Though Charles Williams was already an established novelist before his friendship with Lewis blossomed, Lewis played a crucial role in helping to secure an honorary degree and teaching opportunities for Williams when he relocated to Oxford during the war. Their mutual appreciation is well attested to, and it is no exaggeration to say that Lewis would be a very different, and I would say, a lesser writer, where it not for his appropriation of significant elements of Williams’s spiritual vision. One of the issues for which Lewis took up Williams’s cause was the practice of substitution. This practice, elaborated in Williams’s theological and fictional works, as well as in his correspondence, speaks to the “arch-natural” character of a universe in which individuals can consciously and intentionally “bear one another’s burdens” of fear, anxiety, and possibly even physical sickness or pain. At various points, Lewis corroborated the legitimacy of this practice in Williams’s personal life, articulated and developed the practice in a literary context, and apparently came to question and refocus it in the later years of his life. Lewis’s settled legacy and credibility as a spiritual, theological, and literary authority make his appropriation and critique of substitution important for the ongoing evaluation of Williams’s own legacy and credibility.