; fickle, fruit; tortured, Tantalus; Sisyphus, stair, stoop, struggle, and strewn.
Moreover, in line one, he couples five of the eight words in the line phonetically—doubt, not, that; God and good; the first three of these words ending with the voiceless, alveolar stop /t/; the last two beginning with the voiced velar stop /g/ and ending with the voiced alveolar stop /d/. Furthermore, Cullen makes such frequent use of the alveolar stop /d/ in words like doubt, did, day, die declare to begin the word and in the words kind, buried, blind, tortured, baited, mind, understand, and hand to end the word that throughout the poem one senses the "doom" of his indecision which follows.
Finally, in Type II equivalences Cullen employs the paradigm of coupling involving semantics. There is first his coupling of synonymous adjectives, good, well-meaning, kind, in his description of God, all pointing out His excellent qualities in line one; and of His ways, inscrutable, immune, both depicting a sense of impenetrability in line nine, utilizing comparables in both cases. He then moves from the area of word coupling to that of incident coupling; first, coupling opposite extremes, the lowly mole and the regal kings; then comparables, Sisyphus and Tantalus, equivalent in social status, in the enormity of their crimes, in the severity of their punishment, and in their placement in literature, both mythical characters. In addition, there is the contrast in religious beliefs—the Christian God on the one hand, the mythical gods on the other.
It thus becomes evident that Cullen's use of coupling was not accidental, nor was it merely a succession of syntagms, but rather a combination with a system of paradigms which W. Nelson Francis describes as "A system of morphemic variations which corresponds to a parallel system of variations in environment (and hence of structural meaning)."
Cullen skillfully employed Types I and II, coupling positional and natural equivalences, alternating comparables and opposites, in unifying his fate-filled sonnet, the better to signify his complete frustration portrayed in the final line, " To make a poet black and bid him sing,." In so doing, he has indeed fulfilled the principle of equivalence from axis of selection into the axis of combination."