H. P. Lovecraft believed that the oldest and strongest fear of humankind is fear of the unknown. This belief was an important force behind the idea that he gradually developed over many years that the earth was once inhabited by a race of beings from another world or dimension who, while having lost their hold on earth, are waiting to enter again. This is the major theme in “The Dunwich Horror.”
This idea develops slowly as the story unfolds. Dr. Armitage has realized that “unseen things not of earth—or at least not of tri-dimensional earth—rushed foetid and horrible through New England’s glens, and brooded obscenely on the mountaintops.” Old Whateley on his deathbed tells Wilbur that only the beings from beyond, the Old Ones who want to come back, can make the monster multiply. The Necronomicon relates that the Old Ones broke through long ago, and they shall break through once again.
Lovecraft was indebted to the English writer Arthur Machen (1863-1947) for the inspiration of this idea, but he carried the idea much further and in a different direction, for although Machen’s otherworld is populated by a mixture of little people and nature deities (sometimes fearful), Lovecraft’s otherworld, or dimension, is completely terrifying and threatens the continued existence of this world. Lovecraft built up these ideas into an entire body of myth known as Cthulhu Mythos. The names mentioned in the Necronomicon, such as Yog-Sothoth, Cthulhu, and Kadath, are beings or places important in the myth.
An interesting and related idea in the story is the ominous feeling imparted by great age. The beings from beyond are described as the oldest things in or around earth. Old Whateley is extremely aged, and the rapid aging of Wilbur is emphasized. The entire village of Dunwich is seen as old, decadent, and unsettling in appearance, and the stone circles (where evil rites are practiced) are of great antiquity, going back at least to Indian times.