This article makes the following case: according to Artemidorus of Daldis’ Oneirocriticon one main task of the dream interpreter is to identify, through knowledge of the dreamer, which components of a dream are internal in order to assess—as far as possible—the external components of a dream. I argue that very similar hermeneutic issues were being extensively theorised in Artemidorus’ period by Jewish and Christian writers who were concerned with the problem of prophetic interpolation: in particular, cases in the Bible in which prophecies do not come true. In making this comparison, I hope to clarify a number of features of Artemidorus’ hermeneutic, including the relationship between the origin and structure of dreams and the exegetical practice of the dream-interpreter
