The Nature of Souls

Of course souls exist. I'd have thought that was relatively obvious. If you want proof, look to mummies. Unless you believe the Dukes of Hell take great pains to merely create a facsimile of a person's consciousness that persists, through some dark magic, after that man's body has long since rotted away far beyond the point of functioning? Ask yourself - what would be the point? Oh, no - death is far from the worst thing that can happen to you under their gentle ministrations.
- Rademes Abydos, Archivist of the First Tower
Whilst the society of Theligose is irreligious, it is considered to be common knowledge that each human has a soul - something within them that creates their consciousness, and persists after the death of their body.
Through translation of ancient Infernal records left behind in the surviving cities after 0AR, it was swiftly discovered that the human soul is not in fact indestructible. Countless thousands collected from their subjects were used by their Infernal masters to power their dark magics, and the forces of Hell exhausted practically their entire reserve to resist the human rebellion.
One school of thought holds that the magic utilised by Binders, being Infernal in origin, slowly chips away at their soul, causing older mages to become slowly more callous and uncaring. This is strongly denied by all senior and learned members of the College, with the current Archgoaler being quoted as saying "If I appear unfeeling and cruel, it is because I am either simply those things naturally, or - more likely - you consider me to be so because you have the privilege of surviving whilst being soft and pathetic. You're welcome, by the way."
The eventual fate of the human soul is not known, save that it lies neither with the Heavens nor the Hells. Every attempt to peer beyond the veil of the mortal world has ended in failure. It is possible that mortal magic is simply not capable of divining what lies beyond.
Humanity appears to be unique among sapient creatures in possessing a soul. Animals cannot be "bound" to an undead existence as men can be, and whilst the agents of the upper and lower planes could be argued to have a similarly eternal presence, their essence cannot be separated from their body, and returns to their plane of origin to reform upon their destruction.