This paper considers the problem of detecting deceptive agents in a conversational context. We argue that distinguishing between types of deception is required to generate successful action. This consideration motivates a novel taxonomy of deceptive and ignorant mental states, emphasizing the importance of an ulterior motive when classifying deceptive agents. After illustrating this taxonomy with a sequence of examples, we introduce a Framework for Identifying Deceptive Entities (FIDE) and demonstrate that FIDE has the representational power to distinguish between the members of our taxonomy. We conclude with some conjectures about how FIDE could be used for inference.