As I have rolled forward working on monsters, I have tried to make their interrelations with the world, and frankly the party trying to kill them, a little more practical. This has included things like patterns of attack, such as whether or not the monster focuses its weapons on one target or on many, or how long the monster can be expected to remain in the fight.
I have also, now and then, put a few other features in, such as adding a generator for hit points and stats, or detailing the exact way that a monster's poison works, updating the poison list for those poisons that might be salvaged after the kill. Steadily, I have made my way through strictly the original monster manual to the end of the C's (I'll go back and add other monsters from other books later) ~ and this has brought me to the letter D: demons.
Looking over the general description that Gygax wrote 40 years ago, that was meant to apply to all demons, I recognized at once that there's very little in the description that defines what a demon is. As part of the description of the manes demon, it reads, "Those dead which go to the 666 layers of the demonic abyss become manes." Which dead? What is it about these dead that separate them from dead that go elsewhere? And what of the other, more powerful demons (and the devils also). What makes a demon?
We can return to John Milton and apply the mythology that devils, and perhaps demons as well, are angels that have been cast out of heaven. This, however, only postpones the question, what makes an angel? Milton did not have to worry about this; he didn't have to deal with players who might want to actually make a demon or a devil, or be put in a situation where they have to stop such an event. Milton had it easy.
So I am thinking about that, about what makes a demon, and what separates demons from devils, from a zoologist's perspective, when I realized that before I can even try to answer that question, I have to first define what distinguishes the Abyss from Hell, Gehenna, Tartarus and Hades ... not to mention other lower planes of existence not highlighted by the original alignment chart.
Now, let's be clear. I don't use alignment. For my game, "evil" is a descriptive, not a prescriptive, term. To some degree, everything and everyone of rational intelligence is in some part evil, just as all rational things are in some part good. Evil is a choice, not a character trait ~ and to be specific, the choice is to be malevolent, which derives from the Latin meaning to "wish badness," most likely upon others and upon the world.
This is why deadly spiders are not evil or malevolent; they do not actively wish anything; they merely need to eat or lay their eggs and the poison they carry is an unknowing means to that end. The spider does not wish you harm; it does not know there is a "you" at all.
If I'm going to craft the lower planes, then, it follows that their geographic relationship has nothing to do with having law or chaos as a framework. "Law" is just as much a choice as malevolence. All things that have authority have law; and all attempts at law fail to root out the last vestiges of chaos. Unless Hell features a perfectly ordered society in which all persons in it move in lockstep, without randomness or uncertainty in a completely known universe, there will be chaos there ~ and if you as DM perceive that this might just be exactly what Hell ought to be, to fit your prescriptive framework, well, how boring. I wouldn't want to adventure in your Hell. Where's the wiggle room?
To remain consistent with that rigid, playable framework that is required for a good game, the lower planes must be made flesh from some other sourcework than those applying to D&D alignment ... and thankfully, we have only 2,800 years of general theological supposition to consider.
Let us not forget that Hell, the Abyss, Gehenna, Tartarus and Hades all exist in an academic sense well outside the realm of role-playing games, engendering discussion that is regularly pursued by people other than role-gamers. When I think to figure out what these things truly are ~ and I must admit, I've never really sat down and given it much thought before today ~ I want to go to the source. To the "real" work that has been done.
There is an obvious problem. These things come from different cultures, who all created various destinations to which the dead to travel. Basically, the same dead. There was no distinction made within these cultures that only a certain kind of dead would go to such-and-such a place ... so we must either pick a specific place for all the dead to go (perhaps to be redistributed later, for some reason) or create some factor that defines which dead go to which place, and why. An easy, obvious solution would be to argue that all the Greek dead go here, and all the Christian dead go there, the Elvish dead and the Orcish dead go elsewhere, but to my mind if there really were these planes, why would they care what belief system these beings on Earth had? Is a demon prejudiced? Does a demon send you back if you're not the victim expected?
Not to my mind. And in fact, I have little interest in any distinction that would regulate which dead go to which lower plane based upon what backgrounds they had or how awful they were. We already have such a system established for Hell and Hell alone, written by Dante, and I'm not going to denude certain levels of Hell so that I can outsource murderers or blasphemers to another plane of existence just to be sure the caves there don't go empty. No, I just don't see it that way.
To my mind, it makes no nevermind what carcass you possessed in the prime material ~ you're dead now and it is your essence, not your body, that is burning in the eternal pit of flame; so expect to be sitting in that pit next to an orc, a halfling and a lizard man, because that is just how it goes.
Perhaps I'm ruined by Dante. Hell must be, for me, the arrival gate. Abandon all Hope, Ye Who Enter Here. If there is some reason why the other planes are populated by the dead, it is because of what happened after those dead arrived in Hell. Basically, to my mind, the other planes are parts of Hell, where the dead are selectively routed after it is discovered that they have ... something. Skills? The right attitude? They've been here this long so they're ready to be moved down? Perhaps, in the true Mengelenian sense, there are devils and demons moving through the suffering hordes, selecting this one for experimentation, to create a better beast, to divide and multiply into a more horrific atrocity, and there are specific places where that happens.
If I can establish a movement of the dead, a steady migration out of the planes of Hell and into other planes, where lines of misery can be identified as the swirl of dead are marched into deeper and deeper misery, then I can perhaps figure out the jobs that these demons and devils do ... and ultimately, how they were designed by higher powers in order to do those jobs. From there, it follows that this provides a personality for individual demons and devils that really, really, really doesn't exist in the books, a motivation, that can in turn explain just why these three demons are found standing on this dark streetcorner in the middle of the night when a player character walks by.
I'll be working on this for a while, playing with it, writing a draft on the blog and eventually a final layout on the wiki.