Freud wrote on the concept of paranoia, the condition that, among other things, leads one to imagine conspiracies. See how the following summary of Freud and paranoia resonates with Eco's novel:
"In Freud's description, paranoia is a fixation on oneself and a progressive exclusion of the external world brought the mechanism of projection. Paranoia is a logically reasoned delusion usually involving persecution or grandeur. The paranoiac believes that there is a pattern to random events and that everything is somehow connected to him or her. The rational quality of this delusion is very important; every element and detail makes sense within a closed system that is based on a delusionary premise. For example, the proposition "I hate him" becomes transformed by projection into, "He hates (persecutes) me, which will justify me in hating him," and then, "I do not love him- I hate him, because he PERSECUTES me."
Svetlana Boym, '"Conspiracy Theories and Literary Ethics: Umberto Eco, Danilo Kis and The Protocols of Zion", Comparative Literature, Spring 1999, at 99.