Every once in a while I see references to house rules that emphasize the various “types” of magic. Those types are the parenthetical notes in the Players Handbook in the spell description sections; alteration, enchantment/charm, etc. They don’t really have any in-game effect (well, not until Unearthed Arcana was released, and even then it was half-hearted), and are seemingly included for flavor.
One natural inclination, however, is to think about breaking out magic-users (or, in Adventures Dark and Deep parlance, mages) according to specialty. Thus, we could have rules for conjurers, abjurers, necromancers, etc. Seems like a nice and neat system at first glance, and even Gygax stated that he was considering such a system for his never-completed Second Edition.
Yes, I did intend to have schools of magic based on the types of spells as you note above. The m-u would begin with one specialization, but at various points along the level progression ladder he could opt to add a new field or intensify his capacity in the original one. This was meant to make m-us interesting beyond the point where they could use 9th level spells, any diversion from specialization delaying the advanced spell level possession but adding new lower level spells of a new school.
Hence my own interest, vis-a-vis Adventures Dark and Deep.
The problem comes from the spells themselves. Here’s the breakdown of mage spells by type. These numbers are for the spells as they appear in Adventures Dark and Deep, so there are a few differences from this and the spells that appear in the 1E PH and UA, but the overall numbers should be close.
The problem is clear. Specialist alterers are going to have a huge advantage over, say, diviners, since an overwhelming plurality of mage spells (across all levels) are alteration-type spells. Necromancers are hardly given any advantage at all, since only 5 mage spells are classified as “necromantic”, and we don’t even see the first one– feign death— until the 3rd level of spells.
This problem, could, of course, be solved by simply adding more spells to balance out the various types. But this would actually be an enormous undertaking. The total number of first-level spells alone would balloon from 40 to a minimum of 144! And of course if the total number of mage spells are increased so dramatically, it hardly seems fair not to do the same for clerics and druids and the like. So from a purely practical standpoint, that doesn’t seem like a solution.