Some characters have their knowledge of the universe modified, corrected, reversed, expanded and destroyed in different ways: some learn from first hand experience, whereas others learn from Forbidden Works: books, tomes and chronicles written through the ages.
Forbidden Works are often, but not ways, antique printed books. Because of their forbidden knowledge, they are printed in very limited numbers, many of which have been lost through the ages or destroyed. Different editions, along with different translations may introduce or subtract important information.
Forbidden Works can also take other literary forms, such as scrolls or tablets, or any other literary form that was commonly used in the culture of the publisher.
NOTE: It is even possible that a Forbidden Work loses its intrinsic value as a Forbidden Work because of changes. simply reprinting the visible letters of a previous edition may not convey all the information needed to gain any benefits or knowledge.
Forbidden Works hold three roles in the Lovecraft Universe:
Forbidden Knowledge
They not only inform but convince readers that conventional knowledge of the universe is either wrong or severely limited. Supposedly universal laws of time, space and matter are not consistent. What scientists know of the universe is true – except when its not. This is forbidden knowledge in the sense that not everything conveyed is necessarily true, but that some of it is.
Deep History
Most forbidden books were written by men who lived in ancient cultures. With human authorship, there is always an intention in writing the forbidden work. A forbidden work might be a book created as a holy scripture for an ancient cult. Another might be a chronicle of the travels of a scholar into an unknown land. Another might detail the drug addled dreams of a mad poet.
Hidden Power
Forbidden books also reveal different kinds of Formula. Some cultists, and believers in more conventional occult phenomenon may refer to these as spells or magical rituals. Calling them magic, much like calling them prayers, implies a framework of universal knowledge that can be as limited as any other that gets debunked in other Forbidden Works.
Forbidden Works and the Truth
Cultists and other extreme believers who have been consumed by their madness are less likely to gain as much as one might think from Forbidden Works. Clear headed, intelligent people are more likely to be able to pick out both the truth and the hidden power in Forbidden Works. The unfortunate side effect of gaining forbidden knowledge is the shock that drives one mad.