Sure. I think S&S has to be understood as encompassing more than just REH. I just get a bit bemused by pronouncements that such-and-such is not part of S&S when REH stories are replete with such-and-such.I think you've acknowledged that you aren't familiar with Lieber et al. ("I've never read Leiber and haven't read much Moorcock.") While REH's Conan is, of course, S&S, we can't single-source a genre. The difficulty in making pronouncements about S&S as a genre is just that- at a minimum, it encompasses REH's Conan, Lieber's Fafhrd & Gray Mouser, and Moorcock's Elric- which have similarities, but also disparate elements.
In that sense, S&S is very much like film noir, in that the genre borders are difficult to understand.
I get the impression, by reputation, that Leiber's stories involve less moral/honourable protagonists than REH's Conan. Though I don't know if that's true.
I'm also not sure if The Dying Earth should be included in S&S or not - Vance definitely presents moral/honourable conduct in a very different light from REH, but this feeds through to the world in general. The whole thing is cynical in a way that Conan isn't, and that I think Moorcock isn't either (though some Moorcock characters might be).
I fully agree with what you say about "hardboiled"/pulp detective fiction. I had almost made a post contrasting And Then There Were None with The Maltese Falcon, but held back because I've never actually seen the 1945 Christie film.But I wanted to concentrate on something you said separately which I completely agree with, albeit perhaps I might quibble with a little bit of the phrasing given we are talking about a literary genre:
But as I see it the main contrast between S&S and JRRT-ish fantasy is that the former is modernist, even sometime existentialist - it presents the world as inherently lacking in value, and it is the action of the protagonists that imposes truth and meaning on the world - whereas JRRT-ish fantasy is conservative - it posits a world laden with meaning, and the path of heroism is identifying that meaning and having the faith and courage to act in accordance with it.
I would start by saying that S&S is not modernist in the literary sense, although it is modern. Just a small definitional quibble, given that I wouldn't want people to confuse the genre and think that Howard and Lieber are writing in the same vein as Joyce and Faulkner. Sure, a person can make the argument that REH, Lieber, Moorcock et al. are part of the pre-war proto-modernist movement (Conrad, et al.) but that's a topic for another time- anyway, I think that it would be better to say modern.
And here, I think you are exactly correct. S&S is, essentially, modern fantasy, while high fantasy (Tolkien, et al.) is essentially small-c "conservative" fantasy. Most Tolkien-esque fantasy has, in addition to the usual "high magic," the following:
A. A world (way of life) that is either under attack and needs to be defended from outside ("evil") forces, or a world that has succumbed to those evil forces and needs to be restored.
B. A protagonist who is a protagonist of right. Whether it's bloodline (Harry Potter), or destiny (Taran), or there's a hidden king somewhere or other (Strider/Aragorn), there is always a protagonist that that is awesome because s/he was just born that way.
I think you are 100% correct in noting that S&S tends to eschew these conservative aspects of high fantasy. In fact, if I had to compare it to any genre, I would probably say it is most similar to the "hardboiled," - another pulp genre that is modern, and rejected the older detective approach (Christie, Doyle). In hardboiled, you usually have the characters dealing with a modern and industrial system that choose to operate outside of the system, rendering them morally ambiguous at times (anti-heroes), even when they act in moral fashion.
I think I might see more continuity between this "post-Victorian" style and modernism in the stricter sense than you do, but that seems pretty tangential to the main point. My criticism is amateur whereas my philosophy and social theory is professional, and by "modernism" I'm meaning more in thematic or politico-social terms than as an artistic movement. (And I certainly don't want to say that REH is an author who, in either technical or artistic terms, is on a par with (say) Hemingway; on the other hand I think the authors of WotC D&D books could learn a lot from reading REH and giving their work a good edit!)
I'll finish with a paragraph (or two, as it turns out) that is (are) probably more controversial (vis-a-vis you and probably vis-a-vis other posters too). I think that one problem with trying to "do S&S" using D&D is that D&D has already muddied the waters quite a bit. On the one hand, D&D is replete with the tropes of "high fantasy"/conservative romance - paladins, many clerics, Tolkienesque Elves and Dwarves and Orcs, many non-Planescape readings of the alignment system, etc.
On the other hand, the typical interpretation of dice rolls in D&D (as best I can tell from entirely non-scientific observation) is that they represent the workings of a cold, impersonal universe. Gygax's protestations to the contrary (eg in his discussions in his DMG of the fact that higher hp, and better saving throws and other abilities, represent the interventions of supernatural forces in favour of the PCs) never really seem to have taken hold. I'm not even sure Gygax believed them in his actual play, despite having written them in his rulebook. And this is S&S through-and-through: a universe without providence, and in which "fate" is just a label for what a person makes of him-/herself. I think this can sometimes make it a bit hard to focus on exactly what needs to be done to D&D to more purely align it with S&S play.