GUSMAET (Grand Unified Soul, Matter And Energy Theory) - LONG
GUSMAET is pronounced "Goose Mate" LOL... but here goes...
An interesting question. Let's try defining some terms and put forth some assumptions and see what happens...
Body - Physical, tangible, form (this one seems pretty clear)
Soul - The self-aware sentience (for fans of OSC, the "aiua", IIRC)
Let us assume that the main "inner planes" are not fourfold, but sixfold:
Positive Energy
Earth, Air, Fire, Water
Negative Energy
The methods of animation of the "body" are various and sundry, and I will try to keep things in line with default D&D cosmology, which tells us that Elementals and Outsiders cannot be raised if slain. Presumably, their souls are not lacking - since they are sentient - but are rather inextricably tied to their bodies.
We know that positive energy is considered "healing energy" for living creatures, while negative energy "disrupts life."
Presumably, the outer planes, in addition to being made of Earth, Air, Fire, and Water - may also be thought of as being made of "Law and Chaos, Good and Evil." Hence, there is matter that is "Law" etc.
Let us consider first the easiest case - elementals. Elementals are creatures that are sentient (have a soul), are composed of matter from the inner planes (Earth, Air, Fire, Water), and cannot be raised if slain - hence, the soul must be inextricably linked to their body. This tells us that Earth, Air, Fire, and Water are "media" capable of "holding" the soul. Further, elementals can be "healed" by either positive energy (normal healing spells) or in some cases by application of their native element - at least in prior D&D versions.
I will posit that, consistent with the above, positive energy can be converted into Earth, Air, Fire or Water - but only when applied to a living being. Now, of course, I have to define a living being. LOL
Well, to me, the option that is most attractive for defining "what makes a soul," given the above, is that the soul is a "wave pattern," if you will - something that is not the media itself, but relies upon the media for its continued existence (clearly, you can have water without a wave, but you cannot have waves without water). It is this pattern, this organization, that differentiates between a sentient earth elemental and a big, earth-elemental-sized lump of matter from the elemental plane of earth. Contained within the pattern is not only the sentience of the creature, but at an unconscious level, "instructions" for how the creature's body behaves - hence, when positive energy flows into the pattern, it automatically transforms itself based upon the pattern into the needed physical elements, "healing" the body of the elemental. Similarly, a large enough disruption of the medium is sufficient to disperse the pattern - in more D&D-ish terms, inflicting enough damage and ruining enough of the body "breaks" the pattern and kills the creature.
This further tells us that pure elemental material is not good at "holding" patterns - left to itself, it collapses to a "raw" state, devoid of patterns (precluding raise dead spells from working even a moment after the creature's death). We can therefore define a "living" creature as one whose tangible body is imbued with a sentient "pattern."
Outsiders, which work in much the same way as elementals, lead us to believe that Law/Chaos/Good/Evil matter works the same way as Air/Earth/Fire/Water matter. So Law/Chaos/Good/Evil are media capable of propogating the necessary "patterns" of the soul, but do not do a good job of holding the patterns.
Having played with all of these thoughts, let's turn our attention to the problem of humanoids and other creatures which CAN be raised and DO have souls that can exist independent of the body. We have already established that elements such as Air, Earth, Fire, and Water and Law, Chaos, Good, and Evil are not "stable" enough media to continue to hold a soul in the face of severe disruptions (damage) to the elements in question. This leaves us with two other media to explore - positive and negative energy.
Given the effects of positive and negative energy on living creatures, it should be rather obvious that for living creatures, the only logical choice for a medium is positive energy. We further know that the bodies of living creatures are (in theory) composed of a mix of air, earth, fire, and water - and also Law, Chaos, Good, and Evil - that's the tangible "stuff" - while positive and negative energy are intangible. Since the material elements themselves do not "hold the pattern" of sentience (rather, positive energy does) in the case of living creatures, it seems reasonable that positive energy could be called the animus (animating force) of the creature - hence, positive energy must have some connection to the eight physical elements. We won't examine this connection here - it is enough to say that positive energy can animate the eight physical elements - but only when that energy contains a sentience pattern - a "soul" independent of the body itself.
This sets us up for a lot of nice "features" in the D&D system. The positive energy pattern itself is tied to the body through connections - which, when enough of the connections are severed, causes the positive energy and the pattern associated therewith (the "soul") to separate from the body. Does this look like "hit points" to anyone else? Furthermore, positive energy poured into the creature can be used to (a) re-establish/strengthen the "soul" (in cases such as Int/Wis damage) or (b) be converted per the directions extant in the soul pattern into "material" element. (a.k.a. healing). Since Int/Wis damage heals naturally over time just as physical damage does, it seems to imply that positive energy has the natural property of "regenerating" itself over time as necessary to fill out the sentience pattern.
If we assume that the pattern "prefers" to acquire certain material elements - or to convert positive energy into those elements - suddenly, we see "alignment" falling out of this world view as well. The patterns of some individuals could be - or become through choices, depending on how you look at it - predisposed to acquire Law matter and expel Chaos matter... meaning that over time, the creature's body literally becomes "Lawful." (Repeat, substituting in alignment axes of your choice) - or it may have no preference, so that on balance, the body stays "neutral." Now, the "detect evil" spell doesn't look quite so silly - it's simply detecting for a certain type of matter - and the small amount of "evil matter" in a "Good" character will be masked by all the "good matter." Similarly, we can get "prime material" creatures with subtypes as they naturally collect certain elements to the exclusion of others (perhaps frost worms, with a Cold subtype, have expelled nearly all "Fire matter" from their beings).
Some of the other consequences of this idea of the nature of creatures in D&D? Well, let us further ascribe to positive matter free of the "dimensional anchor" of a physical body the ability to "plane shift" over time towards the outer plane towards which its "preferred alignment" pre-disposes it. In common terms, let's say that the "soul," when separated from the body, has a natural tendency to seek the outer plane appropriate to its alignment. Once it arrives in that plane, which is "conducive/friendly" to the matter the soul prefers, the positive energy slowly converts itself into the appropriate type of matter (in the case of Neutrals, it converts itself into equal amounts of Law/Chaos and/or Good/Evil matter). Suddenly, "petitioners" from MotP have "fallen out" as a natural result of our assumptions - and we see why heaven and hell fight for souls - the only way to add significantly to the population of the outer planes is through the natural gravitation of souls formed of positive energy to the outer planes... since the amount of matter in the outer planes is otherwise constant (huge, but finite), there is an upper limit on the number of progeny members of the outer planes can have amongst themselves... but positive energy that changes into "aligned" matter is very much "new" matter and in a very real sense increases the "power" of the plane.
Similarly, creatures that "store/eat" souls are creatures with the ability to somehow interact with the positive energy that makes up a soul... and hence can disrupt or even destroy the "pattern" that resides in/on the energy.
Another interesting consequence - and this is the one that finally attempts to answer the original question - comes if we assume that negative energy is just as capable of holding patterns as is positive energy - but with the stipulation that negative energy is a more "degenerate" form of energy than positive energy and cannot transform itself into matter. In other words, it's a one-way street - positive energy can become matter can become negative energy, but not the reverse. Now we can attempt to handle the undead question.
1.) Non-intelligent undead - Lacking sentience, but given animus by negative energy, these undead are "moved" by negative energy that does not have an associated sentience pattern. The soul is still independent of the body, and IMO, has the ability to be raised by spells that do not require the original body.
2.) Intelligent undead spawned from creatures that are killed (e.g., ghouls, wights) - These creatures have sentience, but it is somewhat bestial and imperfect. Presumably, the "sentience pattern" in the negative energy of these creatures is one that is "trying to fit" the body that it has - and not being the original "shaper" of the body, cannot do so easily - this "mis-fit" causes problems such as low intellect, as the energy is not nearly as much in control of the body as it would like to be. Again, the soul is still independent of the body, and IMO, has the ability to be raised by spells that do not require the original body.
3.) Intelligent undead that are "Transformed" from the living (e.g., vampires, liches) - These creatures are in perfect control of their bodies - because rather than try to fit an energy pattern onto a body, they simply substituted - willingly or unwillingly - slowly or quickly - the positive energy on which their sentience pattern was overlaid with negative energy. Thus, there has been no discontinuation of sentience - merely a replacement of the media on which that sentience rests. These creatures' souls are literally made of negative energy instead of positive energy. Some creatures (such as liches) bind their souls to phylacteries as well as physical bodies - the details of this are beyond the scope of this examination - let's just say, "it's magic" - since it literally is magic that is used to effect this change. The question of, "does a vampire's soul disperse or go to the outer planes when it is destroyed?" is one left to the individual DM, I suppose... does negative energy behave like positive energy in this manner? There's no hard evidence one way or the other, but I would suggest that the soul instead gravitates to the negative energy plane - where it succumbs inevitably to madness, crushed up with all the other souls there and without a physical body... until it returns to be animus for a semi-intelligent undead (#2 above)... which explains where those patterns come from in the first place and why they "don't quite fit" their (new) bodies.
It also explains why only the most powerful of resurrection/raise spells DON'T require a body - the soul is attuned to certain elements and only powerful magic can assist it to the degree necessary to create a new body in the right proportions whole cloth out of physical materials. The magic "helps" the soul create matter to "fill in the blanks" under ordinary circumstances - which is why you need fresher, more complete corpses the weaker the magic used.
Incidentally, the reason that possessions, et al, works, can be attributed to magic "bridging the gap" - the above is based on a "natural world" view - and magic can of course be used to "fake" a better fit of body to soul during possession, etc. We can actually let that stand as a the "hand-waving" method to questions outside the natural life/death/undeath order - if it's not covered in life/death/undeath, "it's magic."
CONSTRUCTS: Matter animated by Magic. Depending on the matter involved, may have a subtype.
PLANTS: Tough one. Intelligent ones follow these same assumptions, perhaps non-intelligent plants are like non-intelligent undead - animated/given life by positive energy without a pattern.
NIGHTSHADE: Perhaps an unholy creature native to the negative material plane? As such, it fits the definition of undead espoused above (one whose animus/soul is made of negative energy) - perhaps with a body made mostly of negative energy, with only Evil physical matter.
GHOSTS AND OTHER INCORPOREAL UNDEAD: Perhaps their bodies are made of "ether" - a ninth element - rather than the eight physical elements.
Wow, that was a lot longer - and more comprehensive - than I thought it would be. And probably riddled with bad assumptions and faulty logic and stuff inconsistent with core D&D.
Thoughts? Critiques? Comments? This was all done "off the cuff" without reference to D&D books and is the first time I've tried to address the question from start to finish in a comprehensive fashion.
--The Sigil
