As I don’t have copies of the AD&D corebooks immediately available at my disposal, I’m pulling the text from OSRIC; if the actual text is substantially different and OSRIC wrong on this, by all means, let me know, cuz that seems like a big deal! I know I said I would look at Holmes in part 2, but I think I will make it 1.5, since it bridges the gap between OD&D and AD&D, with B/X kinda off in its own direction.
In OD&D, and presumably B/X*, wizards can go down to SpellCo and just buy a level’s worth of spells in a single volume. The magic user isn’t going to be able to learn all of those, of course, but they physically HAVE those spells. There’s no need to scrounge towers for lost arcana, because you already have access to all of the vanilla spells for your caster levels.
In AD&D, however, we start to see thematically Vancian magic emerge.
“A beginning magic user character will know four spells. One of these will automatically be Read Magic. The second spell should be chosen by the player from the list of first level spells, and the last two should be determined randomly from the list of first level spells.” – OSRIC, p 16
So, now we have the assumption that a Magic User at 1st level is someone who has completed his apprenticeship and has access to a small assortment of spells that his master has presumably given him; his student’s spellbook will contain Read Magic and 3 other spells.
Here’s what OSRIC says about scrolls:
“Spells are also sometimes found written on scrolls. It is not
possible to memorise a spell from a scroll, although magic
users and illusionists may copy the spell from the scroll into
their spell books, if they understand the spell. This process
always erases the scroll. This is the primary means by which
magic users and illusionists will acquire new spells for their
Alternatively, the spell may be cast directly from the scroll, in
which case the scroll is erased as the spell is cast. In this case,
it is not necessary for the caster to know the spell beforehand,
and indeed it is possible to cast a spell from a scroll even if
the caster does not know the spell or is of insufficient level
to use the magic.” – OSRIC, p 35
So, the Dungeon Book from Holmes is gone, but using scrolls to learn new spells is in. As they’re written in magic, presumably Read Magic is necessary for a chance to enter them into your spell book.
“Read magic is normally the fi rst spell in every magic user’s spell
book, and its mastery is the fi rst task of every apprentice. The
spell allows the caster to read magical writings (other than
his or her own, of course, which are always intelligible to the
Unless the writings are cursed, reading magical script does
not normally activate the magic formulae described therein—
reviewing a scroll prior to casting from it does not, for instance,
actually cast whatever spell is written upon the scroll. Once the
magic user has read a particular set of magical inscriptions by
use of this spell, the spell is no longer needed to re-read the
writing at a later time.
The reverse of the spell allows the magic user to make magical
writings indecipherable for the spell’s duration, and is cast
upon the writing rather than upon the caster him- or herself.” – OSRIC, p 97
While it is still necessary for using scrolls, the Read Magic’s greater purpose now becomes to translate scrolls and stolen spellbooks and enter those new spells in your spellbook. Magic Users can no longer simply buy a book for 2000 GP x spell level to unlock a new level’s worth of spells as in OD&D or Holmes, and unlike B/X, where Magic Users ONLY know their spells selected when leveling up, Magic Users can theoretically learn multiple spells based on the MU spell Acquisition Table. Since all Magic Users have Read Magic, and since they do not have B/X’s restrictions, it is no longer a question of forever sacrificing a spell slot for the ability to use scrolls.
To learn new spells in AD&D, Magic Users must cast Read Magic, attempt to understand the spell (MU Spell Acquisition Table), and, if successful, scribe the spell in to his spellbook. Finally, magic in D&D is starting look truly like something out of Dying Earth!
*Holmes, anyway; in B/X, I believe you can replace your spellbooks, but you do not have access to more spells than those matching your current level’s Spell Per Day table, i.e. you can’t know 4 1st level spells unless you can cast at least 4 1st level spells.