Now all my tales are based on the fundamental premise that common human laws and interests and emotions have no validity or significance in the vast cosmos-at-large. To me there is nothing but puerility in a tale in which the human form—and the local human passions and conditions and standards—are depicted as native to other worlds or other universes. To achieve the essence of real externality, whether of time or space or dimension, one must forget that such things as organic life, good and evil, love and hate, and all such local attributes of a negligible and temporary race called mankind, have any existence at all. Only the human scenes and characters must have human qualities. These must be handled with unsparing realism, (not catch-penny romanticism) but when we cross the line to the boundless and hideous unknown—the shadow-haunted Outside—we must remember to leave our humanity and terrestrialism at the threshold.
— H. P. Lovecraft, in note to the editor of Weird Tales, on resubmission of "The Call of Cthulhu"
The central theme of Lovecraft's corpus is cosmicism. Cosmicism is a literary philosophy that argues that humanity is an insignificant force in the universe. Despite appearing pessimistic, Lovecraft thought of himself being as being a cosmic indifferentist, which is expressed in his fiction. In it, human beings are often subject to powerful beings and other cosmic forces, but these forces are not so much malevolent as they are indifferent toward humanity. He believed in a meaningless, mechanical, and uncaring universe that human beings could never fully understand. There is no allowance for beliefs that could not be supported scientifically. Lovecraft first articulated this philosophy in 1921, but he did not fully incorporate it into his fiction until five years later. "Dagon", "Beyond the Wall of Sleep", and "The Temple" contain early depictions of this concept, but the majority of his early tales do not analyze the concept. "Nyarlathotep" interprets the collapse of human civilization as being a corollary to the collapse of the universe. "The Call of Cthulhu" represents an intensification of this theme. In it, Lovecraft introduces the idea of alien influences on humanity, which would come to dominate all subsequent works. In these works, Lovecraft expresses cosmicism through the usage of confirmation rather than revelation. Lovecraftian protagonists do not learn that they are insignificant. Instead, they already know it and have it confirmed to them through an event.
Decline of civilization
For much of his life, Lovecraft was fixated on the concepts of decline and decadence. More specifically, he thought that the West was in a state of terminal decline. Starting in the 1920s, Lovecraft became familiar with the work of the German conservative-revolutionary theorist Oswald Spengler, whose pessimistic thesis of the decadence of the modern West formed a crucial element in Lovecraft's overall anti-modern worldview. Spenglerian imagery of cyclical decay is a central theme in At the Mountains of Madness. S. T. Joshi, in H. P. Lovecraft: The Decline of the West, places Spengler at the center of his discussion of Lovecraft's political and philosophical ideas. According to him, the idea of decline is the single idea that permeates and connects his personal philosophy. The main Spenglerian influence on Lovecraft would be his view that politics, economics, science, and art are all interdependent aspects of civilization. This realization led him to shed his personal ignorance of then-current political and economic developments after 1927. Lovecraft had developed his idea of Western decline independently, but Spengler gave it a clear framework.
Lovecraft shifted supernatural horror away from its previous focus on human issues to a focus on cosmic ones. In this way, he merged the elements of supernatural fiction that he deemed to be scientifically viable with science fiction. This merge required an understanding of both supernatural horror and then-contemporary science. Lovecraft used this combined knowledge to create stories that extensively reference trends in scientific development. Beginning with "The Shunned House", Lovecraft increasingly incorporated elements of both Einsteinian science and his own personal materialism into his stories. This intensified with the writing of "The Call of Cthulhu", where he depicted alien influences on humanity. This trend would continue throughout the remainder of his literary career. "The Colour Out of Space" represents what scholars have called the peak of this trend. It portrays an alien lifeform whose otherness prevents it from being defined by then-contemporary science.
Another part of this effort was the repeated usage of mathematics in an effort to make his creatures and settings appear more alien. Tom Hull, a mathematician, regards this as enhancing his ability to invoke a sense of otherness and fear. He attributes this use of mathematics to Lovecraft's childhood interest in astronomy and his adulthood awareness of non-Euclidean geometry. Another reason for his use of mathematics was his reaction to the scientific developments of his day. These developments convinced him that humanity's primary means of understanding the world was no longer trustable. Lovecraft's usage of mathematics in his fiction serves to convert otherwise supernatural elements into things that have in-universe scientific explanations. "The Dreams in the Witch House" and The Shadow Out of Time both have elements of this. The former uses a witch and her familiar, while the latter uses the idea of mind transference. These elements are explained using scientific theories that were prevalent during Lovecraft's lifetime.
Setting plays a major role in Lovecraft's fiction. Lovecraft Country, a fictionalized version of New England, serves as the central hub for his mythos. It represents the history, culture, and folklore of the region, as interpreted by Lovecraft. These attributes are exaggerated and altered to provide a suitable setting for his stories. The names of the locations in the region were directly influenced by the names of real locations in the region, which was done to increase their realism. Lovecraft's stories use their connections with New England to imbue themselves with the ability to instil fear. Lovecraft was primarily inspired by the cities and towns in Massachusetts. However, the specific location of Lovecraft Country is variable, as it moved according to Lovecraft's literary needs. Starting with areas that he thought were evocative, Lovecraft redefined and exaggerated them under fictional names. For example, Lovecraft based Arkham on the town of Oakham and expanded it to include a nearby landmark. Its location was moved, as Lovecraft decided that it would have been destroyed by the recently-built Quabbin Reservoir. This is alluded to in "The Colour Out of Space", as the "blasted heath" is submerged by the creation of a fictionalized version of the reservoir. Similarly, Lovecraft's other towns were based on other locations in Massachusetts. Innsmouth was based on Newburyport, and Dunwich was based on Greenwich. The vague locations of these towns also played into Lovecraft's desire to create a mood in his stories. In his view, a mood can only be evoked through reading.