Late in the spring of 1976, Gary Gygax started work on a complete revision of Dungeons & Dragons. In Gygax’s TSR office, he and collaborator Tim Kask cut up several old copies of the D&D rules—copies much like the one that recently sold for $22,100 on ebay.

“The first day,” Kask recalled, “We sat with legal pads and dissected the elements of the game into various categories: combat, characters, magic, monsters, artifacts, spells, abilities, and on and on.”

They tacked rules clippings to bulletin boards, sorting them by category. “Then, category by category, we examined the game,” Kask wrote. “We looked for loopholes, inconsistencies and instances of what I’ll call ‘game-illogic.’ We looked at balance issues.” As they tinkered with hit-point totals and with the damage inflicted by weapons and spells, they playtested hundreds of battles.

After seven or eight days consumed by the work, Gygax and Kask produced a plan for Advanced Dungeons & Dragons.

They planned for three AD&D books that roughly matched the three booklets in the original box set. Men & Magic became the Player’s Handbook, Monsters & Treasure became the Monster Manual, and Underworld & Wilderness Adventure became the Dungeon Master’s Guide.

To actually write the books, Gygax needed years. He wanted hardcovers, but the expense of printing just one title would stretch TSR’s resources. Sales of the first title had to pay for the second, and the second for the third. If gamers chose not to splurge on pricey hardcovers—if they kept photocopying the original rules or if they turned to imitators—then TSR might sink.

Gygax chose to write the Monster Manual first. He figured that current players of the game could use new monsters with few adjustments. Also, the book’s design made writing simple. Every day, between other duties, Gygax would write monsters and throw the stats into a box for employee Mike Carr to collect and type.

When J. Eric Holmes’ introductory manuscript reached TSR, Gygax faced another decision. The new Basic Set would only take characters to level 3. Where should they go next? “Sending them into the morass of ‘Original’ D&D put us back on square one, with all the attendant problems of rules questions, misinterpretations, and wildly divergent play,” Gygax wrote in the March 1980 issue of Dragon. “Would it be better to direct them to AD&D, even if it meant throwing out what they had begun with the Basic Set and making them start a fresh? Faced with a choice between chaos and a clean slate, we opted for the latter.” This explanation comes from 1980, when Gygax had other reasons for claiming that AD&D stood as a different game.

In the summer of 1977, when TSR had a manuscript for basic rules and just outlines for a Player’s Handbook and Dungeon Master’s Guide, did Gary plan to create incompatible games?

He made a bid for compatibility. “Pieces and parts of the various components of AD&D were grafted into the Basic Set rules manuscript so that D&D would be more compatible with the Advanced game. Readers were directed to AD&D throughout the Basic Set.” His sales plan for the AD&D Monster Manual depended on players using it in their original D&D games.

But Gygax also expected differences. He and Kask had already tweaked some spells, damage, and hit point numbers. Because the Thief class highlighted the inconsistency where non-humans could treat their race as a class or could adopt a class, Gygax probably planned AD&D’s complete separation of race and class all along.

In a 2005 comment, Gygax wrote that he never intended the Holmes Basic Set to serve as in introduction to AD&D, and that he never intended to meld the two games.  But after decades of saying that AD&D was a separate game, perhaps his claim pushed aside any memory of his original plan. I suspect that if basic D&D had started as something more than introduction, TSR would have released an Expert Set in 1978. Instead, the expert rules came in 1981 when TSR needed them to bolster a legal case.

In the end, AD&D never proved as different as Gygax claimed. His new version of D&D remained roughly compatible with the original. Supposedly, AD&D featured strict rules while original D&D featured room for customization, but everyone—even Gygax—changed and ignored AD&D rules to suit their tastes. Later, Gygax wrote, “I just DMed on the fly, so to speak, and didn’t use the rules books except for random encounters, monster stats, and treasure.”

Next: Why Gary Gygax claimed Advanced Dungeons & Dragons was a different game