Obtainable after beating up Godfrey and unlocking his grace site. It's above you, on the roots. From the grace look toward the big Erdtree to start your root climb.

I think fromsoft literally misscoded Law of Regression it requires only 37 INT to be used not FAITH on a FAITH spell in all souls series before FAITH assiociates with healing and buffs but for some reason the spell wich removes all debuffs/ailments on you requires INT this is a FAITH vendor we talking about pretty sure this is a mistake

In case Corhyn is dead because you have progressed to far into the game, you can still offer the Golden prayerbook to Miriel inside the Church of Vows, and learn Law of Regression .

i gave it to the ****ing turtle because i didnt know where Corhyn was.

from the root that brings you to the second floor, stand on the railing and you can run and jump up to the root where the book is

From the site of grace level, climb the first root up to the 2nd floor. Then go right to outside and then directly left on the roof of the building. There is a broken windows which you can enter to get the Principia

Don't know if this works before Leyndell ... changes ... but to get the book after: go out the door on the second floor, turn left, jump down to the roof, jump into the open window, go around the walkway to where the root ends, walk along the root, pick up item.

You CAN get it at the ashen leyndell.

Does this item remain available once the city has been turned into the capital of ash?