Affinity tomes contain detailed reports and information father by magi over the years pertaining to a specific affinity. With the exception of the General affinity tome, they will, when read, give you a 10% boost to that specific affinity, while simultaneously reducing your progress in all other affinities.
Affinity Tome: General (also called Affinity Tome: NONE) is a item added by Ars Magica 2. It can be used by the player to reset their Affinities depth back to 0% or unlock their locked Affinity and revert its depth to 0%.