Is a soul or spirit a creature?

Question

The new Unearthed Arcana gives a new option for warlock's patron: The Undead. One of its class feature is Spirit Projection:

Your body is now simply a vessel for your spirit. As an action, you can project your spirit from your body. The body you leave behind is unconscious and in a state of suspended animation.

This is just an example of effects that cause spirit or soul leaving their body. There are other similar effects like, although different, astral projection and magic jar spell.

When out of their body, does a soul or spirit count as (normal) creature? Can they be targeted by effects? Can they be seen? What happens when either the body or spirit/soul targeted by an effect? Do both got affected?

Answer 1

D&D 5e has some core rules-under-the-rules. The first is: The rules do what they say they do.

Given that, let's look at the rules text of this specific power.

While projecting your spirit, you gain the following benefits:

• Your spirit and body gain resistance to bludgeoning, piercing, and slashing damage.

• When you cast a spell of the conjuration or necromancy school, the spell doesn’t require verbal, somatic, or material components that lack a gold cost.

• You have a flying speed equal to your walking speed and can hover. You can move through creatures and objects as if they were difficult terrain, but you take 1d10 force damage if you end your turn inside a creature or an object.

• While you are using your Form of Dread, once during each of your turns when you deal necrotic damage to a creature, you regain hit points equal to half the amount of necrotic damage dealt.

So what does this tell us? Well, both the body and the spirit are subject to damage, as both receive damage resistance. By inference, both can be effectively targeted. Nothing is said about funny things happening with HP, so presumably it's all coming out of the same HP pool. Nothing is said about effects, so, by default, anything that hit either the person or the spirit would affect the whole. So... basically, they're both a creature, but they're both the same creature, who now happens to have two locations they can be targeted from. They can fly and pass through items (because it says they can) but they're not invisible (because it would have said they were if they were, and it didn't.)

Some of that is starting to wander towards the realm of "reasonable supposition", though. After all, another one of the underlying principles is Rule 0: The rules do what the DM says they do.

Unlike many other tabletop games, 5e actually leaves a lot of the funny little edge cases undefined, and subject to DM interpretation. The core of the game is balanced enough that most forms of reasonable DM adjudication won't break things one way or the other. That's pretty clearly what's going on in this case. Some of the potential interactions are left unspecified, even when some sort of an effect might be reasonably expected. (Does your astrally projected self keep the AC for your armor? Can he stab people?). It's up to the DM to make the call.

The final bit that's pertinent here is Unearthed Arcana Rules are for Playtest. On top of 5e's general inclination towards looseness at the edges and DM adjudication, the stuff that comes out of UA is not yet deeply analyzed or fully playtested. Testing this stuff out and figuring out the issues is what UA is for. Thus, it's often going to leave some of the implications undefined, and it's going to require even more DM adjudication than normal.

...and that finally rolls around to a bit of a frame challenge... because there isn't a grand unified "how do souls work" in 5e, unless your DM comes up with one. Effects that muck with the soul are few enough and far enough between that they'll each have their own specialist rules, which may or may not be entirely in alignment, but almost certainly won't clearly define everything. Basically, for any one spell or effect, if you want to know how it treats souls, then you need to read it (and read the entire thing - there is no crunch/fluff divide anymore) and if it's still not clear, you need to get your DM to adjudicate (or, if you're the DM, you need to make the call yourself).

Answer 2

Not under most circumstances

The rules make no explict statements about what souls and spirits are, but from interactions with other game elements we can conclude that in their normal state, souls or spirits are not creatures. They can take the form of a creature under special circumstances.

Definitions

First, what is a creature? The term is not explictily defined, so anything you commonly would call a creature which according to the dictionary is a living thing that can move independently, and from the rules player characters and monsters are creatures.

Second, are soul and spirit the same thing? For the most part, the terms soul and spirit seem to be used interchangeably, soul is used more in the context of player characters and raising the dead, while spirit is used more commonly for nature and summoning. The speak with dead spell says

This spell doesn't return the creature's soul to its body, only its animating spirit.

so in this instance there is a difference between soul and spirit, but it seems that the term "animating spirit" means something different than spirit in general and is used more to convey limitations of the spell. So for this answer, we will consider soul and spirit as two different words for the same thing.

Manifested souls

Souls or spirits certainly can be creatures. The Ghost, a medium undead creature has this lore:

A ghost is the soul of a once-living creature, bound to haunt a specific location, creature, or object

So she clearly is a soul and a creature at the same time. The Specter, another medium undead creature, has this lore:

A specter is the angry, unfettered spirit of a humanoid that has been prevented from passing to the afterlife.

Again, the specter is a spirit and also a creature. Likewise, multiple spells can summon spirits that take the form of creatures, for example Conjure Animals, Conjure Fey, Find Familiar, Find Steed. These spells typically have language similar to this from Conjure Animals

You summon fey spirits that take the form of beasts

Beasts, fey, etc. are all creatures, so all of these spells summon spirits that also are creatures.

You might call these creatures "manifested" souls or spirits, because they have taken form as a creature. In all of these cases, there is a special cause that made the soul or spirit take the form of a creature. What about the nature of the spirits before they took this form?

Un-manifested souls

Souls like creaturs do have a defined location, typically because they are part of a creature, or entrapped in an object, or upon death (DMG p. 24):

When a creature dies, its soul departs its body, leaves the Material Plane, travels through the Astral Plane, and goes to abide on the plane where the creature's deity resides.

What about the other attributes required for creatures, like hp, and AC?

Spirit Guardians summons spirits, exhibiting angelic, fey or fiendish forms.

You call forth spirits to protect you. They flit around you

These spirits are clearly no creatures, having no AC, hp or way to even be attacked. This proves that generally spirits are not creatures, even when they do take visible form.

All instances of spells that talk about transferring souls (e.g. Magic Jar, Raise Dead, Reincarnation, Ressurection etc.), provide no game statistics for the soul, as would needed if the soul were a creature. Most of these spells also would not make sense, as a creature cannot "have" another creature.

From all of this evidence, we can conclude that in their default state, souls or spirits are not creatures under the game rules.

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P.S. A special case is when a ghost takes Possession of another creature, the ghost then disappears but it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics. The two creatures (ghost and target) are somehow merged into one here, but in this case the manifested soul that is the ghost was a creature already to begin with.