Excellent post! Of course, this being the internet, I am contractually obligated to nitpick one tiny thing out of all the other, great stuff you said.
I don’t agree that most good DMs necessarily come up with systematized heuristics. Certainly many DMs do, and many of them are good. But many of them are bad, and many good DMs stick to ad hoc, case by case adjudication.
Take your Silence on a Swarm of Bats example (and set aside the fact that the rules of 5e at least are actually quite clear on what happens in that scenario). Is the game really better served by ruling “no effect” simply because the DM uses that heuristic consistently, than it would be to rule based on their (possibly incomplete) understanding of bats? I don’t think so.
Heuristics like this can be useful, but they can also be inflexible. I think it’s a good DM who recognizes when to employ heuristics and when to go with ad hoc rulings.
So what I was thinking about when I wrote the thread was the following-
1. In the world of corporations, it is a truism that you'd rather deal with a consistent and bad law, than an inconsistent and arbitrary law that might occasionally be good. When people first hear this, they are often surprised; by definition, bad laws are bad! But consistency is such a virtue that the consistent application of "badness" is preferable to arbitrary application of occasional "goodness." You can plan for, contract around, avoid, and have settled expectations regarding the bad law. On the other hand, when the law is arbitrary and inconsistent, you got nothing. Any upside for the company is negated by the inconsistent application- since the company can't assume the good application, and can't plan for the bad application, it's in the worst of all possible worlds (or, at best, it always has to be planning for the absolute worst application). This is a long way of saying that consistency is an overlooked virtue.
2. I think that there are two general types of
ad hoc rulings- those that are using unexamined heuristics (type A), and those that are inconsistent, arbitrary, and capricious (type B). Type A rulings are those made by DMs that believe that they are employing a case-by-case method of adjudication, but are, in fact, using certain internal rules of thumb (heuristics) in order to achieve relatively uniform results. They may not have interrogated their own internal processes very much at this point in order to tease out what it is they are doing, but they are in doing it. Type B rulings are those that are truly
ad hoc; there are no heuristics being employed by the DM, and every adjudication is a new walk in the park, the result being unpredictable and unknown.
3. Moving from 1 & 2, I look to the players at the table. The consistency of adjudication by the DM matters greatly to the players. A DM that is predictable in the results (at least in the process) invites the players to perform to a certain standard; inconsistent and arbitrary rulings are more frustrating to players than "bad" rulings. Using the Strict/Permissive binaries above as exemplar heuristics, a DM using a strict heuristic will likely foster a table that sticks to "by the book," while a DM using a "permissive" heuristic will likely foster a table that goes beyond the rules more; a DM that inconsistently applies
ad hoc rulings, however, will most likely engender that type of "mother may I" resentment at the table, as the players will never be certain how the DM will rule.
4. As with most of my posts, I present the typology mostly for discussion. I don't think these categories are all-encompassing or that most people fit neatly within only one of them. Moreover, the main purpose is to get people to think about, well, thinking. Too often most DMs assume that every ruling they make in D&D is an
ad hoc ruling; unlike other games, there is just the division of rules and rulings, and it is not very clear what factors the DM is supposed to use to make those rulings (unlike other games, which make it explicit with guidelines like, 'The GM is a fan of the players'). I think it is a helpful and important exercise for DMs to interrogate the assumptions and heuristics that they use when making rulings. I know that it was a few decades in before I even started thinking about it!