The 8th level MU spell binding found in Unearthed Arcana describes the ability of up to six assistant mages to essentially enhance the power of the primary spell caster.
Can anyone explain to me, in 1st Edition rules, how this could not be applied to all MU spells (or Cleric spells too, for that matter)?
Well, it's 1st edition rules. The simplest explanation is "because it isn't in the rules".
AD&D's magic system isn't very clearly defined, with the abstraction of spell slots being hard to apply to in-game magical metaphysics. That's why we get questions like this, and that's why we got the very awkward mechanics of metamagic feats in later editions, just to make this unwieldy mess a bit more flexible.
Specific settings would sometimes make magic a bit more coherent with regard to in-setting metaphysics (Dark Sun, for instance), but even then, a lot is just accepted as is.
AD&D1e had no mechanics for any kind of combined or ceremonial casting, except for some vague notes about combining castings of Dispel Magic. By the standards of interpretation of the time, these mechanics in Binding would be considered specific to that spell; you might be able to research other spells to work in a similar way, but this would have to be argued on a case-by-case basis.
Unearthed Arcana might not have been considered a strong source of precedent for such an argument. Just about everyone whose reaction to it in the AD&D period I knew (50+, across the UK) looked on it very sceptically. The Chromatic Orb spell made it very clear that one couldn't just accept the spells as a group, and Binding is basically about dealing with demons and devils, which wasn't something that most DMs were keen on their players doing.
From reading the spells it looks to be evocative of various fantasy novels of the day and past that had cabals of sorcerers summoning up a demon. For example the medieval depiction of witches sabbaths. In this case it is written as a specific feature for this spell. Not as a general rule.
As a house rule I used the following for my Majestic Wilderlands campaign. The assumption of my setting is that standard D&D magic is the currently the most advanced form of magic. There are other forms of magic but have disadvantages of one kind or another.
In addition I have a rule that magic-users can cast as a ritual spells from their spell book. The highest level they can cast is 1/2 of the highest level they can memorize rounded down. A magic-user capable of casting 5th level spells can cast upto 2nd level spells as rituals.
The ritual takes 10 minutes to cast, and requires component equal in cost to the spell level squared times 10. A first level spell cost 10 gp to cast, a second 40 gp and so on. The only limit is the fact that it takes a turn (10 minutes) to cast and amount of gp you are willing to spend on components. The turn casting time means that players only use ritual for support spells.
In addition to this I have a class to represent a Order of magic-user known as the Order of Set. The Setites can only cast spells as rituals. However they are can combine their caster levels for a single rituals casting provided they can all cast the ritual in question. So during a siege a 5th level Setitie, 7th level Setite, and a 9th level Setite, can take ten minutes to cast as 21d6 fireball.
What I recommend if you like this idea but not the class, is to allow rituals as above with the limitation of 1/2 the highest level memorizable. And allow casters to combine their levels during the casting of a ritual only.
The advantage of this approach that it will add flavor to AD&D's magic system without requiring a re-writing of the spells. It will allow you to add an additional form of treasure, magical components rated in gp value. It also acts a natural check for the behavior of the characters as the authorities can cut off their ability to buy new components.
The downside of this approach that it will make the casting of utility spells much more common. A prepared group of magic-users can be devastating to their target. In short it will give the campaign a slightly higher feel to it's magic.
I been using this rule for three years now and found it easy to accommodate my adventure preparation to its use.
An argument against "cooperative spell casting" as a general case outside of that very powerful spell (binding) is the Vancian nature of magic-user magic, which uses preparation to implant the magic into the magic-user (loading the brain) before casting the spell. That puts binding -- described as a spell that can draw on multiple casters -- in the category of "exception to the general rule." (The spell description spells out written elements to go with the casting, which points to an intent for this spell to be most frequently cast from a scroll ... but it doesn't make that an explicit limitation).
The components vary according to the form of the dweomer, but include: a continuous chanting utterance read from the scroll or book page giving the spell; (spell description, Binding)
(p.25 PHB )He or she must memorize and prepare for the use of each spell, and its casting makes it necessary to reabsorb the incantation by consulting the proper book of spells before it can again be cast. (See CHARACTER SPELLS for more details). Once cast, a spell is totally forgotten. Gone. The mystical symbols impressed upon the brain carry power, and speaking the spell discharges this power, draining all memory of the spell used. This does not preclude multiple memorization of the same spell, but it does preclude multiple use of a single spell memorized but once. When a spell caster shoots his or her spell-bolt, so to speak, it is gone. (P. 40)
Unless a spell description points to the ability to draw on multiple casters, the spell would be expected to work as above.
or Cleric spells too, for that matter
You can make a decent case for clerical magic, per the points offered below.
When asking the DM to make a change to the magic system, it is helpful to build a case for a ruling favorable to a player's intentions. (Don't dump it all on the DM). Let's work through this case; binding.
It would take divine intervention (DM) for binding to be available to a Cleric. The distinctions between cleric and magic user magic is pretty straightforward, but at the caster level the effect is closely related: you load the spell and then expend it. Both Druid and Cleric spell lists end at 7th level (UA, p. 29, PHB p. 40-41, ), binding is 8th level spell, but, AD&D 1e is flexible.
First, we examine some objections to cleric s gaining this spell, and then some then arguments for. The preface to the DMG(p 6-8) indicates that a DM has broad authority to adapt the game to the campaign. Caveat on page 9:
Know the game systems, and you will know how and when to take upon yourself the ultimate power. To become the final arbiter, rather than the interpreter of the rules ...
While that's explicitly true, it's not as strong of an argument against because a variety of spells are on multiple class spell lists. Examples:
Speak with animals: Cleric level 2, Druid Level 1.
Continual Light: Magic User 2d level, Cleric 3rd level.
Cure Light Wounds: Cleric 1st level, Druid 2d level
Dispel Magic: Magic User 3, Druid 4.
Animate Dead: Cleric 3, Magic User 5
Research. Only magic users are mentioned in spell research/creating new spells.
One can infer that clerics generally can't do spell research due to how they get their spells. (Outside agency aka a deity provides them)
SPELL RESEARCH ... certain that the magic-users in your campaign will eventually get around to inquiring about the procedures necessary to research and create a spell (DMG p.115 - 116)
The differences between clerical magic and magic user/illusionist magic:
(P. 40 PHB) Clerical spells, including the druidic, are bestowed by the gods, so that the cleric need but pray for a few hours and the desired verbal and somatic spell components will be placed properly in his or her mind. First, second, third, and even fourth level spells are granted to the cleric through meditation and devout prayer. This spell giving is accomplished by the lesser servants of the cleric's deity. Fifth, sixth, and seventh level spells can be given to the cleric ONLY by the cleric's deity directly, not through some intermediary source. {snip} Magical spells, those of the magic-user and illusionist, are not bestowed by any supernatural force. Rather, the magic-user (or illusionist) must memorize each spell, verbal and somatic components, and supply himself or herself with any required materials as well. Such memorization requires the character to consult his or her spell books in order to impress the potent, mystical spell formulae upon the mind.
Though an outside agent grants a cleric's spell, the "loaded clip" looks very similar. (The "agency" for a magic user is their own preparation). One can argue that it's the "loaded clip" nature of both types of magic that prevents the cooperative spell method. One can equally argue that having outside agency (deity) involved opens the door for clerical magic to be adaptable to cooperative casting.
Know the game systems, and you will know how and when to take upon yourself the ultimate power. To become the final arbiter, rather than the interpreter of the rules
The DM can change things. To help make the case to your DM, a few supporting points.
At name level (9th level, High Priest) the cleric gets first access to 5th level spells. At High Priest (16th level) a cleric with a wisdom of 18 or greater can cast 7th level spells (if said spells are granted by the deity). (PHB p. 20, cited above)
Is a deity constrained to never grant an 8th level spell? Maybe, if one takes the spell tables as hard coded.
But wait, the level of a given spell can vary with who is casting it!
Speak with animals: Cleric level 2, Druid Level 1.
Continual Light: Magic User 2d level, Cleric 3rd level.
Cure Light Wounds: Cleric 1st level, Druid 2d level
Dispel Magic: Magic User 3, Druid 4
Animate Dead: Cleric 3, Magic User 5
Can a deity grant binding as a 7th level spell? Sure. To help the DM agree that a DM might do this, look at some features of magic as presented.
At 16th level a High Priest is a player character who has had many opportunities to pray for and receive 5-7th level spells from the deity while going from 9th to 16th level. This success likely translates to a deity being reasonably pleased with the Cleric. Since it takes a lot of casters to get this spell to work effectively -- per the spell description -- and there are other requirements (the subject already being bound) this spell being cast cooperatively is a good fit for a temple/shrine/place of worship. A meeting of high level clerics of this deity at a suitable place is a sensible constraint for granting this spell.
A binding spell enables the caster to capture a creature from the lower planes. The subject must already be confined by some form of restraining diagram.
How can the deity help out the cleric and his team of fellow clerics (up to six) in binding this denizen of the lower planes to (choose spell effect).
A scroll
The components vary according to the form of the dweomer, but include: a continuous chanting utterance read from the scroll or book page giving the spell; (spell description, Binding)
Scrolls: (DMG p. 116)
a player character must be at least an 11th level high priest, an archdruid, a 12th level wizard or an 11th level illusionist in order to manufacture magic items (except with respect to potions and scrolls ...)
16th level cleric is high enough level to inscribe a scroll for this providing the deity will bless the cleric with the spell.
Scroll use (DMG p. 118)
The scriber of the spell does not need a read magic spell to use his or her own scroll spells, just as clerics and druids never need the aid of magic to read appropriate scroll spells.
The above is a method generally consistent with how clerical magic works. The cleric, as with any high level spell, communes with/prays directly to the deity asking for this spell (on a scroll?) for the purpose of binding (nastylowerplanedeinzen). The cleric either goes into a trance and writes it down, the scroll descends upon the cleric like 'manna from heaven,' or some other miraculous event (clerics can raise dead, miracles are their business!) enables this scroll to be available. Or a dozen other ways to do this. (Convert a magic user's scroll?)
This boon being granted by the deity is based on:
The cleric's obligation is to convince the deity, or make an appeal to the deity, as played by the DM. Role play opportunity!
For the cleric, as noted above, it never hurts to ask. You may be able to make a better case for other clerical cooperative casting. For a magic user, walk the DM through a similar reasoning to support your case, and be sure to consider constraints and compromises when making the recommendation.
It never hurts to ask.
In my experience, lacking a specific spell for a job either means the system doesn't want you to do it, or that you can research/find a spell to do the job.
Ask your DM if he is willing to allow you to either find a spellbook with the spell you are looking for in it, or maybe buy it off an NPC Magic Guild (if they exist in your campaign), or whether you can research it.
A lot depends on your DM, and whether they think that this spell will either be too powerful or simply not a part of how magic works in your campaign world.
The other thing to consider is spells that have a similar effect in other editions. AD&D 2e is probably the most similar, and it contains a priest spell called 'Combine'. Your DM may allow you to convert it to first edition, and maybe create an equivalent wizard spell. This is quite likely, as a lot of fantasy literature involves ceremonies whereby a single person can use several people's magical power.
In 2nd Edition there was is specific Cleric spell which directly outlines the rules you might be looking for. The spell is called "Combine"
The caster of this spell was usually the most experienced priest, who stood in the center as the assisting priests joined hands to form a ring around the caster. Upon casting the combine spell, his or her effective level was raised by one for each assisting priest. This allowed the caster to turn more powerful undead and cast spells with more range, duration, area of effect, or whatever parameters were related to the caster's experience level. The spells that could be enhanced this way were limited to the spells currently memorized by the caster of combine.
It would be very possible to adapt the rules and mechanics from this spell into a cooperative casting mechanic.
