This artikel has a few theories about certain parts of the books:
Theory 1.
To get the Remnant out of Tanith all we need to do is-
1. Force her into Dr Nye's old lab as that casues people to die but remain conscious
2. Get Dr Nye to use its research into the soul and pull the Remnant away from Tanith's soul
3. If that doesn't work, just put Tanith at peace
Theory 2.
Argeddion's magic before finding his True Name is unknown, but I have an idea. It's Sensitive, I think this because-
1. It explains why he was able to control people's minds
2. It would explain how he could read minds
Theory 3.
You know...