Casting Spells

What actually happens when a AD&D™ magic user casts a spell?

According to the DMG1 p.40 and PHB2 p.81, the process started some
time previously, when the mage spent 15 minutes (in AD&D2, 10
minutes) times the level of the spell "memorizing" it from their spell
book. This normally requires that the mage have their spell books, peace
 and quiet, and be well rested. DMG1 p.40 gives a table of the amount of
 rest (normally sleep) required before this can be done, according to
the level of the spell to be memorized. One some DM's planes, the mage
may find that this needs to be uninterrupted and comfortable sleep (this
 can be very inconvenient on wilderness adventures, though a good way of
 getting out of standing watches!). If the mage is of a race that does
not sleep (liches are a common example), then some form of meditation is
 usually required instead. On some planes, even those mages that do need
 sleep may be able to memorize spells after a suitable lengthy period of
 meditation. This has the advantage that, while it is quite hard to
sleep more than once a day, it is possible to meditate several times a
day. For 1st or 2nd level spells, where only 4 hours rest are required, a
 Wizard might manage to sleep 4 hours, spend 2 hours memorizing his 4
first level spells, and then cast them, twice a day, giving eight first
level spells a day (for example when desperately Mending his employer's
charger's barding that his pet Rust Monster half-ate!). With periods of
meditation, this could be increased to 12 or even 16 first level spells
in a day, though few mages would be able to maintain this for long.

On some planes, the mage may find that nothing of any significance
can be done between sleeping and memorizing spells (getting up, having
breakfast, but no spell-casting or traveling). If this stricture does
not apply, then there is no obvious reason why the mage cannot memorize a
 spell, pause briefly to cast it, and than rememorize it. The spell
numbers given on PHB1 p.26 (PHB2 p.30) are maximum numbers of spells
memorized at any one time. Unless the mage is on a plane where this is
also the maximum number of spells that may be memorized during any one
day, then this allows a mage to cast a great many spells per day, as
long as they are low level spells and the mage need do nothing else. For
 example, even working only an 8 hour day, any mage could cast 32
Mending spells this way, or ten Dispel Magics.

For an 18th level mage, rememorizing their entire spell list takes
nearly 35 hours (just over 23 in AD&D2). It is obviously ridiculous
for a mage to expect to do this in one stint, even if they have had 12
hours sleep previously. I would advise mages not to exceed 8 hours spell
 memorization (32 spell levels in AD&D1, 48 in AD&D2) except in
emergencies, as magical overwork in well known to cause nervous
exhaustion.

On some planes it is possible to "demote" spells: instead of
memorizing one of your allowed number of high level spells, you can
memorize an extra spell of a lower level. This can be very handy if you
have a lot of useful spells at one level, and few at some higher one. Of
 course there are some mages who will just memorize 13 Fireballs when
they are 12th level, but then what do they do when they need to teleport
 away in a hurry? The loss of flexibility in having many copies of one
spell is almost never worthwhile, unless you are certain of exactly what
 situation you are going to meet. It is usually better to have a wide
range of options than to be able to do one thing many times. It should
be born in mind that demoting a spell represents a reduction in total
power: you are carrying less spell levels of spell around with you. On
the other hand, when what you really need is a Rope Trick, any number of
 third or fourth level spells are not going to help. Spell demotion is a
 useful addition to the techniques of a careful and thoughtful mage, and
 it is always worth experimenting to see if it is possible on your home
plane.

But what is actually happening when a mage "memorizes" a spell? Since
 the mage already had already learnt the spell (and it was already
counting against their maximum number of spells per spell level for
their INT), and indeed the mage can "memorize" multiple copies of the
same spell, it is evident that "memorize" is not really the correct
verb. "Store" or "charge up" would be better, as PHB2 p.81 makes clear.
By using their spell book, the mage slowly summons magical energy
("mana") and shapes it into the spell, storing the result in their mind
ready to be released rapidly in combat by a few words and gestures. Just
 what is involved in this process, apart from the spell-book, peace,
quiet, and a well rested mage, is not explained. I would expect that it
also involves a good deal of mental gymnastics, repetitively chanting
the words, and probably some ritual equipment, incense etc. All of which
 tend to attract the attention of passing monsters! The stored magical
energy of all the spells memorizable by a high level mage is
appreciable, and on many planes this is sufficient to cause them to
detect a faintly magical. This it is only faintly, compared with the way
 they would register if all the spells were cast, is because the flow of
 mana from a memorized spell is small (after all, they do not leak away,
 even if it is months since they were memorized), while in a cast spell
it is quite large, and is normally much increased by mana flows summoned
 from other planes.

It states in PHB2 p.81 that a mage cannot get rid of a memorized
spell, in order to replace it with another one, without casting it. This
 seems a very unfair rule: while casting a spare Fireball to get rid of
it is merely inconvenient (particularly in built up areas, or confined
spaces underground), some spells require extremely expensive components
to cast, or age the caster or even lose them points of constitution. If
this rule is strictly applied on a plane, then local mages should take
great care before memorizing such spells that they are really going to
require them. The problem of the effects of the spell going off (such as
 unwanted Fireballs) are easily avoided: according to PHB2 p.85 if the
spellcaster's concentration is disrupted during spellcasting, for
example by being struck by a weapon or failing a saving throw, then the
spell is wasted in a fizzle of useless energy. This effect can be easily
 and painlessly duplicated out of combat by starting to cast the first
segment of a spell, and then pausing part-way through to eat some nuts
and daydream about the innkeeper's daughter. The spell that you started
will be wasted, without any loud or disruptive magical effects. More
seriously, I would suggest that any referee allows a mage to
deliberately dump a memorized spell, simply allowing the structured mana
 they have stored to leak away harmlessly, rather than casting it.
Since, as discussed below, the mana stored by the mage is small compared
 with that which the cast spell will summon from other planes once cast,
 there should be no deleterious side effects to this, nor any use of
expensive spell components.

When the spell is cast, the magical symbolism of the words of the
verbal components, the gestures of the somatic components, and the
magical influences of the material components reinforce the structure of
 the spell, trigger it to activity, and direct it to the particular
target the mage is casting it at. (On most planes, the final decision of
 targeting is made in the last segment or so of the spell, allowing the
Fireball to be shifted a little if the front rank have advanced during
the intervening few segments. On others however, the targeting must be
decided the beginning of the casting, which requires considerable care
and forethought by the mage.) The spell then uses its stored mana to
reach out to one or more other planes, and tap the potential difference
between them, or between them and the Prime Material plane on which it
is cast. The planes used are normally the Positive and/or Negative
Material Planes, depending upon the spell. (For fire or heat spells, the
 Elemental Plane of Fire is used instead or as well; for wind or
lightning spells, the Plane of Air; for water or acid spells, the Plane
of Water; and for stone spells, the Plane of Earth. ) This mana flow
involves much greater amounts of mana than those originally stored by
the mage during memorization. (Psionics, on the other hand, does not
appear to involve summoning mana from other planes. The huge amounts of
mana that must be expended directly, and very rapidly, by a psionic
creature explains why on most planes humans are incapable of psionics,
and even on those planes where they can, the necessary talent is very
rare. Psionics is normally confined to highly magical creatures such as
Mind Flayers, Demons, or Lammasu.) This flow of mana from other planes
continues for as long as the spell lasts, and this is what is detected
by a Detect Magic spell.

It is evident from many separate sources (eg. spell memorization and
(most) casting times) that the initial amount of stored mana required to
 cast a spell is directly proportional to its spell level, ie an eighth
level spell requires twice as much mana as a fourth level spell. On the
other hand, the amount that can be done with a spell seems to increase
much more rapidly than that (compare similar spells of different levels,
 eg the various Bigby's Hand spells). After a good deal of
consideration, we have come to the conclusion that the mana summoned
from other planes by a spell once it has been cast roughly doubles for
every two spell levels of the spell (1st: 1, 2nd: 11⁄2, 3rd: 2, 4th: 3,
5th: 4, 6th: 6, 7th: 8, 8th: 12, 9th: 16). Another factor that is
important for a spell is the level of casting, ie the experience level
of the caster who cast it (or equivalent if the spell came from an
item). We belive that increasing this does not correspond to increasing
the amount of mana (ie a Fly spell cast by a 25th level mage does not
detect as being any more magical than on cast by a 5th level mage), but
rather to the skill and accuracy with which the spell was constructed,
and thus to the efficiency with which the mana is made to do work. (This
 provides a good rationale for the dice limits on variable damage spells
 in AD&D2: you can't get more than 10D6 out of a 3rd level spell,
even if you connect it directly to the hottest part of the Plane of
Fire, and even getting 10D6 takes a good deal of skill.) Note that it is
 perfectly possible for an item to cast a high level spell at a low
level of effect, eg. a Wand of Force casting Wall of Force at 6th level,
 which suggests that the skills involved in casting a spell at a high
level of effect, and those involved in being capable of memorizing it in
 the first place are different, though they are learned together by
magic-users.

If the flow of mana is interrupted, either by the spell being covered
 by an area of Anti-Magic, in which the flow of mana from other planes
is prevented, or by the brief glitch or pulse of mana of a Dispel Magic,
 then the spell collapses. If the spell is one from a permanent
continuous magical item, such as a +1 Sword or a Ring of Invisibility,
then the structure of the spell is built into the item, along with a
sufficient store of mana to restart it, and it will start to function
again after it has been dispelled/moved out of the Anti-Magic area. This
 normally takes 1 round (D4 rounds in AD&D2) for the spell to
recover after the jolt of successful Dispel Magic, but only a segment or
 so after the power supply returns on leaving an area of Anti-Magic. Of
course, if the spell was one cast from an item, it acts like any other
cast spell, and simply collapses, with no item at the center to maintain
 its structure.

There are planes where memorization is unnecessary, and a mage can
cast any spell that they know, subject to a maximum number of spells per
 day which matches the maximum number which can be memorized at once on
conventional planes. (This sort of freedom is more commonly found among
clerics of major local religions, where the spell is supplied by the
cleric's deity when it is asked for in combat, rather than being granted
 earlier during prayer and stored and subsequently cast directly by the
cleric. On occasion deities who do not, presumably, have the time or
inclination to do this for all their clerics may grant this as a special
 boon to favored high priests, or during a particular quest or temple
defense or holy war.) On most such planes it is possible to memorize
spells, and prudent to do so if you expect to be traveling off-plane,
but not necessary. This can be extremely useful, as it avoids the
difficult decisions as to which spells to take, and avoids the necessity
 to spend a great deal of time memorizing spells before (and during)
adventures, usually much to the relief of the non-spellcasters in the
party. However, there is a hidden disadvantage: in a rapid combat, the
mage will find it even more difficult to decide which spell to cast, and
 may end up doing nothing, or something over-ingenious. This can be a
particular problem for those high-level, high-intelligence mages
fortunate enough to know a great many spells, especially since
high-level combats tend to be decided quite rapidly. If visiting such a
plane, some mages may find it advisable to memorise spells as usual,
rather than disrupting their well-practiced combat reflexes. Out of
combat, it is a great boon, noticeably increasing the mage's
flexibility, and thus their power. Another advantage is that, since a
mage does not need to consult their spell book to memorize spells, it
can be safely left at home, rather than being risked to the vagaries of
weather, river crossings, thieves, and fireballs on long adventures.

Why is this possible? To my knowledge, little research has been done
on the subject, but presumably on such planes it is sufficiently much
easier to assemble the structure of a spell and make the contacts to
other planes necessary to power it, that the specific spell need not be
memorised in advance, and merely the words, gestures and substances
normally used to trigger the stored spell are sufficient to create it as
 well. The mana necessary to establish a mana flow from other planes to
power the spell evidently comes from the mage (thus the maximum number
of spells per day). Recovering this mana happens during
sleep/rest/meditation on most planes. On some others, as well as
sufficient sleep, some form of meditation or study is necessary,
sometimes with the mage's spell book, for the same period as would be
required to memorise the spell: on such planes evidently the mana to
cast the spell must be laboriously assembled and stored, but the
structure of the specific spell to be cast does not. On some planes the
mana recovers slowly over a 24 hour period, partially (as is the case
for psionics) or completely independent of the mage's other activities. I
 have even heard of planes where the mana recovery happens at some
specific time, such a dawn or midnight, though this is much more common
for clerics (where it is evidently a book-keeping convenience imposed by
 the cleric's deity, as it often differs between religions).

• Spell casting cannot be done while prone or crouching if there is a somatic component.
• Spell casting negates dexterity bonuses to AC during the time of
casting. During the earlier and later segments of casting dexterity
applies.
• No spell may be cast if the spell description is not in front of the
player, and the caster states his intention and target at the beginning
of the round.
• Spells do no more than what is listed, and where there is room for
interpretation, the DM, not the player, determines the interpretation.
• Also note that characters who are spellcasting lose all dexterity
bonuses while they are doing so (this is not an addition to the official
 rules, but a reminder of them).