Suppose you were told there was a tiger in the next room: you would know that you were in danger and would probably feel fear. But if you were told ‘There is a ghost in the next room’, and believed it, you would feel, indeed, what is often called fear, but of a different kind. It would not be based on the knowledge of danger, for no one is primarily afraid of what a ghost may do to him, but of the mere fact that it is a ghost.
Lewis formulated this opposition by drawing on Rudolf Otto's 1917 THE IDEA OF THE HOLY. However, a much earlier distinction appeared in a 1826 analysis by Gothicist Ann Radcliffe, where she distinguished between "terror" and "horror." This analysis, later given the title "On the Supernatural in Poetry" by an editor, isn't particularly well-organized. In essence, Radcliffe-- whose Gothic novels depended on suggestion rather than explicit gore and gruesomeness-- has her principal character argue that "terror" is a much subtler and finer emotion than "horror," which is all about the explicitness. Here's her most definite statement on the difference:
Terror and horror are so far opposite, that the first expands the soul, and awakens the faculties to a high degree of life; the other contracts, freezes, and nearly annihilates them.
This doesn't really clarify the matter all that much, but a later section makes clear that Radcliffe equates the sublimity of terror with that of the merely suggested, the merely imagined. When an interlocutor asks the speaker what he thinks about Milton's line, "On his brow sat horror plumed," the speaker essentially co-opts MIlton's use of the word "horror" for the speaker's (and Radcliffe's) idea of "terror:"
As an image, it certainly is sublime; it fills the mind with an idea of power, but it does not follow that Milton intended to declare the feeling of horror to be sublime; and after all, his image imparts more of terror than of horror; for it is not distinctly pictured forth, but is seen in glimpses through obscuring shades, the great outlines only appearing, which excite the imagination to complete the rest; he only says, ‘sat horror plumed ;' you will observe, that the look of horror and the other characteristics are left to the imagination of the reader; and according to the strength of that, he will feel Milton's image to be either sublime or otherwise.
According to this site, Radcliffe was not a fan of explicit gore, and wrote her book THE ITALIAN (which I have not read) as a pointed response to the excesses of Matthew Lewis's 1796 Gothic novel THE MONK (which I have read-- meaning that I can personally attest that the Lewis book definitely does not hold off on "distinctly picturing forth" its ghastlier scenes).
If there are any significant parallels between the formulations of Ann Radcliffe and of C.S. Lewis (by way of Otto), it would seem to be the mutual attempt to define the nature of fear based in purely physical causes. Lewis' tiger can only inspire fear because there's no deeper concept to be understood about it, save that it's an animal capable of killing a human being. This is only a partial parallel to Radcliffe's use of "horror," which "contracts, freezes, and nearly annihilates" both the soul and the faculties. But her contrast to "terror," like Lewis' contrast to the "uncanny" feeling of seeing a "ghost," is pretty clearly based upon the familiar body/mind duality, which poet Octavio Paz more aptly rendered into a duality between "body" and "non-body" (or as I once called them, "corporeal" and "non-corporeal.")
To further complicate the matter, although Lewis is to some extent addressing the question of different phenomenal presences in different situations, Radcliffe apparently has no interest at all in aligning either "terror" or "horror" with any type of phenomena. Though she doesn't mention THE MONK in the above essay, it's plain that she would class it as a work of "horror" simply because it "distinctly pictures forth" all of the unseemly situations it includes-- ranging from the monk Ambrosio's (naturalistic) incestuous union with his own sister, to his (marvelous) doom at the hands of a demon, who flings Ambrosio's body from a great height and allows the monk to perish in agony. If anything, Radcliffe's distinction of "distinct" and "indistinct" is closer to my distinction between "clean" and "dirty violence" in this essay:
I said in an earlier essay that I would address the differing "intensities" of violence in fiction, by which I meant what I called "clean violence" vs. "dirty violence." These are NOT meant to be covalent with my versions of Twitchell's preposterous violence and its unnamed opposite. I refer to the "intensities" of clean and dirty because they are determined purely by how intensely the work does or does not present scenes of violence. As I see it preposterous violence and its opposite are not determined by intensity of effect but by narrative function.
Again, the parallel is still not exact. Still, just as the proponent of "suggestive terror" does not want to "freeze the soul/faculties" of the reader by bringing in gross effects, the proponent of "clean violence"-- my principal example being the 1977 STAR WARS-- is also seeking to avoid grossing out the audience, albeit for a very different aesthetic purpose.
Now, my own definition of "dread" moves away from Lewis's example of a "ghost:" to anything covered by my Ten Tropes, which occur in both naturalistic and uncanny forms-- the first forms inspiring only "fear," while the second may inspire fear but more importantly inspires "dread" as well. The latter comes about because even though both forms obey the laws of causal coherence, the uncanny forms violate the law of intelligibility. In the interest of further defining the process through which intelligibility is violated, I'll devote the upcoming essay JUDGING DREAD PART 2.