Can the Detect Magic spell detect prepared spells or spellcasters?

Question

Inspired by a recent question about discerning divine and arcane spellcasters, of like to hear the case for and against detecting spellcasters of either style with detect magic.

I think you can detect whether someone has prepared spells, based on this language:

For the duration, you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any. (emphasis mine)

Preparing spells is described as having the spell "fixed in mind" (p. 78 Player Basic D&D v0.2). I'd argue that qualifies as bearing magic, and opens the door to using detect magic to identify spellcasters with currently prepared spells. What do you think?

Answer 1

No, detect magic doesn't automatically detect spellcasters as magical

The Sage Advice Compendium addresses a related question:

Is the breath weapon of a dragon magical?

If you cast antimagic field, don armor of invulnerability, or use another feature of the game that protects against magical or non-magical effects, you might ask yourself, “Will this protect me against a dragon’s breath?” The breath weapon of a typical dragon isn’t considered magical, so antimagic field won’t help you but armor of invulnerability will.

You might be thinking, “Dragons seem pretty magical to me.” And yes, they are extraordinary! Their description even says they’re magical. But our game makes a distinction between two types of magic:

• the background magic that is part of the D&D multiverse’s physics and the physiology of many D&D creatures
• the concentrated magical energy that is contained in a magic item or channeled to create a spell or other focused magical effect

In D&D, the first type of magic is part of nature. It is no more dispellable than the wind. A monster like a dragon exists because of that magic-enhanced nature. The second type of magic is what the rules are concerned about. When a rule refers to something being magical, it’s referring to that second type. Determining whether a game feature is magical is straightforward. Ask yourself these questions about the feature:

• Is it a magic item?
• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?
• Is it a spell attack?
• Is it fueled by the use of spell slots?
• Does its description say it’s magical?

If your answer to any of those questions is yes, the feature is magical.

Let’s look at a white dragon’s Cold Breath and ask ourselves those questions. First, Cold Breath isn’t a magic item. Second, its description mentions no spell. Third, it’s not a spell attack. Fourth, the word “magical” appears nowhere in its description. Our conclusion: Cold Breath is not considered a magical game effect, even though we know that dragons are amazing, supernatural beings.

Detect magic, like other game mechanics, operates by this same logic with regard to what is considered magical. The spellcasting abilities of creatures (innate or otherwise) are considered "the background magic that is part of [...] the physiology of many D&D creatures". Detect magic is designed to detect magical effects, not the background magic that suffuses creatures or the universe.

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Chris Perkins confirms this sort of interpretation here:

Can detect magic detect magic potential of spellcasters even if they're not actively casting a spell?

It's not a wizard detector, if that's what you mean.

Given that the question he's responding to asks about spellcasters in general, it seems clear that his response is not specific to wizards - he's suggesting that the spell doesn't automatically detect spellcasters simply due to their magical abilities.

Answer 2

There is no game-mechanic definition of "bears" as the word is used in the spell description. It is going to be up to you and your group how to interpret the spell wording, and loose wording of spell descriptions does seem to be a common device in 5E - I suspect it is deliberate policy to support "play as you like".

This does open the door to allowing many creative uses of spells, possibly not foreseen by the game developers, and very likely taking different interpretations at different tables.

Personally I don't buy your argument for prepared spells counting as "bearing magic", I think it stretches the language and intended use too much. I would restrict detection to spells and items after they have been created, and not include the latent magical ability within a creature before it has been manifested.

Like a house-rule, it helps to think through consequences of applying your reading of the rules consistently. To be clear, I am not saying this is a house rule, it is an interpretation, and I do not believe there is a strict reading of RAW that says "no".

For your suggested use of the Detect Magic spell I can think of the following:

• It somewhat boosts the utility of Detect Magic. For campaigns with otherwise low amounts of magical items and effects, where the spell might be dropped for lack of use, this could be welcome.

• It might be a relatively cheap and easy way to resolve plots involving mysteries. This is always a danger with divination spells - there is a tension between making them useful versus allowing them to solve a whole plot through creative thinking. So if you allow Detect Magic to detect spellcasters, make sure that knowing who is or isn't a spell caster (especially secretly a spellcaster) is not a plot spoiler. Or at least make it a difficult task to find and confront the suspect before using Detect Magic to reveal, that yes not only did he have motive, but also knows the Necromantic magic that caused the victim's death.

Neither of these are a game-breaker in my opinion, so I think the door is still open. However, I advise discussion before this one is used. A good rule of thumb is that you don't want to be having a rules debate at the same time as when the outcome of the rule decides the fate of a player character. And this interpretation is debatable enough that you could lose game time to it.

Answer 3

I would interpret "bears magic" in this sense, to mean, "has active magical effects".

So,

• A Wizard who has prepared spells, or a Sorcerer who has innate magical power, would not be detected.
• A character who was under the effect of a spell (even one with no visible effect, eg Comprehend Languages), would be detected.
• Magic items are under the effect of (usually permanent) spells, so would be detected.