I am trying to understand from a RAW point of view as to how the interaction between the spell Fog Cloud interacts with the errata'd rules of vision and lighting.

First, we have the normal vision rules for heavily obscured:

A heavily obscured area–such as darkness, opaque fog, or dense foliage–blocks vision entirely. A creature effectively suffers from the blinded condition (see appendix PH-A) when trying to see something in that area.

Next, we have the errata:

Vision and Light (p. 183). A heavily obscured area doesn’t blind you, but you are effectively blinded when you try to see something obscured by it.

As we know, Fog Cloud creates an area of heavily obscuring fog around the effect zone. According to the errata, it would seem as if being inside the fog does not blind you, hence, you can attack creatures outside of the fog with advantage as per the unseen attacker rules.

Am I understanding this correctly? An I missing something?

Please advise, and thanks in advance.

  • \$\begingroup\$ To clarify for others, this change was made in the very first errata in 2015, not the 2017 errata currently linked in the question... The "normal vision rules for heavily obscured" quoted in the question reflect the wording of those rules post-errata. Originally, that paragraph of the rules said (emphasis mine): "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 appendix A)." \$\endgroup\$ – V2Blast Aug 4 '19 at 4:16
  • \$\begingroup\$ FYI, the new text reads: “A creature effectively suffers from the blinded condition (see appendix A) when trying to see something in that area.” \$\endgroup\$ – Guillaume F. Jan 4 '20 at 0:03

The fog cloud spell says (emphasis mine):

You create a 20-foot-radius sphere of fog centered on a point within range. The sphere spreads around corners, and its area is heavily obscured. [...]

Unlike nonmagical darkness, other heavily obscured areas created by spells such as fog cloud do generally prevent creatures from being able to see through them (unless there is some feature, spell, magic item, etc. that allows them to do otherwise - such as the warlock's Devil's Sight eldritch invocation when it comes to the darkness spell).

The distinction is that nonmagical darkness doesn't involve stuff blocking your vision, just the absence of light in that area. If there's a light shining down at point A and another at point B, and there's a bit of mundane darkness in between (but nothing else obstructing your view), then nothing prevents you from seeing the light at point B if you're standing at point A. In contrast, if there's a bunch of fog (whether mundane or magical) between A and B, it may be harder (or even impossible) for you to see B from A.

(Note that this relies on a common-sense interpretation of nonmagical darkness - the rules don't draw such a distinction, presumably because they expect people to apply logic and common sense in understanding how regular darkness works.)

As such, a creature in the middle of the fog cloud would be unable to see a creature outside the cloud, just as the creature outside would be unable to see the creature within the cloud. If one attacked the other, the attacker's advantage from being unseen would be canceled out by their disadvantage from being unable to see their target.

  • \$\begingroup\$ Does this mean that although it is not expressed explicitly, there is a clear distinction between complete heavy obscurement (such as a fog) and partial heavy obscurement (such as being on the shadow of a long unilluminated corridor)? \$\endgroup\$ – Throbs Harper May 11 '18 at 4:03
  • \$\begingroup\$ @ThrobsHarper The terms used in the PHB are "heavily obscured" and "lightly obscured" and yes there is a difference. But there is no such thing as partial or complete obscurement. There is partial or complete cover, but that is a different mechanic. \$\endgroup\$ – Rubiksmoose May 11 '18 at 16:33
  • 2
    \$\begingroup\$ I think the key is to use common sense when it comes to nonmagical darkness. Nonmagical darkness doesn't prevent you from seeing something lit on the other side of it; it doesn't prevent light from passing through. Magical darkness and other spells that create heavily obscured areas do, because they obscure the area in between you and the point you're trying to look at. \$\endgroup\$ – V2Blast May 11 '18 at 17:32

By RAW, you are only affected by the penalties of heavy obscurement if you are trying to see inside of the heavily obscured area. You are correct in interpreting the rules as saying a creature within a fog cloud can clearly see outside of the fog cloud because the spell states it creates an area of heavy obscurement and the rules for heavy obscurement specify that you are only penalized when attempting to see something in the area of heavy obscurement. If you were to explain this logically you might say that objects within the fog cloud are blending in with the wisps of fog that are swirling around in the spell's effect, whereas objects on the other side of the fog cloud are being hit by more light and although the light is being blocked from hitting your eyes due to the fog cloud you are at least able to make out shape and form better than if the object was surrounded in fog.

Although I think this is the correct RAW interpretation, I don't think these rules work intuitively or that they are a good representation of how the situation would play out in the real world. I think if you wanted to alter it to be more real-world accurate you would add that you suffer from heavy obscurement penalties while trying to see inside of a heavily obscured area as well as when trying to see from within the area of heavy obscurement. However, although I think the rules by RAW are not a good simulation of the real-world I still think they work as intended as the image of a group of archers or spearmen hocking projectiles from the fog seems like a very evocative image to me.


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