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Here's the scenario:

  • Creature A is invisible, in an empty room, in an arbitrary location in the room
  • The room is adequately lit (call it Bright Light, for the sake of argument)
  • Creature A is trying to hide (they make a Stealth Check).
  • Creature B enters the room.
  • Creature B is not actively searching for Creature A, so their Passive Perception is compared against Creature A's stealth check.

Does Creature B's Perception check have Disadvantage?

Answers should not make assumptions about what the rules should do or what they were intended to do. Nor should they make assumptions about how rules interact with each other. Please stick strictly to the rules as written only.

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  • \$\begingroup\$ I think a related question (which might already be answered elsewhere) is whether an invisible creature has advantage on their Stealth check. \$\endgroup\$ – Ryan C. Thompson Mar 22 at 22:03
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    \$\begingroup\$ It seems to me that there's a point missing between your (current) 4th and 5th bullets: what's the determination that the GM made as to whether the attempted task is even possible? (DMG p.237) \$\endgroup\$ – nitsua60 Mar 22 at 22:12
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    \$\begingroup\$ Until the RAW meta is settled we should still be using the tag per its listed tag description. My understanding of our current usage is still that tags are not for dictating the form of answers and thus this is not an appropriate way to describe the use of the tag. I've clarified your language to make that clear and I've left the tag because it does seem to fit how some use the tag. \$\endgroup\$ – Rubiksmoose Mar 22 at 22:50
  • \$\begingroup\$ (The meta in question: Time to retire the [rules-as-written] tag?) \$\endgroup\$ – V2Blast Mar 23 at 0:45
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There need not be any rule that specifically says you have disadvantage.

By RAW, circumstances can impose disadvantage on any check.

You usually gain advantage or disadvantage through the use of special abilities, actions, or spells. Inspiration can also give a character advantage. The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result.

I mention this because I'm going to argue that the rules justify applying disadvantage here, even if they don't overtly require it.

Heavy obscurement is strictly more obscuring than light obscurement.

This is the part you're not going to like, so let's get to it.

Both kinds of obscurement are defined largely by example, and the sets of examples are parallel: Dim light, patchy fog, and moderate foliage are lightly obscuring; darkness, opaque fog, and dense foliage are heavily obscuring. The examples clearly show that heavy obscurement is like light obscurement, only more so.

Therefore there should be no case where anything is more visible under heavy obscurement than it would be under light obscurement. Anything that you can't see in dim light, you also can't see in total darkness.

The Hiding rules say that being heavily obscured has an effect.

One of the main factors in determining whether you can find a hidden creature or object is how well you can see in an area, which might be lightly or heavily obscured, as explained in chapter 8.

Finding a hidden creature involves a Perception check, so there must be some impact on the Perception check (or the Stealth check, but note this also applies to a hidden object, which likely wouldn't get a Stealth check).

The check doesn't automatically fail.

This point was made in Xirema's answer, but to restate it: detecting a creature's presence doesn't require sight and therefore doesn't always fail under blindness or heavy obscurement.

(Except when it does. A creature like a dormant gargoyle might give no signs of its presence except that you can see it, and if heavily obscured, would be truly undetectable.)

Light obscurement imposes disadvantage on detecting a creature's presence.

Perception checks that "rely on sight" have disadvantage in a lightly obscured area. (Note that the rule isn't "require sight".) Most of us could locate another person in a dark room by sound, but as a practical matter we rely on sight to do this.

Conclusion: the Perception check to locate a heavily obscured creature must be at least as hard as rolling with disadvantage, but there's no rule that it's any more difficult than that. The game mechanic that best fits in that space is to roll with disadvantage.

Finally, I think this needs to be said:

The text is not written to be used this way.

You say that you aren't interested in what the rules are intended to do, but that's essential context for reading them at all. The Player's Handbook is a handbook. It explains how to do a thing, namely, how to play the game. It is not a legal code or a set of tournament rules.

None of the rules mentioned here rigorously define their terms. In particular, the obscurement categories are specified mostly by a handful of examples. We had another question going recently about whether partial fog and dim light combined count as heavy obscurement, and the rules give us no way to answer that.

Similarly, if you're blind, you automatically fail "any ability check that requires sight", but ability checks don't say when they require sight. You have to figure that out case by case.

There are also some consequences of this situation that are far more obvious than "disadvantage on Perception checks" but aren't spelled out in the rules. For example, the Blinded condition says you can't see. This causes you to automatically fail at checks that require sight, but what about, say, reading a newspaper? There isn't a check for you to automatically fail, but still, you can't see. To grasp the implications of the rule, you have to apply logic and experience.

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  • \$\begingroup\$ Just a note: Xirema's answer is a self-answer to their own question. Just mentioning it since you referred to it as "Xirema's answer" and not "your answer" :P \$\endgroup\$ – V2Blast Mar 24 at 6:15
  • \$\begingroup\$ @V2Blast I saw it, but thanks. \$\endgroup\$ – Mark Wells Mar 24 at 6:41
  • \$\begingroup\$ Gonna select this as the accepted answer because frankly, the fact that my answer was allowed to accrue a positive quantity of upvotes is a deep shame. I'd rather visitors that arrive on this site see this answer first than mine. \$\endgroup\$ – Xirema Mar 24 at 7:17
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The check would be made normally

I've assumed for a long time that these kinds of perception checks would be made with Disadvantage because of the inability to see the invisible creature, but upon further investigation of the rules, I cannot find evidence that this is the case, and I've had difficulty finding questions on this stack that clearly deal with this case. A lot of answers presuppose that the check is made with disadvantage without actually proving it or questioning whether that's the case.

Not casting aspersions on that answer, FYI, since that's not what that answer is about.

Here is why I believe the check is not made with Disadvantage.

The Invisible condition does not expressly say it confers Disadvantage on Perception Checks

  • An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature's location can be detected by any noise it makes or any tracks it leaves.
  • Attack rolls against the creature have disadvantage, and the creature's attack rolls have advantage.

Invisible, PHB, pg. 291

You might be wondering, dear reader, whether the bolded part (emphasis mine) about the invisible creature counting as "Heavily Obscured", ought to prove that this check should definitely be made with Disadvantage. After all, Heavy Obscurement says that creatures have disadvantage on Perception Checks, right?

The rules for Heavy Obscurement do not say they confer Disadvantage on Perception Checks

In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.

A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition (see the appendix). A heavily obscured area doesn't blind you, but you are effectively blinded when you try to see something obscured by it.

Light and Vision, PHB, pg. 183

Oh.

A Blinded creature is described as automatically failing any check that requires vision; but it makes no mention about Disadvantage on Ability checks which merely make use of vision (Search using hearing, smell, etc. in addition to vision):

  • A blinded creature can't see and automatically fails any ability check that requires sight.
  • Attack rolls against the creature have advantage, and the creature's attack rolls have disadvantage.

Blinded, PHB, pg. 290

And just to make sure no stone is left unturned, the Perception skill doesn't expressly call out Disadvantage on checks which require multiple senses, but for which only one sense is functional:

Your Wisdom (Perception) check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses.

Wisdom Checks, PHB, pg. 178

The rules for Perceiving Hidden Creatures mention vision impairment like Dim Light or Fog, but not Invisibility

What Can you See?. One of the main factors in determining whether you can find a hidden creature or object is how well you can see in an area, which might be lightly or heavily obscured, as explained in chapter 8.

Hiding, PHB, pg. 177

I want to comment on this especially because detecting an Invisible creature isn't necessarily just about seeing it: it's also about detecting evidence of it. Things like footprints or disturbed dust on the ground. Things that would be necessarily harder to detect in a dimly lit room or darkness than they would be in bright light. And of course, there's also the issue of attempting to hear or smell an Invisible + Hidden creature, neither of which are impaired by vision.

The rules for Hiding call out Invisibility as a way to guarantee the option of hiding, but do not call out any benefits to the check

You can't hide from a creature that can see you clearly, and if you make noise (such as shouting a warning or knocking over a vase), you give away your position. An invisible creature can't be seen, so it can always try to hide. Signs of its passage might still be noticed, however, and it still has to stay quiet.

Hiding, PHB, pg. 177

Conclusion: This can't possibly be right, can it?

I mean, that's really weird, right, if an invisible creature is not actually conferring disadvantage on attempts to detect it? If the spectrum of these perception checks is really just the binary of

  • Make the check without Disadvantage, or
  • Auto-fail the check, because of effects like Pass without Trace and/or Silence, suppressing both hearing and other tertiary effects which might leave evidence, leaving only the [in-]ability to actually see the Invisible target

But if there's evidence that definitely disproves this reading, I haven't found it.

Addendum: the creature is still "Unseen", and still confers Disadvantage/Advantage to Attack rolls

Just so it doesn't go unstated: none of this permits a creature to "see" an invisible creature. As far as I can tell, that has not been violated by my understanding of the rules. The only thing that has happened is that the invisible creature's location has been detected (or not detected) based on the results of the Perception Check.

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    \$\begingroup\$ Just out of curiosity, is this how you handle Perception checks at your table? \$\endgroup\$ – Mark Wells Mar 22 at 23:44
  • \$\begingroup\$ In Pathfinder, invisibility gives a +40 to Stealth checks vs. perception, and a +20 if the creature is moving. Again, in Pathfinder (and so maybe not entirely useful here), if the creature is acting "blind" that could also be the disadvantage, that would be a -4 to attack rolls vs. a creature he knows is there but can't see. Essentially: blind fighting--is there such a thing in 5e? If so, that could be an interesting point to throw in here. \$\endgroup\$ – TigerDM Mar 23 at 1:08
  • \$\begingroup\$ @TigerDM unfortunately there is no such corollary in 5e \$\endgroup\$ – Rubiksmoose Mar 23 at 12:23
  • \$\begingroup\$ @MarkWells The context of this question is that up until a few days ago, I had been giving Perception Checks disadvantage against Invisible targets, but closer inspection of the rules suggested this was not RAW. I put out this question and answer because I'm trying to find clear evidence that my RAW understanding is incorrect, and in order to do that, I need to first present my case for what that understanding is. \$\endgroup\$ – Xirema Mar 23 at 19:32
  • \$\begingroup\$ Your understanding is correct and RAW is not weird at all. There's no firm rule because sometimes Creature B is a blind dog, or Creature A is standing in a pool of water, or Creature A is holding a non-invisible item, or because it is a game where anything can happen and DM's make calls based on infinitely varying other circumstances. DM's are intended to confer disadvantage when appropriate, which would be most vision-dependent creatures trying to perceive an invisible creature most of the time. It would be weirder to have a firm rule that had to be remembered and frequently overruled. \$\endgroup\$ – Benjamin Olson Mar 24 at 6:27

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