This issue is already covered in the skill description.



You can share a Tradition (the knowledge) without sharing a Source (ability to cast spells) to learn . Access to a Source is severely restricted, due to jealousy amongst the gods.

Requiring the ability to also cast spells of that Source prevents Martials and (non-casting) Experts from having a reason to broaden their skills.
Attacking a heavily armoured foe with a dagger is a good time to instead provide assists (melee or Ritual Casting).

That's what I get for not going back and reading the entries. Given that, I don't think changes are really necessary. What's seems to be required is the correct Arcanum skill (no casting ability required).

The way the word "Tradition" is used in the Arcanum skill description is quite clearly not the same meaning of the word Tradition in the other magic rules of the book, but the skill description uses the word "Tradition" to convey what other parts of the rules mean by "Source." Compare ARPG pages 141 with 322-42.

It is not clear based on the wording of the skill use whether it intends to allow those without the ability to cast spells to be able to assist in casting spells. I can see it argued either way, though I personally feel that only spell casters should be able to assist in casting. A definitive answer would be appreciated.

I agree that the Arcanum skill entry uses Tradition where the rest of the rulebook uses Source. However, beyond that, I think it is clear what the rules say because the Arcanum skill writeup is consistent within itself - you merely need to have at least 1 rank in the matching Arcanum skill in order to assist in casting (you don't need to be a caster yourself).

Below is an alternative interpretation and clarification of the ritualistic casting rule. The one I posted previously is my own preferred interpretation of the rule, but this is how I think some others are suggesting it be interpreted (and made explicit on the vague parts to dot i's and cross t's).

Ritualistic Casting
Assist, Special: Characters who share understanding of an Arcanum Source may assist each other on Arcanum Skill Actions in a ritualistic form of spell casting. The +2 bonus from assistance applies to any Skill Roll to successfully cast the spell as well as any Skill Roll to resolve the spell's effects. Sustained spells receive the bonus only for the initial effects unless the assistant continues to assist, in which case the assistance bonus applies as long as the assistance persists at a sustenance tick.
The assisting character must have at least one rank in the same Arcanum sub-skill that the primary caster is using to invoke the spell. The assisting character does not need to have any spell casting ability himself.
This ritualistic skill assistance is similar to assisting on any other skill roll (see Cooperation, p.136) but may also be used in combat. When used in combat, the assistant(s) must start their assist action at the same tick or 1 tick before the primary spell caster begins casting the spell. The character who is providing the assist must perform a Demanding (7 ticks) Skill Action to assist. If the assistant takes any damage while assisting before the spell has been successfully cast, the attempt to assist automatically fails.

[Wearing my GM hat and trying to thwart players who want to misread rules. It's a wordy description, but I've read too many discussion boards wherein RPG players disagree about rule intentions when things aren't explicit.]

I'm not sure if I personally prefer the assistant to have spell casting of the source or not. However, I think the rules say you don't need to have spell casting.

One thing I'm curious on is where did the auto-fail if you take damage come from? I don't remember seeing it under ritualistic casting or elsewhere. I would have expected it to work the same as casting an interruptible spell (you have to make a roll to continue the action).

This is specific to Arcanum: Ritualistic Casting, pg.141


You don't get to make the Mettle roll that any other Interruptible action can try. (pg.303)

Ah. Yep. I missed the last line. Odd that only ritualistic casting of all the interruptable actions does not get a roll to continue.

On further thought, if the assistant needs only ranks and does not need to be able to cast spells, then it can violate the spirit of Henry's firm rule of no mixing of divine and arcane magic in a single character. In Arcanis, it's an inviolate rule that no person can cast both cants and arcane (primal, elder, or eldritch) magic spells. Assisting in a ritual is not casting a spell per se, but it feels like it goes against the spirit of the rule.

With the second rule proposal and interpretation of the ARPG rule that only skill training is required, a divine caster could assist with casting an eldritch spell or vice versa. On the other hand, if it is required that the assistant has the ability to cast spells himself, there is no issue with helping someone cast a different type of spell.