As part of the Soldiers of Fortune upgrade, the system of unit enhancements known as Doctrines has been massively expanded.
Previously, all Doctrines were semi-randomly issued by the War Scholar in return for a Treatise, which could then be applied to a unit as a permanent boost to one of its attributes.
In addition, you can now acquire Seasonal Doctrines. These have the potential to be more impactful than regular doctrines, at a cost to the fact that they’re limited to specific units rather than unit types, and that they only remain active for a short time (from 1 to 12 days after being activated).To illustrate this distinction there are now Epic and Legendary Doctrines.
A small selection of Seasonal Doctrines can currently be bought from the Seasonal Store (F5) for a small amount of Barbutes, with others issued as rewards for capturing fiefs and acquiring new titles.
Seasonal Doctrines cannot be salvaged and will expire at the end of the current season, regardless of whether they’re in active use or not. Otherwise, they are like regular Doctrines in that they cannot be reassigned to another unit.