What exactly does it mean to believe in fiction? What can this form of belief achieve or do for us that other forms cannot? This essay argues that for Oscar Wilde, the experience of losing oneself in a work of fiction offers a privileged opportunity to “try on” a belief one simultaneously knows to be not quite true or not quite one's own. In addition, it argues that in promoting this experience, Wilde is explicitly critiquing a model of belief popularized by Cardinal Newman in his 1870 An Essay in Aid of a Grammar of Assent. There, Newman claims that one knows when one's beliefs are true because “certitude [i.e., true belief] is accompanied … by a specific feeling, proper to it, and discriminating it from other states, intellectual and moral.” By contrast, In “The Portrait of Mr. W. H.” (1889) and elsewhere, Wilde attempts to make all beliefs seem open to doubt and debate—even beliefs not ordinarily understood as beliefs, such as sensations and emotions. Rather than advocating the “feeling of satisfaction and self-congratulation” that Newman identifies with certitude, Wilde seeks to make paradigmatic the ambiguity and, even more important, the vicariousness that he identifies with the experience of reading fiction.