Basic Information
The Tome of Eldritch Lore is a horror trope. The tome is a book which contains forbidden and dark knowledge which is likely to drive the reader insane and cause all sorts of other detrimental side effects as well - even if no one is actively reading it in some cases.
The ur-example is probably H.P. Lovecraft's Necronomicon - although the idea of the grimoire is far older. Lovecraft's creation was specifically of the "repository of things Man was not meant to know", but other examples could well include books of spells and lists of demon names. Indeed, even without Lovecraft's context, the direct translation of Necronomicon as "book of the names of the dead" suggests that it might be a useful tool of necromancy.
More fantastical examples can turn out to be the laboratory notebooks of one or more wizards, know for their groundbreaking research. Even if these wizards were positively reputed, such knowledge - especially where "experimental write-ups" are incomplete or fail to mention (or explain) the "standard safety precautions", this can still be dangerous. The edgier the wizard, the dodgier the research. Also, expect such things to be far from clear - in environments without IP law and/or where people are worried about their work being stolen and/or misused - expect a great deal of allusion, metaphor and outright encoding.
"Whiter" versions of this book may be, effectively, magical textbooks - explanatory texts setting forth points of thaumatology for the benefit of students. The context in which such a thing would be written bears careful consideration1.
There is also the small matter of publishing to consider. In context, these are not the sort of books that one simply orders from an academic bookseller - or, indeed, publishes, given that the proof-reading and typesetting process is often hard on the reader and, as noted above, the authors are rarely the sort of people who want to be published anyway. Bona Fide copies are likely hand transcribed, possibly illicitly and likely by someone who did not fully understand what he was copying (at the time or ever)2. They must then suffer from edits, hand inserted errata and the commentary and marginalia of a variety of authors. Bits the copyist considered irrelevant may be omitted and things a later possessor thought relevant pasted in … including prolonged rants, digressions and speculation, not all of it of the same quality as the original. Things - especially diagrams and tables - may be cut out and pinned to a wall somewhere, gatefold illustrations lost and other deletions made - and contrary, other things may be deliberately or accidentally pasted over the text (from plants being pressed for use in a hortus siccus to insects, pieces of food or insane doodles). Some of these marginalia may be improvements (see, for example the lite culture version in Harry Potter and the Half-Blood Prince where a school textbook is annotated by someone far more competent than the author). The book may also be have been inexpertly bound or re-bound, possibly with other texts (perhaps by way of a disguise) and possibly in the wrong order. Physical damage, by water, sunlight, fire and laboratory chemicals are all distinct possibilities, as are partial consumption by vermin and fungi.
The fantasy RPG market has tended to cheapen these things somewhat due to the high prevalence of the spellbook in many systems and settings - although even these can have works that can stand up alongside their fictional and legendary peers. The Book of Vile Darkness and similar works from the Dungeons and Dragons metaverse would be good examples of the type3.
Real world books belonging to this category include: Romanus-Buchlein, Picatrix, the Corpus Hermetica, Egyptian Secrets of Albertus Magnus, The Sixth and Seventh Books of Moses, The Lesser Key of Solomon, Petit Albert and Powwows, or "the long lost friend". The Ancient Egyptian Book of the Dead was an interesting variation on the theme, being essentially a selection of "cheat codes" provided to a deceased soul amongst its grave goods to allow it to better overcome the various trials awaiting on the way into the afterlife. Many more exist.
See Also
- Artifact Of Doom
- Book Of Shadows
- Codex Gigas
- Necronomicon
- Scanned Multi-Alphabet Arabic Manuscript Online
Sources
Game and Story Use
- Mandatory for Cosmic Horror campaigns.
- In settings where invocation - and outright summon magic - are popular, the names of spirits and demons, used as part of summoning and binding rituals, are prone to be a significant currency amongst users. Obviously, such knowledge is unlikely to be published, but each worker might keep their own registry - probably including any other information on the entities in question, records of successful (and unsuccessful) summonings and, if applicable, notes on preferred payments and bargains. Such a registry that comprised a lifetime's records from someone known to have controlled a great many spirits might be a significant prize.
- Can also apply to ward magic: in The Rainbow Abyss, wizards trade the names of hostile spirits so that they can more easily protect themselves.
- Cost/benefit for use of these things should depend upon setting - horrific secrets about the true nature of reality may be more harmful (and less use) than a demon summoner's journal (although in a wainscot fantasy setting, such a thing might be unnerving even if the reader didn't actually believe in the supernatural.
- Important to consider who wrote the book and why - the darker the magic involved, the more likely it is that the book was written with ill intent; it would be entirely normal for the sort of person that practices left hand path magic to leave behind a record that is deliberately misleading or dangerous so as to cut down on "the competition" (even to the extent of tampering with other people's previously safe work. Alternatively, a given book of magic might turn out to be the thaumatological equivalent of The Anarchist's Cookbook - a collection of deliberately dangerous techniques propagated by what might loosely be considered law enforcement to eliminate (or at least scare off) would be troublemakers.
- In the Dresdenverse the wardens of the White Council (essentially the magic police) are known to distribute ill intentioned magical rituals as widely as they can - in universe such rituals call on a specific, fixed source of power so the more people who try to use it, the less chance there is of any one of them getting enough energy from it to achieve anything.
- Realistically, there are likely to be a great many books on the occult in any setting where it is presumed to exist - there are enough floating about the real world in which such things remain at best unproven - so any world where magic is a genuine force will likely have a lot more. Some will be actual grimoires, containing direct magical knowledge, but others are likely to address satellite subjects. This should mean that the wizard's library need not contain solely spellbooks, but also treatises on astrology, the nature of other planes of being, the magical properties - real, conjectured or otherwise - of plants and animals, books of arcane philosophy … all sorts of things that a wizard might need to know in order to practise or research his art. You can then add books on pretty much anything else given that, unless obsessively focused on his art, a wizard is likely to have the intelligent man's typical hunger for knowledge and read widely and voraciously in any field open to him.