How to implement divine spellcasting mechanically, i.e. what should it look like?

[Greywander]

There's a few different ideas for magic systems that I've been playing with that I'd like to implement alongside each other in order to give players different options for playing magical characters. I want each system to feel different and unique, and to appeal to different types of players and styles of play. At the moment, I'm leaning toward using Fudge as the basis on which to build an original system that includes these magic systems, but I'm not sure how relevant that will be.

The thing is, I'm not really sure what I should do mechanically for theurgy (aka Divine magic). I at least have a solid idea for what each of the other magic systems looks like, if not the exact implementation. It would probably be helpful for me to go over these other magic systems first so that you can sort of see what I'm going for as a whole as well as which mechanics already exist so that theurgy can be different from those.

Sorcery is basically your superhero magic. Many creatures have their own innate supernatural traits and abilities, and those traits and abilities sometimes manifest in humans as sorcery. Each sorcerer has one (or more) bloodline that determines which sorceries they'll have access to, as well as what sort of weakness they have. For example, a sorcerer with a fey bloodline will have access to things like shapeshifting and illusions, and will find their sorceries foiled by iron (e.g. offensive sorceries can't penetrate iron armor, or slap a pair of iron handcuffs on 'em and they can't use any fey sorcery).

Sorceries will probably be either at-will or running on some kind of stamina mechanic. In any case, they're mostly spammable and viable for combat use. This makes sorcery quite powerful, but the tradeoff will likely be a high XP cost to level up multiple sorceries. Because of this, many sorcerers will probably just pick up a few build-defining sorceries and use them to enhance otherwise mundane abilities. The end result will likely look a lot like a comic book superhero. "Full caster" sorcerers can be quite powerful, but also cost a lot of XP to build.

Geomagy is a ritual-based spellcasting system; basically magical programming via arcane symbols and geometric figures. Something like the alchemy of FMA. A geomagus is basically a wizard, but because their magic is all rituals they have limited combat application. They can draw a spell on a scroll and carry it with them (and scrolls are not generally consumed), but we're probably talking something that is 3 or 6 feet in diameter, and the general rule is that the magic only affects things inside the magic circle. The size of the spell will affect its power, as well as needing to fit the spell's target entirely within the geometric figure, which is why you might need it to be that big. Some or all spells will also have spots drawn in to the figure where you need to place the material components, which may or may not be consumed. Otherwise, once a spell is drawn, it is permanently active until either part of it is erased or one of the components runs out.

I'm debating between making each individual spell a trait you have to spend XP for, and making a skill that lets you "freestyle" spells. I could do both; knowing a specific spell lets you draw it without needing to roll, and gives a bonus if you tweak that spell, whereas trying to freestyle has a risk of the spell simply not working or having an unintended effect. I'm still figuring out how dangerous this should be; I imagine that a fair number of mages simply disappear one day, the result of drawing a spell incorrectly with a catastrophic outcome, but I think I'd rather steer clear world-ending bugs in a spell's code. The universe must have pretty good error handling, otherwise an errant mage would have accidentally destroyed it by now from a typo in one of their spells.

Witchcraft is where you make contracts with spirits and other creatures to perform a service in exchange for payment. Any spirit you've contracted is called a familiar. Usually you're either finding spirits in the wild or learning a ritual that allows you to summon or contact that spirit (this might overlap with geomagy, though these rituals might also be something else entirely). Usually these contracts take the form of permanent minions, temporary summons, spellcasting-by-proxy (where you call up a familiar to use one of its abilities on your behalf), or buffing via possession (the spirit possesses you in order to extend some of its traits to you, e.g. a troll giving you regeneration; naturally there's some danger to this).

A big part of witchcraft is negotiating with the spirit and writing up a contract. What I have in mind is for a contract to read more like a D&D class feature and less like an actual legal document, so my plan is to basically create an outline of the different sections for a contract, each of which should only be one or two paragraphs. The most important parts would be Services (what the familiar is expected to do for you) and Payment (what you are expected to provide to the familiar), but other sections would deal with things such as the conditions under which the contract can be terminated, if you or your familiar can be compelled to provide services or payment against your will, and what the consequences are for violating the contract (e.g. failing to provide services or payment).

So now we come to Theurgy. Fundamentally, theurgy is the same type of magic as witchcraft, the major difference is the power of the spirits involved (gods vs. anything else) and your relationship with that spirit (ruler/subject vs. business transaction). Practically, the two are very different, mostly because the gods are so much stronger than any other spirit out there.

Each god will probably have their own system for determining who gets to be a theurge. I can broadly see splitting it into two categories: clerics, and prophets. Clerics are basically "super priests"; they are part of the priesthood and trained well beyond what most priests are, then undergo a ritual to see if their god chooses to extend their power to them. Those who are rejected return to the priesthood, but those who are chosen become full clerics, vessels of their god's divine will. Prophets, on the other hand, can be literally anyone, even someone who doesn't worship that god, and the god just decided to grant them power just because. Usually this is because the god in question tends to be the Chessmaster, and this particular person having divine power is all part of The Plan™. Clerics are generally expected to adhere to a set of tenets and to actively further their god's agenda, whereas prophets can do as they please but have no guaranty their power won't be taken away as suddenly as it was given. Mostly, this is just a difference in RP.

What I don't have figured out is the actual mechanical implementation of theurgy. What exactly are you spending XP on? How do you cast your spells? Does it expend a resource? Is there some randomness depending on how your god is feeling? How does theurgy fit in with, and differ from, the other magic systems described above? How can I use the mechanics to evoke the feeling of being a vessel of divine will?

That's kind of where I'm at. Anyway, I realize I rambled on a bit there, so thanks for taking the time to read through this.

[MrStabby]

I would look at components.

Divine magic is about prayer. Loud prayer Devoted, top of one's voice attention grabbing, shouting to high heavens type prayer. Not subtle.


Witchcraft is more subtle. A token of a bargain struck here and there. A mark made on the skin as a reminder of a debt owed. Whispered exchanges in the dark.

So one has more of a leaning towards verbal components, one towards material (or I guess spiritual if souls can be a medium of exchange with the appropriate entities?)

[LibraryOgre]

What I'd be inclined for with Priestly Magic would be that it has two aspects... Geomagy-like ceremonies that require special settings and equipment (basically, prayers that require a church, vestments, the whole nine yards, that affect entire groups of parishioners, but not many people outside the walls of their church), and "tokens"... basically, very specific spells that do very specific things, and can only be used for a limited time, or a limited number of times.

So, your priest might be able to Bless an entire congregation, or have a funeral that protected the corpse from rising as undead, but their "in the moment" spells would be limited to "You can cast Heal Wounds three times within the next ten days."

[Grod_The_Giant]

From your descriptions, it sounds like clerics would basically use Geomancy, focused on broad, subtle blessings and divinations.

Prophets sound a lot more like Sorcery, but I could also see a more ad-hoc sort of system. Instead of knowing a set of formal spells, they just say "yo, god, give me a hand" and a miracle happens. Something big, flashy, and not really under their control.

[Baniff]

Each deity has a list of spells. Once you cast a spell, you have to do a specific task to "recharge" it.

You cast Heal, and now you must fast for a day before you can cast it again.

[MrStabby]

Each deity has a list of spells. Once you cast a spell, you have to do a specific task to "recharge" it.

You cast Heal, and now you must fast for a day before you can cast it again.

Huh. A quest based magic system sounds pretty cool. I might have to steal that idea.

[Greywander]

Each deity has a list of spells. Once you cast a spell, you have to do a specific task to "recharge" it.

You cast Heal, and now you must fast for a day before you can cast it again.
I almost remember proposing a similar magic system some time ago, where you would need to do a special ritual for each spell, but after casting it. This post jogged my memory, though I still don't remember the details, if indeed I did suggest something similar.

Perhaps the best implementation of something like this is with some kind of magic point system (you could call it something else, like "faith" or "favor"). Casting the spell consumes the resource, performing the ritual (which is specific to the spell cast) restores the resource, or the resource will also restore gradually over time, e.g. after a long rest or equivalent. Spell slots would also work. You could also make each spell usable exactly once before needing to do the ritual for that spell. Seems like there's a few different ways of implementing this. And of course if you have the time you can always perform the ritual at the same time as casting, instead of doing it later.

Seems like it strikes an interesting middle ground between a pure ritual casting and pure spamming. Spam now, ritual later to recharge.

[Baniff]

After more thinking, I've come to the conclusion that Pact magic and Divine have one important difference- with a pact, you know the exact terms. You do this and you get that. A diety should feel unknowable and only semi-predictable.
Maybe your spell list is random each day? It's hard to make a class that's fun and subservient. I've never had a player actually sacrifice anything to be a cleric or paladin :p

[Herbert_W]

This is a question that has two parts - what features theurgy might be expected to have and how to mechanically represent those features - and I think it's best to approach those parts in that order.

Here’s a quick list of features that I'd consider a natural fit for theurgy:


Rituals: The most common form of spellcasting that I’d expect to see for a theurgist (though not the most interesting for player characters) is rituals. Rituals are commonly used and, as a general rule with few exceptions, don't produce dramatic results. Many faiths hold certain rituals regularly at given times of year - a ritual to give thanks for the harvest art harvest time, a ritual to pray for protection as winter sets in, and a ritual to pray for a good yield when planting crops, etc. Almost anyone can learn rituals, barring only those who the God being petitioned actively dislikes. Every member of the priesthood should have at least some proficiency with rituals, although some prophets might not.
Prayers: This is what makes theurgists as-in the adventuring class special and distinct from the rest of the priesthood - they are blessed with the ability to call down the power of their God. Prayers are fast, more flexible than rituals, and can produce immediate and dramatic effects.
Domains: I like the 3e domain system but I don’t think that it goes quite far enough. I’d give every theurgist a short list of prayer effects that they can produce by default, and have most of their prayer list come from domains which they can invest build resources into advancing. Low-level theurgists can only have domains granted by their patron deity, but higher-level theurgists can learn domains from allied deities, and extremely accomplished theurgists can learn domains from any non-opposed deity.
Resource management: Channeling the power of a God is hard on both body and soul. I’d expect using theurgy to consume some abstract resource that represents this and which recharges on a long rest.
Running on empty: Divine casters should always be able to try to produce a prayer effect, although not with the power or reliability of a theurgist who is well-rested and prepared. Other casters might know in advance exactly how many times they can cast fireball and then exactly what they need to do before they can cast it again, but theurgists are different. Theurgists call upon he power of Gods, and that power is inexhaustible (at least, by non-epic mortal spellcasting).
Variable results: A failed fireball might fizzle, but a miscast heal should still do something, even if it only stabilizes the intended beneficiary instead of sending them back into the fight.
Healing and hordebusting: Theurgists are obviously inspired by clerics, and clerics are classically construed as capable party healers and anti-undead specialists. I don’t expect every theurgist to specilize in these roles, but I do expect the majority of theurgists to be at least competent at both. I’d expect the default list of theurgist prayer effects to include both healing and warding against the undead.
No item dependency: While a theurgist might benefit from owning a relic or specially blessed holy symbol, I’d expect a theurgist to be an at least competent contributor to the party even when equipped with only their faith. This means both that items shouldn’t be necessary for using any of a theurgist’s abilities and that items shouldn’t be so beneficial that the disparity in power between an equipped and unequipped theurgist is enough to throw off the game’s balance.


In order to implement these features, I’d make the use of theurgy require a skill check, with the DC determined by the magnitude of the expected effect and bonus depending on investment in either general theurgy or the relevant domain. A failed check doesn’t automatically mean that the prayer effect fails - it means that spellcasting juice is expended. If the player is out of juice, a lower-level effect is produced as appropriate for the player's skill check result. Prayers should only outright fail when the check fails, the player doesn't have enough juice, and there is no appropriate lower-level effect to be produced. I’d balance the DC in such a way that theurgists can automatically succeed on checks for minor effects (the equivalent of 5e’s cantrips) but will basically never be able to automatically succeed on checks for major effects (and thus can’t spam them).

This spellcasting resource could be the same one that other spellcasting classes use. I like the way that 5e handles spell slots for multiclass characters (i.e. the same way that 3e handles BAB) and something similar could be good here.