As the title suggests, this poem is about the distinction between reality, and our interpretation of that reality, based on what we perceive with our senses. The “he” in the poem is just waking up; the sun is rising, and he hears a cry from outside. He gradually becomes aware of the world around him—the world beyond his sleeping one—by considering and reconsidering the sound of the bird’s cry, and the light of the sun. At first, he’s not able to clearly distinguish reality from the elements of his imagination, so he can’t tell whether the bird’s cry and the sunlight are real or are simply a lingering part of his dream. But he soon comes to discover (or rediscover) the immensity of the outside world and the line that separates it from the comfort of his own mind. This realization is “like / a new knowledge of reality” (lines 17-8).
Ultimately, however, Stevens believed that the only truth in reality comes from our perception of that reality. “Not Ideas About the Thing But the Thing Itself” is the last poem in The Collected Poems of Wallace Stevens. Stevens leaves us with, as Weston says, “the courage to accept the possibility that our every definition of reality is a regulative and saving fiction” (141). Stevens addresses the interaction between reality and the mind in many of his poems, but perhaps never with such eloquence and encompassment as in this poem.
Recordings also found here.