The paper offers a three-premise argument that a person with first-hand experience of possession and exorcism, such as an exorcist, can have a justified belief in the existence of demons. (1) “Exorcism involves a process by which the exorcist comes to believe that testimony is offered by a demon.” Cited for (1) are the Gospels, the Roman Ritual, some modern cases of exorcism, and exorcism practices in non-Christian contexts. (2) “If defeaters are absent, the exorcist may treat as reliable the (...) process by which he comes to believe that testimony is offered by a demon.” For (2) a case is offered that we have a reliable ability to identify when testimony is being offered and when it is being offered by particular types of agents, what is termed testifier-identification. (3) “In many cases of exorcism, defeaters are absent.” An inductive case is given for (3) by responding to possible defeaters, including several suggested recently by David Kyle Johnson. Therefore, in many cases of exorcism the exorcist may treat as reliable the processes by which he comes to believe that testimony is offered by a demon, and so can have a justified belief in the existence of demons. (shrink)