» Mon May 14, 2012 7:54 pm
A "Black Soul" isn't a "rank" of soul that's "bigger" than "Grand Souls", so far as I know - a Black Soul just means it's a human soul (I'm not sure if this is the same in Skyrim as it was in Oblivion, but in Oblivion, the humanoid Daedra (like Dremora, Golden Saints and Dark Seducers) were considered "human/black souls", which I never understood).
Anyhow, so far as I know, all human souls are considered "Grand" souls for their "size", Black is just their "type", so to speak. Honestly, I wish soul gems would never store a soul smaller than the size of the gem - always svcks to find out you accidentally stored a lesser or petty soul in a BSG.
The distinction is basically that, in general, you can't soul trap a human soul (in Lore, Arkay protects human souls), but necromancers have been able to figure out how to create Black Soul Gems to defeat Arkay's protection on the human soul.