I've been thinking lately about how alignment will work in my campaign. Alignment has been a problematic concept in D&D for as long as I've been gaming, and I feel the need to codify just exactly what it is and what it represents.
I think a part of the problem is that it models several different concepts that are only tangentially related. On the one hand, it tells you which side you are on in the grand cosmic struggle for the fate of all reality - in other words, who you are aligned with. On the other, it gives you guidelines and boundaries that define a character's behaviour. It's a nebulous concept, and yet it's also concrete due to the fact that it can be detected by magic. I'm big into finding rationalisations and explanations for this kind of stuff, even if those explanations are pure nonsense. So long as it all makes sense in my own head, that's good enough for me.
So I put my head to the problem, and came up with a solution inspired by an article that Gary wrote in The Dragon #8. This article lays out a lot of stuff about the Outer Planes, and particularly focuses on their relationship to monsters and magic weapons. The article theorises that magic weapons extend into the planes, and from there it comes to the conclusion that if there are magic weapons designed to work better against a specific type of creature, then every type of creature must have its own pocket dimension, in which rests a part of its existence. It's heady stuff, and really hard to condense and explain, but it's definitely worth a read.
The idea that every creature type has a pocket dimension got me thinking that there could be a plane for each alignment. I don't even need to create new ones, because that's the very idea behind D&D's planar cosmology to begin with: each of the Outer Planes is keyed to a certain alignment already. My conclusion is very simple. A being's soul resides not completely in its own body, but partially in the Outer Plane that corresponds to his alignment. They are born with no alignment to speak of, and their behaviours as they grow up determine where their soul resides. The soul is not beholden to that plane, though, and a change in behaviour can shift it around - unless magic comes into play. Certain magic items (such as a helm of alignment change) can lock the character's soul to a plane, as can deals with the Devil and other such things.
So that's my reconciliation of the disparate elements of alignment. We have the behavioural aspects determining where the soul resides, and the very fact that the soul has a concrete location gives detection spells and the like something to lock on to. Again, it's more esoteric thinking that will probably have no bearing on my campaign, but it helps me to sleep at night.