sunshadow21
Explorer
DMG, pg 5, 5th paragraph under "Part 3: Master of Rules". <-- basically says "You're the DM, you need to know the rules or where to find them if you don't".
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On the first part...yes, you need to be a human reference sheet if you want to be anything even approaching a great DM. You can get by with relying on players for stuff, sure, but you (general "you", again) will never be a great DM. This is fine for most groups (hell, probably all groups!), but it doesn't change the fact that a truly superior DM will know the game inside and out. And the real test is, as always, "Is everyone at the table having a good time?". As long as that answer is "HELL YA!, then keep on keeping on.However...
Anyway, I still stand by my earlier post. A DM should know ALL the rules in the game (including spells, abilities, etc). It's how much of this knowledge that is accumulated that really helps a DM run a superior campaign. Of course, "should know ALL" isn't a requirement for playing in a D&D game and having a good time. Hell, some of the best times I've had playing RPG's is when we don't know anything about a new game and are learning it, fumbling our way around the rules like newborn kittens. But, as time goes on, we learn the rules. The DM/GM/Ref/Whatever needs to step up more and learn more stuff. If he doesn't, he's nothing more than "just another player, rolling dice for the monsters".
I agree with the part above the line, but not the part below. Most of the time, the best place to find information pertaining to what the PC's are doing in the middle of the combat quickly and efficiently is from the players themselves, not from having memorized the rulebook. I as a DM cannot and will not try to memorize every possible thing that each PC is capable of; I especially will never reach the point where I will be able to pull random spell A seen once or twice in an entire campaign out of my head when I am trying to focus on the NPCs and the actions of the other players in addition to what the player whose turn is currently is wants to do. The players have to meet me half way if there is going to be any hope of getting through any combat half way efficiently; I don't expect them to memorize everything themselves, but they need to have good notes and be using their time between turns reasonably effectively so that when their turn comes around, they can answer most questions I might reasonably have with a reasonable amount of time.
I need enough knowledge to understand when I need to look something up myself right then and there or when what my players tell me is enough to work with at that moment, nothing more and nothing less. I don't have to memorize the entire Player's Handbook to be a good, or even a great DM; what I do need is to get a good feel for when I need to worry about the rules and when I can get away with not worrying about every little detail. Knowing details about what each PC brings to the table certainly helps, but details about every single thing every single PC can do is not something I would ever even consider trying. I am not the one running them for a reason; I expect the person whose whole stake in the game is through that one character to be able to learn how to run that character efficiently just as I work to run each NPC and encounter as efficiently as my skills as a DM allow. If someone genuinely needs help and is simply taking a bit longer than the rest of the party to fully learn everything, I can live with that, but if I don't see improvement after I and/or the other players have helped them as much as possible, it will start to get frustrating very quickly, and I will likely suggest (and have with a friend that is currently playing an archer in a 3.5 game but is consistently having difficulty understanding the math behind it) that they try a simpler class of the same type in order to get the underlying mechanics down before trying to deal with the more complex or option filled classes. If another player (or in the archer example above, the DM, as I am just a player in that game) is willing to help out and it doesn't take too much away from the game to do so, it doesn't bother me, but simply by stepping up to DM doesn't mean that I am agreeing to babysit every character and memorize all of their potential capabilities. It helps, and a good DM will learn from their experiences, but in my experience memorizing the rules doesn't matter nearly as often as memorizing with it's reasonably safe to fudge (or even ignore) the rules, and when it's genuinely important to get the rules right the first time, even if it means stopping the game for 5 minutes to do so.