I would call a soul the essence of who we truly are. All of our thoughts, our personality, our hopes and dreams... all of it. A body without a soul is dead, of course... Though I've seen plenty of undead, zombies and so forth, roaming around soullessly. Not a pretty sight.

[It's something Kain has thought about a great deal. He's seen too much back home not to understand the difference, the way that the undead aren't really themselves. There's a look in the eyes that somehow shows whether that soul is in there or not. He's also experienced death and being in soul-form himself, though that's not something to bring up at the moment.]

Your spirits here seem very different than that. They normally don't have mortal bodies of their own, for one thing, do they?