AD&D assumes that the anima,
that force which gives life and distinct existence to thinking beings,
is one of two sorts: soul or spirit.
Humans, dwarves, halflings, gnomes, and half-elves (those beings which can have a raise dead or resurrection spell cast upon them) all have souls;
all other beings that worship deities have spirits.
This latter group includes (but is not limited to) elves, orcs, half-orcs, and the other creatures specifically mentioned in the NONHUMANS' DEITIES section of this work.
The DM may decide on a case-by-case basis whether other creatures have spirits or worship deities;
the only parameter is that monsters with spirits must have at least an intelligence rating of Low.
Please note that the following system is only a suggested one.
Individual DMs should use a different system if they find this one unsuitable.

When a being from the PMP dies, its soul or spirit goes to one of the Outer Planes.
(See THE KNOWN PLANES OF EXISTENCE section.)
Selecting which plane the soul or spirit goes to is the province of the DM, based upon the alignment behavior of the creature during its mortal life.
If a human cleric died professing to be LG, he or she migh expect to go to one of the Seven Heavens.
The DM might judge some of the cleric's acts as more neutral than lawful,
and decide that a more appropriate plane would be Elysium.
If a being has been faithful to the teachings and tenets of its deity, however,
it is likely that the soul or spirit will pass into the plane where the deity resides.
Moreover, the soul or spirit will go to that part of the plane most strongly influenced by the deity;
for each plane is infinite, and most planes have more than one deity residing there (Olympus, Asgard, etc.).

Any difference between souls and spirits lies in what happens to them when they arrive at their destination.
For souls, it is the beginning of eternity;
it is on this plane that the soul will remain forever,
enjoying the benefits or suffering the torments thereof.
Spirits, on the other hand, may be but temporary residents of the plane.
Their rewards and punishments are less than that received by souls.
At some time in the future,
at the will of the deity,
the spirit can be returned to the PMP -- reincarnated.
The new creature will not have any form of overt memories of its former life,
nor will its new form necessarily be the same as its old.
If an elf becomes evil during his or her life,
his or her spirit would go to one of the evil planes at death.
The ruler of that plane might,
a century later,
decide to send the being back as a Drow,
for example;
this Drow would have the same sort of good-evil choices during life as the elf had (albeit from a different viewpoint),
and conceivably could go to yet another plane upon death if he or she did not remain evil and loyal to the master of that place.
The amount of time that a spirit must remain in a plane before returning to the PMP is extremely variable.
It could range from as little as ten years to a millenium or more -- time is not important to a deity.

(Note: The above is only a suggested method for dealing with character life-after-death.
The DM may, of course, use whatever system is most appropriate to his or her campaign.)

There is a time lag between death and arrival at the plane of destination.
Although time is meaningless to the soul or spirit,
the long journey to the proper plane can take 3-30 days of time relative to those in the PMP.
Thus the rationale for the progressive tiem limit on the raise dead spell becomes clear:
the farther the soul has travelled on its way to its destination plane,
the more powerful the cleric needed to summon the soul back to its mortal coil.
The road through the Astral Plane to their destination is clearly marked for the dead,
but is is not free of peril.
Some monsters roam the ethereal and astral planes at will,
which is why burial chambers often include weapons,
treasure,
and even bodyguards to protect the soul on its journey.

A resurrection spell functions in a different manner from a raise dead:
the cleric literally recalls the soul from the plane of its deity back into its former body,
where flesh and blood have been magically restored to the bones.
As this involves the cooperation of the deity on the plane where the soul was,
clerics must use extreme caution in employing this spell.
If a cleric resurrects a being of different alignment simply to serve the purposes of the cleric or his or her deity (to extract information, for example),
the deity on the plane where the soul was may be highly displeased and may take appropriate action.

The servants, functionaries, and minions of some deities (demons, devils, couatl, ki-rin, titans, and others) are actually spirits put into those forms for the purposes of the deity.
It should be noted that the forms listed in the MONSTER MANUAL are by no means the only ones these servants can take --
some chaotic deities rule planes where no two beings have the same form!

Immortality in AD&D does not confer or imply everlasting existence;
in essence what the gods enjoy is eternal youth.
Many of the gods can,
of course,
alter their forms at will and appear young or old;
though this appearance is sometimes dictated by their followers (the ruler of a pantheon should appear older, wiser, and more mature than, for example, a god of mischief).
Any description of gods as "young" or "old" is at best extremely relative and has no bearing on their powers.
A character who obtains apparent immortality through many potions of longevity need not fear death through "natural causes" (until he finally drinks the potion that reverses the effects of all the previous ones), but can still be slain by normal means.

When deities or their minions travel to planes other than their own,
they mystically anchored to their home plane by a metaphysical "silver cord";
this is similar to the one described for astral spell,
but cannot be broken by the Psychic Wind or any other means.
This cord is what pulls a spirit back to its plane of origin when its material form is destroyed.
The return occurs near-instantaneously,
in contrast to the trek of a soul.
The energy expenditure of this is enormous,
and will weaken the returning being:
servants, devils, demons, and even the deities themselves.
Thus Type V and Type VI demons must rest a century before returning unaided to the plane where they were slain (see MONSTER MANUAL);
demon princes and lords, and greater devils and arch-devils require 2-8 weeks to restore their energies to a point where they can plane travel or send a servitor to another plane;
and even greater deities require 1-4 weeks of rest before dealing with activities outside their home plane.
During this dormant period, it will be impossible for any clerics of the resting deity to acquire or recover any spells of third level or higher;
this may be interpreted with dismay by the deity's earthly followers as a bad omen,
but no information will be forthcoming until the dormancy is over (and even then it's unlikely that a deity would admit to its followers that it had been defeated!).
It is important to remember that when a deity "dies" on the PMP,
the being's person and possessions fade away and disappear,
though certain items may remain (at the DM's discretion).

If any servant or minion of a deity (or even the deity itself) is slain on its home plane,
that being is absolutely and irrevocably dead.
No power in the multiverse can restore that being,
including action by other deities.
In one's own plane a being a figuratively backed into a corner,
with nowhere for the spirit to go upon death.
All creatures are most powerful in their own territory,
so it should be next to impossible for anything except for another deity to slay a deity on its own plane --
and direct confrontation between deities is extremely rare.
Should mere characters be so brazen as to challenge a deity on its home plane,
they should be dealt with severely,
the god bringing to bear all the powers that the being has.

Humans, dwarves, halflings, gnomes and half-elves (those beings which can have a raise dead or ressurection spell cast upon them) all have souls;
all other beings that worship deities have spirits.

Although time is meaningless to a soul or spirit, the long journey to the proper plane can take 5-30 days of time relative to those in the Prime Material Plane.
Thus the rationale for the progressive time limit on the raise dead spell becomes clear: the farther the soul has travelled on its way to its destination plane, the more powerful the cleric needed to summon the soul back to its mortal coil.

A ressurection spell functions in a different manner from a raise dead: the cleric literally recalls the soul from the plane of the deity back to its former body, where flesh and blood have been magically restored to the bones.
If a cleric ressurects a being of radically different alignment, the cleric's deity (who gave the cleric this power) may be greatly offended.
Similarly, if a cleric ressurects a being of different alignment simplty to serve the purposes of the cleric or his or her deity (to extract information, for example),
the deity on the plane where the soul was may be highly displeased and may take appropriate action.

A character who obtains
apparent immortality through many potions of longevity need not fear
death through "natural causes" (until he or she finally drinks the potion
that reverses the effects of all the previous ones), but can still be slain by normal means.

When deities or their minions travel to planes other than their own, they
are mystically anchored to their home plane by a metaphysical "silver
cord"; this is similar to the one described for astral spell, but cannot be
broken by the Psychic Wind or any other means.

Thus Type V and VI demons must rest a century before returning unaided to the
plane where they were slain (see MONSTER MANUAL);
demon princes and lords, and greater devils and arch-devils require 2-8 weeks to restore their energies to a point where they can plane travel or send a servitor to another plane;
and even greater deities require 1-4 weeks of rest before dealing with activities outside their home plane.
 

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Also what is the definition of a soul and spirit in game terms?
We know which beings have souls and spirits and those with sprits can't be raised/resurrected, but what, if any, are the definitions of each?

Only humans humans have souls. All living things might have spirits. Deal with such metaphysical questions as the differences between soul and spirit as you see fit. the Egyptians believes that a human had a soul, spirit, shawow, double, name, and two other components in his makeup. This is about a game, isn't it? Thus I don't attempt to deal with such esoterica in rules interpretation :roll:

Quote:
I asked these in the past tense so to get the original intent of your rules/thoughts, not as to a rules interpretation of a game currently under the realm of WotC. :wink:
 

Sorry that my original intent wasn't evident, and I hope that my answers above will assist in conveying that now.

Cheers,
Gary