Conversion apparently involves the most powerful of the certainty-experiences.
In Augustine's case, however, the incubation period is quite evident. Whatever the precise mechanism of conversion may be, it is plainly an experience beyond rational assent. Most surely, a path of rational assent may precede or follow a conversion, but it is not the conversion itself. The actual experience is irreducibly affective and immediately present to the self. This helps to account for the passive character of mystical experiences and is supported by the knot of emotional-physical responses contained in almost every tale of conversion cited by James.