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In the D&D 5e group I'm playing in we're currently wondering how much our characters (all level 7) would know about the planes in the Forgotten Realms campaign setting (we're playing SKT, though that's otherwise not relevant to the question).

The knowledge in question is only that about the basics of the Great Wheel Cosmology, as described in the PHB in "Appendix C: The Planes of Existence", pages 300-303.
Detailed information about a certain plane, planar creatures or planar politics (i.e. the blood war) obviously requires either a knowledge check or a backstory reason why the character would know this particular kind of information (i.e., a Githzerai character sent from his home in Limbo to fight Mindflayers on the material plane would obviously know about Limbo and its workings).
Chapter 7 of the PHB, "Using Ability Scores", also specifies that the Arcana skill is meant for checks concerning the planes (see quote below), but not whether you need it to know that planes are a thing.

Arcana. Your Intelligence (Arcana) check measures your ability to recall lore about [...] the planes of existence, and the inhabitants of those planes.

That being said, for the purpose of this question, assume that there are 3 different types of people:

  • people with proficiency in the Arcana skill
  • spellcasters without proficiency in the Arcana skill
  • non-spellcasters without proficiency in the Arcana skill
  • run-of-the-mill commoners

Which of the following facts about the Great Wheel cosmology would be known to average representatives of these 4 types?

  1. planes of existence are a thing / there's more than just the material plane
  2. the overall "layout" / names of the planes, as specified in the PHB on page 303
  3. the distinction between demi-, transitive, inner and outer planes and how they differ from each other
  4. methods of planar travel

Clearly, spellcasters - even without Arcana proficiency - have to have at least basic knowledge, otherwise, it wouldn't make much sense to have access to spells such as Banishment (lvl 4), Contact Other Plane (lvl 5) or Plane Shift (lvl 7). Or would you be unable to cast these spells if you don't have knowledge about planes?


I'm primarily interested in any guidance given in official sources, whether they're rulebooks, novels, developer tweets or something else. Since my group is playing 5e, sources for that edition would be preferable, but ultimately, sources for any edition are fine.

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closed as primarily opinion-based by screamline, Miniman, KorvinStarmast, Ruse, Purple Monkey Dec 31 '18 at 1:16

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ I've decided to use the [dnd-5e] tag, since 4e used a different cosmology, and I don't know how much pre-4th-edition's versions of the planar cosmology differ from the 5e version. If you do know, and you believe the generic [dungeons-and-dragons] tag would be more suitable, feel free to change it. \$\endgroup\$ – PixelMaster Dec 30 '18 at 22:35
  • \$\begingroup\$ I am not sure if there is such a thing as an average adventurer. You did include level (good) but even that leaves us wide open if we consider backgrounds having such a broad range of "before adventuring skills and knowledge." Without being a scientist, were you familiar with the periodic table of the elements before you left high school? What reason have you given for the average denizen of Faerun not knowing what is in the PHB? (That is the player's resource ...) \$\endgroup\$ – KorvinStarmast Dec 31 '18 at 0:49
  • \$\begingroup\$ @KorvinStarmast I personally think that the average denizen would know, but since (as far as I'm aware) not everything in the PHB is automatically in-game character knowledge, our group just wasn't sure (until the DM gave a clear answer, which was after I posted this question). But yeah, I can see where the close votes are coming from, it probably is a very situation-dependant question. \$\endgroup\$ – PixelMaster Dec 31 '18 at 1:18
  • \$\begingroup\$ Yeah, some of the groups I play with have a norm: if it's in the PHB, the players know it. But that I am sure varies table by table ... \$\endgroup\$ – KorvinStarmast Dec 31 '18 at 1:23