D&D 5E (2024) Tremorsense and Incorporeal Creatures

[beaumontsebos]

Using common sense... tremorsense would likely not be able to detect an incorporeal creature.

But, is there any actual written rules that preclude this?

Thanks!

 

[Charlaquin]

Using common sense... tremorsense would likely not be able to detect an incorporeal creature.

But, is there any actual written rules that preclude this?

Thanks!

Yes, the rules for Tremorsense. They say, “A creature with Tremorsense can pinpoint the location of creatures and moving objects within a specific range, provided that the creature with Tremorsense and anything it is detecting are both in contact with the same surface (such as the ground, a wall, or a ceiling) or the same liquid.”

An incorporeal creature isn’t in contact with any surface or liquid. You need to be corporal to make contact with other corporal objects and substances.

 

[beaumontsebos]

Yes, the rules for Tremorsense. They say, “A creature with Tremorsense can pinpoint the location of creatures and moving objects within a specific range, provided that the creature with Tremorsense and anything it is detecting are both in contact with the same surface (such as the ground, a wall, or a ceiling) or the same liquid.”

An incorporeal creature isn’t in contact with any surface or liquid. You need to be corporal to make contact with other corporal objects and substances.

Common sense tells you that an incorporeal creature isn't in contact with the surface. But I can't find any rule specifically stating that for an incorporeal creature.

Here's what I've found: Incorporeal Movement. The specter (or whatever creature) can move through other creatures and objects as if they were Difficult Terrain. It takes 5 (1d10) Force damage if it ends its turn inside an object.

If moving through objects is difficult terrain, and they take damage if they end a turn in an object... it kinda means that they are somehow interacting with surfaces in some way.

 

[Stormonu]

Most incorporeal creatures have Flight, so I imagine most of the time they aren't in contact with any surface. However, if the incorporeal creature were to actually be in contact with a surface, I could see it working.

For example, a Xorn touching a wall and realizing it contains a ghost hiding within its bounds, or if a ghost decided to "land" it would be detectable.

 

[beaumontsebos]

Most incorporeal creatures have Flight, so I imagine most of the time they aren't in contact with any surface. However, if the incorporeal creature were to actually be in contact with a surface, I could see it working.

For example, a Xorn touching a wall and realizing it contains a ghost hiding within its bounds, or if a ghost decided to "land" it would be detectable.

That's what I'm thinking. This came up in a game and since there's really not too many times a dwarf can use tremorsense, I allowed it. Just rationalizing my ruling and being sure there isn't an official rule I'm breaking (I'm running a public learning game, so if I use rules different from the official rules, I try to let them know).

 

[Lanefan]

Common sense tells you that an incorporeal creature isn't in contact with the surface. But I can't find any rule specifically stating that for an incorporeal creature.

Here's what I've found: Incorporeal Movement. The specter (or whatever creature) can move through other creatures and objects as if they were Difficult Terrain. It takes 5 (1d10) Force damage if it ends its turn inside an object.

Based on a bunch of ghost stories and examples too numerous to list, common sense would tell me this rule is wrong; and that the spectre (or whatever) can move through other creatures and objects as if those obstacles were not present.

That they take damage if they remain inside an object seems to indicate considerably more interaction with the "real" game world than I'd have expected. That said, there's design space for both: some incorporeal creatures might move freely through obstacles as a creature ability while others have to treat them as difficult terrain etc.

If moving through objects is difficult terrain, and they take damage if they end a turn in an object... it kinda means that they are somehow interacting with surfaces in some way.

This reasoning makes sense to me based solely on what's written. I suspect, thinking quickly about it, the rules are written as they are mostly to prevent PC-side abuse of effects that make them ethereal.

 

[billd91]

Based on a bunch of ghost stories and examples too numerous to list, common sense would tell me this rule is wrong; and that the spectre (or whatever) can move through other creatures and objects as if those obstacles were not present.

That they take damage if they remain inside an object seems to indicate considerably more interaction with the "real" game world than I'd have expected. That said, there's design space for both: some incorporeal creatures might move freely through obstacles as a creature ability while others have to treat them as difficult terrain etc.

This reasoning makes sense to me based solely on what's written. I suspect, thinking quickly about it, the rules are written as they are mostly to prevent PC-side abuse of effects that make them ethereal.

Not just preventing PC abuse. Think of how much trouble a DM can cause with incorporeal undead occupying walls or floors and attacking from a largely unassailable location.

 

[touc]

An incorporeal creature isn’t in contact with any surface or liquid. You need to be corporal to make contact with other corporal objects and substances.

This is consistent with the D&D 5E SRD, which clarified: Tremorsense can’t be used to detect flying or incorporeal creatures.

But, is there any actual written rules that preclude this?

An incorporeal creature "has no body." In essence, it has nothing that would cause a vibration in the ground or otherwise create the movement necessary for an ability that by its very name senses "tremors" (aka a slight earthquake). Its ability to pass through solid objects does not make it cease to be incorporeal. With a rule saying otherwise, it's always incorporeal and can't be detected by a sense designed to detect earth movement.

 

[billd91]

This is consistent with the D&D 5E SRD, which clarified: Tremorsense can’t be used to detect flying or incorporeal creatures.

An incorporeal creature "has no body." In essence, it has nothing that would cause a vibration in the ground or otherwise create the movement necessary for an ability that by its very name senses "tremors" (aka a slight earthquake). Its ability to pass through solid objects does not make it cease to be incorporeal. With a rule saying otherwise, it's always incorporeal and can't be detected by a sense designed to detect earth movement.

That was the 5e.2014 rules. The 5e.2024 has removed the incorporeal part of that rule.

 

[EzekielRaiden]

Based on a bunch of ghost stories and examples too numerous to list, common sense would tell me this rule is wrong; and that the spectre (or whatever) can move through other creatures and objects as if those obstacles were not present.

That they take damage if they remain inside an object seems to indicate considerably more interaction with the "real" game world than I'd have expected. That said, there's design space for both: some incorporeal creatures might move freely through obstacles as a creature ability while others have to treat them as difficult terrain etc.

Well, the idea is that while the ghost is actually incorporeal--as in, it is truly manifested on the Material Plane, with its ghostly body--then it really is interacting with the, as you put it, "'real' game world" to a greater degree. If it instead used its Etherealness ability to shift to the Border Ethereal, and then employed its Ethereal Sight to look up to 60' around itself into the Material Plane, then it would not actually be passing through those objects--it would simply be located at the space in the Ethereal where that object happens to be in the Material.

It's similar to, but of course not identical to, the difference between using plane shift to go to another plane, vs using some kind of scrying spell to merely view the place that corresponds to your current location in a parallel plane. If you plane shift, your body is actually there and has to respect the objects around it. If you simply scry, then the only thing that matters is what objects are near you in your current plane, not the ones in the other plane.

This reasoning makes sense to me based solely on what's written. I suspect, thinking quickly about it, the rules are written as they are mostly to prevent PC-side abuse of effects that make them ethereal.

Almost certainly.

The vast majority of rules are written in a player-facing way, because the player is the one actually using most of those rules. Anything not actually facing the players, so long as it is self-consistent and reasonable, need not bear any similarity at all to player-facing rules. This is not merely a game design convenience, it is the recognition that rules designed for player use usually need to be tighter, cleaner, and more specific, because misuse or abuse is a bigger long-term concern. A monster lasts, what, five rounds? If that, in most cases! A player-facing rule about tremorsense lasts for the entire game's existence. There's less pressure (not no pressure! Just less pressure) to do things Just Right with the monster's rules than there is with the rules actually visible to the players.