Is there a serious balance problem allowing all casters to use Arcana with their casting stat?

Question

I'm considering a house rule in a campaign I'm about to DM for that allows those with the spellcasting, pact magic or similar abilities to use their casting stat as the associated stat for the arcana skill. For example, a Druid would have Arcana(Wisdom) instead of Arcana(Intelligence). This would represent each character funneling their knowledge of magic through their particular way of interacting with magic.

My thought is that this would devalue wizards somewhat, as previously they were pretty much the only ones with a good stat synergy for the arcana skill, and in general make Intelligence a less valuable stat.

The level of balance I'm concerned about is if someone who was considering choosing to play a wizard (or other INT based class) would likely switch to a different class to take advantage of the rule. Less than that and I'm not that concerned about the details, but I'd like to hear any impacts that I haven't though of.

Answer 1

Probably not

Skills are not hard-coded to any ability (see the "Using Ability Scores" portion of the basic rules). The ability that appears beside them and in their descriptions is only the most common. For example: Intimidation is most often used with Charisma. But given certain situations, like a strongman crushing a rock with his bare hands to intimidate, that would make sense as an Intimidation (Strength) check, or in a trial a smart character could try to intimidate a member of the jury slipping certain details in his speech that let him know that you are unto him, that would probably be an Intimidate (Intelligence) check.

In total, if you allow Arcana (Wisdom) or Arcana (Charisma) checks the variance would be of just two or three points in a d20 roll. It would be noticed, yes, but nothing too wild.

However

Your solution might not be needed.

Not all magical knowledge falls under the Arcana skill. You can use Religion for divine spells from Clerics or Paladins, and Nature for spells from Druids and Rangers. And since you can attribute any Ability to any Skill as long as it fits, all of those could use Religion (Wisdom) or Nature (Wisdom) for their spell know-how, arguing that they operate their spells more from "instinct" than "intelligence".

This means that to know what a Druid is casting, your Wizard might need to do probably a Nature (Intelligence) check, as he does operate via intelligence, but the knowledge he is trying to figure out is not Arcane at all, but natural. But this is not RAW nor RAI so take it just as a flavorful suggestion.

This has another reason to be, and that's balance. Other than your magical know-how, every knowledge skill has different areas of expertise.

Arcana. Your Intelligence (Arcana) check measures your ability to recall lore about Spells, Magic Items, eldritch symbols, magical traditions, The Planes of Existence, and the inhabitants of those planes.

Nature. Your Intelligence (Nature) check measures your ability to recall lore about terrain, Plants and animals, the weather, and natural cycles.

Religion. Your Intelligence (Religion) check measures your ability to recall lore about deities, rites and prayers, religious hierarchies, holy symbols, and the practices of secret cults.

Note that every single one of these let's you know completely different things. Like with Nature you would be able to know details about any beast or plant-like monster, or with Religion you would be able to know details about Fiends and Celestials and other godly/ungodly servants, or Arcana would let you know how to get to the Fire Plane or weaknesses of a Shadowfell monster.

If you encourage your players to spread their knowledge abilities they gain a lot of coverage, instead of concentrating everything on Arcana.

Answer 2

Not really.

Arcana isn't useful in combat so giving someone a slight boost to Arcana doesn't really break anything major. It doesn't extend the range of possible Arcana checks beyond anything a party couldn't normally do, and it's useful if your party chooses not to have a wizard, but the DM hopes they're going to pass Arcana checks to find interesting information.

A problem is if you have a wizard in the party who has high Arcana, and someone else beats them at their specialty. Or, if players feel that wizards should really be the ones good at Arcana, or feel that a cleric or druid knowing Arcana and using Wisdom doesn't feel right or make sense. That can be discongruous or feel implausible to the party, and you may want to avoid it for those reasons, but it's not particularly overpowered and won't seriously unbalance the game.

The introduction to Chapter 9 of the Dungeon Master's Guide (p. 263) gives this guidance on house rules:

Before you add a new rule to your campaign, ask yourself two questions:

• Will the rule improve the game?
• Will my players like it?

If you're confident that the answer to both questions is yes, then you have nothing to lose by giving it a try. Urge your players to provide feedback.

The Player's Handbook (p. 175) and the Basic Rules do suggest that skill checks can be made with alternate abilities, at least sometimes, under "Variant: Skills with Different Abilities":

In some cases, though, your proficiency might reasonably apply to a different kind of check. In such cases, the DM might ask for a check using an unusual combination of ability and skill, or you might ask your DM if you can apply a proficiency to a different check.

If you've got a good reason why, say, a sorcerer can draw arcane knowledge from Charisma, it's a legitimate variant within the rules to allow it.

Answer 3

RPG.SE user @Helwar made this comment (and has now made a full answer), which I thought would make for an interesting answer, so I decided to make this answer based on that comment.

I can't say if it's unbalanced or not. In theory it doesn't look that bad, it's just 2 or 3 points variance in a d20... But I just wanted to be sure you know that a Cleric / Paladin "magic knowledge" is measured through "Religion", and divine/fiendish creatures knowledge is acquired through Religion (most often), and that a Druid / Ranger "magic knowledge" comes from Nature. Arcana does not contain all magic knowledge, just the arcane one. This rule of yours would help Warlocks, Bards, Sorcerers and 1/3 arcane casters, but would do nothing for divines. Just so you know

So, to reiterate the points of interest from my perspective:

• The Arcana skill is about "arcane" magic specifically; a Wizard's expertise in this reflects their academic understanding of their arcane magic; see kviiri's answer or Helwar's answer for the Arcana skill description quote.
• Clerics and Paladins can already express knowledge about magic via the Religion skill, since that's how they understand their magic. They wouldn't have any reason to understand "arcane" magic any better (i.e. via Wisdom, or Charisma for Paladins) because they're "divine" casters.
• Similarly, Druids and Rangers can already express knowledge about magic via the Nature skill, since again that's how they understand their magic. They also wouldn't have any reason to understand "arcane" magic any better (i.e. via Wisdom) because they're "divine" casters as well.

It's only really Bards, Sorcerers and Warlocks that are left out here, being Arcane casters that don't really need high Intelligence.

Therefore, I'd say it would make thematic sense to allow those classes specifically to make Arcana (Charisma) checks specifically to reflect the fact that their knowledge of arcane magic comes from how they channel it with their will (or whatever) as opposed to study (i.e. Intelligence, as a Wizard).

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I'd say Arcana (Wisdom) makes no sense for divine casters because they don't understand magic as intuitively in terms of the arcane, so applying Wisdom to the Arcana skill makes no sense, and they don't need it anyway (as they have Religion and Nature).

There is a case for them making Religion (Wisdom) and Nature (Wisdom) checks (or Religion (Charisma) for Paladins) as opposed to Religion (Intelligence) or Nature (Intelligence) checks if the check is being made about magic, since they understand their magic in terms of Wisdom/Charisma, rather than academic study like Wizards, although this wouldn't apply to things like knowledge of fiends, because a Paladin (for example) would know about that through study, not through magic, so Religion (Intelligence) would still be more relevant for that context.

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Regarding balance, however, as others have said, it's just a skill check that has a minor influence on its d20 roll, so changing this wouldn't affect very much at all except possibly your player's class choices, but even then that's only if their character concept revolved heavily around the Arcana skill specifically, which I doubt this "houserule" (and as Quadratic Wizard's answer points out, this does have RAW support in the PHB pg. 175, so it's not really a houserule) would upset to the point that they'd change their entire character concept over one skill check.

Answer 4

It depends - probably not

DnD 5e leaves the utility of skill rolls largely in the GM's hands. Therefore, how much difference Arcana makes depends a lot on the type of campaign you have. I have played a campaign of DnD 5e where I don't recall anyone rolling Arcana ever, at all.

The skill is described as follows:

Your Intelligence (Arcana) check measures your ability to recall lor about spells, magic items, eldritch symbols, magical traditions, the planes of existence, and the inhabitants of those planes.

If any of those are very important in your game, Arcana is valuable. An example is that if you frequently run enemies with unusual weaknesses that can be learned through successful Arcana checks, that makes the skill very valuable, but still not likely to be a serious balance problem as skill proficiencies are a fairly small part of any character's total power. Otherwise, it's likely to be a rather insignificant change.