Are the positive and negative planes inner or outer planes in the Great Wheel cosmology model?
I'm unsure of which they are in the 5th edition Great Wheel cosmology model. I know they are inner planes in other models.
As specified in the DMG on 43, 5e has several "categories" of planes:
- The Material Plane and Its Echoes. The Feywild and the Shadowfell are reflections of the Material Plane.
- The Transitive Planes. The Ethereal Plane and the Astral Plane are mostly featureless planes that serve primarily as pathways to travel from one plane to another.
- The Inner Planes. The four Elemental Planes (Air, Earth, Fire, and Water), plus the Elemental Chaos that surrounds them, are the Inner Planes.
- The Outer Planes. Sixteen Outer Planes correspond to the eight non-neutral alignments and shades of philosophical difference between them.
- The Positive and Negative Planes. These two planes enfold the rest of the cosmology, providing the raw forces of life and death that underlie the rest of existence in the multiverse.
The sidebar and image on p.300 of the Player's Handbook, and the more detailed drawing on p.303, indicate that the energy planes are neither "Inner" nor "Outer", but beyond both. The Dungeon Master's Guide gives a list of categories for planes (p.43) which lists the energy planes as a category of their own:
The Positive and Negative Planes. These two planes enfold the rest of the cosmology, providing the raw forces of life and death that underlie the rest of existence in the multiverse.
Based on that description, positive and negative energy are potentially the most basic aspects of all creation, and everything else, from the divine planes to the elemental and material, are expressions of the interplay of those two forces.
While the DMG's chapter 2 discusses most of the planes in at least broad strokes, there's virtually no information given about the actual nature of the energy planes -- not even the most basic statement of what it's like there and what things or places might be there. This suggests to me that the enegy planes lack the physicality necessary to travel there, or at least there isn't much point to doing so, because it would be simply an immaterial void containing nothing and no one. (The Wand of Orcus artifact does mention going to the Positive Energy Plane as part of its convoluted method of destruction, but that is the only mention of the Positive Energy Plane being a place you can go.)