The particular to which Stevens refers in "The Course of a Particular" is at once himself and the phenomenon that absorbs his attention: the "cry" of the leaves on a winter day. The course of the poem is a meditation in which Stevens inverts the visionary process through which he comes to a realization of essential unity. As he listens to the sound of the leaves in the wind, he recedes into a state of alienation from the world around him … Stevens only gradually clarifies for himself the significance of the cry he hears/ The declaration in the ninth line constitutes a climactic recognition. The force that "gives life as it is" is a force of particularity, that is, of "difference." In the first stanza, the cry of the leaves seems to associate itself with "the nothingness of winter" and also, paradoxically, to contribute to the diminution of spiritual negativity. The "icy shades and sharpen snow" recall the landscape of "The Snow Man," a recollection that may help to account for the ambiguous mingling of nothingness and the incipient animism in the cry of the leaves. In the second stanza, perhaps because the nothingness of winter has become a little less, Stevens suggests that the cry is potentially meaningful, but only to "someone else," and his sense of alienation expands to include the social world. The declaration "being part is an exertion that declines" includes both the world of particular objects and the people who concern themselves with those objects.
Once he has clearly recognized "the life of that which gives life as it is," Stevens drives toward a complete inversion of the pure principle. He drains out the incipient animism in the leaves" cry, which, though it is a meaningless sound, echoes with the ironic pathos of spiritual absence. …In Stevens" visionary poetry, man is an object of "divine attention" because he is the special locus of sentience through which the essential poem achieves its "difficult apperception" [from stanza I, "A Primitive Like an Orb"]. The divine attention can be realized only through the forms of thought that are also the forms of phenomenal reality. These forms are the "fantasia" of the supreme fiction. The pure principle of sentient relation can articulate itself only in metaphorical displacements, "the intricate evasion of as" [from stanza XXVIII, "An Ordinary Evening in New Haven"] . The principle of difference manifests itself … in a reduction to the literal, "life as it is." The forms of thought reduce themselves to "the final finding of the ear," and the forms of phenomenal reality reduce themselves to "the thing / Itself." In the absence of fantasia, these two aspects of particularity, the self and the world, are equivalent in their meaninglessness. Stevens repudiates essential unity, but he does not then revert to a celebration of the parts of the world. The failure of transcendental affect leaves him at the nadir of the cycle from Romanticism to indifferentism.
From Joseph Carroll, Wallace Stevens’ Supreme Fiction: A New Romanticism (Baton Rouge: Louisiana State University Press, 1987), 305-306.