Fifth Element said:
According to ancient Gygaxian wisdom, you can deviate from the rulebooks all you want but if you do so, you are not playing D&D.
Edit: typo.
I'm sorry, but I think this is a false statement. If this is drawn from the preface to the 1E DMG, then you are (perhaps quite unintentionally) misrepresenting what Gary was saying. I'll quote the relevant passage:
1E DMG said:
The danger of a mutable system is that you or your players will go too far in some undesirable direction and end up with a short-lived campaign. Participants will always be pushing for a game which allows them to become strong and powerful far too quickly. Each will attempt to take the game out of your hands and mold it to his or her own ends. To satisfy this natural desire is to issue a death warrant to a campaign, for it will either be a one-player affair or the players will desert en masse for something more challenging and equitable. Similarly, you must avoid the tendency to drift into areas foreign to the game as a whole. Such campaigns become so strange as to be no longer "AD&D". They are isolated and will usually wither. Variation and difference are desirable, but both should be kept within the boundaries of the overall system. Imaginative and creative addition can most certainly be included; that is why nebulous areas have been built into the game. Keep such individuality in perspective by developing a unique and detailed world based on the rules of Advanced D&D. No two campaigns will ever be the same, but all will have the common ground necessary to maintaining the whole as a viable entity about which you and your players can communicate with the many thousands of others who also find swords & sorcery role playing gaming as an amusing and enjoyable pastime.
It is important to keep a few things in mind. The passage just before this says that ability scores should represent roughly the same thing in most campaigns, spell and magic item effects should be fairly consistent, etc. so that it is easy for players and their characters to transition from one campaign to the next, and so that a network of players can be built up which will allow various DMs and players to all be speaking a common language; eventually "grand tournaments" could arise from this structure. "Network externalities"? I think Gary already thought of it.
Also keep in mind that the above was written as the preface to the same book that includes rules for combining D&D with Gamma World and Boot Hill, and written by the guy who wrote
Expedition to the Barrier Peaks.
So what Gary seems to be saying is more along the lines of "If you redefine the Strength table so that 3 means you can kick over a mountain and 18 means you can punch a black hole into the cosmos, or you reset the attribute range for PCs to go from 1-1000 (but keep the values as they are... so that an average character hits for +485 damage or something), or you say that magic swords can only be used by half-dwarf half-giraffe mage-titans, etc. then you've gone so far beyond the assumptions and framework of the game that it's not AD&D anymore, and so you have isolated yourself from this network of gamers we're building and have overturned my fundamental (and wise) design philosophy."
But he is
not saying that if you make up a house rule you're not playing AD&D. It was designed to allow that, in fact! Gary states that he purposefully leaves the rules nebulous in certain areas so that everyone can have their own rulings and procedures and world. He says that difference and addition are desirable. His concern is with morphing it into something so unrecognizable that it could no longer be considered AD&D. Hence the concern is not with modification, but with totally altering the underlying assumptions and framework. In which case I think it would be fair to call it a different game.