For Halloween

The idea of a ghost and the sense of the ghastly (two words from the same root) arise from a single source: the mystery and horror of death. Among all peoples and tribes, as far back as legends and other evidences go, the strange phenomenon of a lifeless body, the sight of a being recently full of motion and will and now present and absent at the same time, has inspired the notion that what has departed is the active principle — spirit — and that it may still have business to transact on Earth. The question then is, under what conditions can it do so and with what intentions, friendly or hostile? If it is to reappear, like and unlike itself, it must be heeded and if possible placated.
— Jacques Barzun, The Art and Appeal of the Ghostly and Ghastly, Introduction to Jack Sullivan, ed., The Penguin Encyclopedia of Horror and the Supernatural, 1986.