In a letter to a young Willis Conover, H.P. Lovecraft explains a great deal about 'real' grimoires, volumes of magic from past times. At the end of the explanation Lovecraft says,
"But you will undoubtedly find all of this stuff very disappointing.
It is flat, childish, pompous, and unconvincing-merely a record of human
childishness and gullibility in past ages. Any good fiction-writer can
think up 'records of primal horror' which surpass in imaginative force
any occult production which has sprung from genuine credulousness."
I've seen Lovecraft say the same thing in other letters and it's why,
I suppose, he and those in his circle, made up their blasphemous books
from whole cloth. Cultes des Ghoules, Nameless Cults, Mysteries of the
Worm, and of course the fabled Necronomicon, are but a few of the
grimoires created by HPL and the gang. It seems that Lovecraft basically
thought that using 'real' magic books was a waste of time.
William Hope Hodgson, the creator of Carnacki the Ghost Finder,
apparently agreed. Carnacki is famous for his use of various lines of
the 'Saaamaaa Ritual' from the 'Sigsand Manuscript', an ancient text
created by Hodgson.
On the other hand, horror legend, Manly Wade Wellman, enjoyed using
real books in his stories, many of which he owned in his personal
library. In the stories of John the Balladeer and other Southern fantasy
and horror tales, Wellman liked to invoke 'The Long Lost Friend' which
is a book of white magic. I have a copy of this and did reference it in
the novel Congregations of the Dead.
When James A. Moore and I were writing the novel Blind Shadows, I
tried to pay homage to Wellman by having my occult detective, Carter
Decamp, use some of the same books Wellman had referenced, including
Spense's Encyclopedia of Occultism (Lovecraft DID own a copy of this
one), Cotton Mather's Wonders of the invisible World, and of course the
famous 1487 edition of Malleus Maleficarum, beloved by Witchfinders
I do think that use of such real books adds a bit of verisimilitude
for those in the know about such things. I know I got a kick out of it
in the John the Balladeer and John Thunstone stories.
However I have also added my own fictional grimoire 'The Silent
History' to the Cthulhu Mythos shelf. It contains lore so dangerous that
it must never, ever, be read aloud. Remember, things are listening out
there in the outer dark.