Cather recalls her attempts to apply mathematical formulae to an analysis of the text of the play as per her training by L. A. Sherman at the University of Nebraska.
In "Flavia and Her Artists," when the guests leave Flavia's house, Jemima Broadwood refers to them as "the great doom's image" (II:3, 78). Broadwood also compares Arthur Hamilton's fate to that of Macbeth when she says: "Why he has sacrificed himself to spare the very vanity that devours him, put rancours in the vessels of his peace, and his eternal jewel given to the common enemy of man, to make them kings, the seed of Banquo kings!" (Macbeth III.1. 65-69
In The Professor's House, Godfrey St. Peter's "desire to do [his "great work"] and the difficulties attending such a project strove together in his mind like Macbeth's two spent swimmers." The reference is to Macbeth I.ii. 8-9: "As two spent swimmers, that do cling together/And choke their art."
In Lucy Gayheart, Clement Sebastian "remembered Macbeth's Oh, full of scorpions is my mind, dear wife!" when he hears of Larry MacGowan's death (Macbeth III.2.36).
In writing to her Aunt Franc upon learning of G.P. Cather's death, Cather "remembered the last act of Macbeth and the line of Old Siward, who upon learning that his son had died nobly in battle, exclaims, 'Why then, God's soldier be he!'" (Macbeth V.8.55).