On the Operation of Demons

Psellus here delivers one of the more in depth works on demonology which has ever been made. Categorizing demons in the form of a Socratic dialogue between Timothy and Thracian, Psellus remarks upon the form, goals, and nature of the demonic realm in all its subsets. We see here, for the more secular reader, as well, a description of possession as a de facto mental state, and a description of speaking in tongues under such power as well. Moreover, the use of mind altering substances as a way of communication with such entities is not explicit here but indeed is implied.