The Back-Ache appears in Wallace Stevens' poem "Saint John and the Back-Ache" (1950) as a formidable presence of pain as an antithesis to the presence of mind, or in the case of Saint John, perhaps a perceived presence of God. Ronald Sukenick, in Wallace Stevens: Musing the Obscure (1967), states that "Stevens' poetry deals in a series of antithetic terms, . . . and [t]he repeated recombination of the terms . . . produces a continual restatement of the shifting relation between them . . ..  Within the poem, a dialogue develops between the Back-Ache and Saint John, and the Back-Ache appears to represent reality while Saint John's mind represents the imagination. The reader can conclude by the end of the poem that reality always manages to make its presence known, regardless of the power of the mind. More importantly, the pain itself may move the mind beyond the imagination into a genuine presence of God. See John Locke.
Sukenick, Ronald. Wallace Stevens: Musing the Obscure. New York: NYUP, 1967. Print.