User blog comment:IamJakuhoRaikoben/Chapter 360: The White Inheritance, Review./@comment-4489126-20131115224855/@comment-7418318-20131116085211

It might even be that this is how Human Subordination and Celestial Spirit Magic were created, by modifying those basic theories invented/found by Zeref... or maybe the other way round an Zeref got inspired by CSM.