AbdulAlhazred
Legend
There is really almost nothing. I mean, I am thoroughly familiar with AD&D (both editions) as I started playing before it was even written, and all my books are first printings (like, my 1e Monster Manual actually is missing some of the art which didn't make it into the first print run). The 1e DMG is entirely written by EGG, and he does have a chapter where he rambles on about how maybe social structure works in a medieval society. None of it is rules, per se, it is just a bunch of very amateur writing on the subject. I mean, I can claim no greater expertise than Gygax on the subject, but even I can easily spot a bunch of pretty silly statements, and on the whole his treatment is highly colored by modern conceptions and tropes, at best. That's basically it.I don't need specificity, just some examples to look at. Remember, my "oldest" D&D experience was 3.5. I don't have played anything older, and unless there is a good reason to do so, I don't plan to, either.
I don't know anything about 2e and earlier rules. And the ones I know I don't like it. Like that one about f*cking your players if they take time buying stuff. Are you talking about that kind of rules?
I mean, other than that, what is there? There's some rules covering the hit points, pay, etc. of ordinary citizenry, but it is all completely gamist and doesn't have any association with realistic medieval type economics or society, whatsoever. There's an overland exploration and (generously) orienteering rules section. I think his rules on consumption of rations might be in the right ballpark, but all the rest of it is simply "here's some fun rules for playing D&D overland" and doesn't really connect with reality in any particular way. At best it is abstract enough that we cannot really say it is either realistic or unrealistic. It works modestly well as a part of the game, and that is, IMHO, all that was intended.
There's a level of realism in AD&D that is basically: If you take a fall, you will be hurt. That's about as detailed and realistic as it gets. Rules for things like diseases, healing, fatigue, etc. are mostly tropes and often fairly misinformed, but generally meet players expectations, which is all they really NEED to do. Take horses for example: magically D&D horses extend your overland mobility greatly, but in the real world this is, at best, highly situational. Sure, riding is 'faster' than walking, sort of. I mean, I don't think D&D SHOULD have rules for realistic use of horses, it would be tedious and require a lot more detail than the equipment lists can give you. Still, no attempt at realism was made, and I doubt Gygax even knew one end of a horse from the other (again, I'm not a huge expert myself, but I have owned a few horses and ridden them at least).
Obviously people's definition of verisimilitude is going to differ, but my diagnosis of D&D generally is it caters to fantasy tropes first, and then makes a few concessions to popular ideas about 'how things are' where that doesn't interfere too much with fun game play.