Pre-eminent Lovecraft scholar S.T. Joshi divides “Lovecraftian” stories into three categories in his book “The Rise, Fall, and Rise of the Cthulhu Mythos”. The first category he calls the “Lovecraft Mythos”, stories that capture the purest form of cosmic horror that author H.P. Lovecraft sought to evoke when he wrote his horror stories in the early 1900’s. Lovecraft Mythos stories include many of the tropes and themes that Lovecraft was fond of using, such as fictional geographies, particularly in New England; ancient madness-inducing tomes; scholarly protagonists; and god-like monsters and extraterrestrials that care little to nothing about an insignificant humanity.
Very few writers achieved the “Lovecraft Mythos” status, according to Joshi. Even Lovecraft himself strayed from his own vision a few times with stories like “The Dunwich Horror”, which Joshi considers more of a dark pulpy adventure than an expression of cosmic horror. But Joshi, usually an acerbic critic, reserves his highest praise for the stories he considers part of the “Lovecraft Mythos”, including most of Lovecraft’s work, some writings from Lovecraft’s contemporaries, particularly Donald Wandrei, and more modern writers such as Ramsey Cambell, Caitlin R. Kiernan, Thomas Ligotti, and W.H. Pugmire.
Joshi’s second “Lovecraftian” category, and by far the largest, is the “Cthulhu Mythos” category. This includes stories that use many of Lovecraft’s story elements, particular his pantheon of monster-gods, but don’t quite achieve a true sense of cosmic horror. Joshi has mixed things to say about the writers of these types of stories, often praising them for their entertainment value, but criticizing their hollowness or their deviations from Lovecraft’s core themes. Most of Lovecraft’s contemporaries and friends wrote stories like this when they tried to emulate his work. More modern writers like Stephen King and Peter Straub also fall into this category. King and Straub, even though some of their stories include Lovecraftian elements (like King’s “Jerusalem’s Lot”, and Straub’s “Mr. X”), go for horror that is more visceral than cosmic.
The final category, and the one that Joshi piles scorn on, is the “Derleth Mythos”. The writer August Derleth corresponded with Lovecraft near the end of Lovecraft’s life, and was such a fan of Lovecraft’s work that he became Lovecraft’s self-appointed defender and promoter after Lovecraft died. He “finished” many stories that Lovecraft either started and didn’t finish, or merely wrote down the ideas for. But as Derleth continued to write more of these stories “with H.P. Lovecraft”, he began to change the themes to better suit his world view. Cosmic horror became more mundane, Earthly horror as Derleth added “good” gods to the pantheon to fight the “evil” ones. Derleth effectively pulp-ified Lovecraft and at the same time tried to convince people that it was all part of Lovecraft’s original vision. This led to the “fall” of the Cthulhu Mythos in the title of the book, around the mid 1900s, when most people’s exposure to Lovecraft was mainly through Derleth’s stories.
Joshi is a piercing critic and the most knowledgeable Lovecraft scholar working today. His fiction writing is not quite as good as his commentary (at a few points he even criticizes his own work), and as such some of the story summaries in the book are a bit bland. But his factual approach is still very enlightening. Anyone interested in an academic look at Lovecraft’s immense influence on literature should pick up “The Rise, Fall, and Rise of the Cthulhu Mythos”.