Authors of Gothic works were operating in the Age of Reason. Often, at the end of a haunted narrative, they provide perfectly rational explanations for the seemingly supernatural elements of the story. Walter Scott voiced his distaste for this practice: "We disapprove of the mode introduced by Mrs. Radcliffe . . . of winding up their story with a solution by which all incidents appearing to partake of the mystic and the marvelous are resolved by very simple and natural causes . . . We can . . . allow of supernatural agency to a certain extent and for an appropriate purpose, but we never can consent that the effect of such agency shall be finally attributed to natural causes totally inadequate to its production."
But to read the supernatural in Radcliffe through Scott, whose expectations are closer to our own, is in some ways misleading. There are dimensions of ghostliness in the work of Radcliffe and her followers that exceed and complicate the opposition of natural and supernatural, imitative and purely imaginary, presupposed by Romantic criticism of the "explained supernatural." The most obvious residue of the spiritual after all supposed apparitions have been cleared away is Providence. . . The bizarre coincidences that are produced to explain the supernatural are not just a technical convenience, as Scott asserted, but evidence of a higher supernaturalism that ensures every "accident" has its rightful place in the schema of Divine Justice.
Source:
E.J. Clery, "The Supernatural Explained," The Rise of Supernatural Fiction 1762-1800 Cambridge; Cambridge UP, 1995: 106-171.