Periphyseon, probably completed around 867 AD), Eriugena proposed that the nature of the universe is divisible into four distinct classes:

:1 - that which creates and is not created;
:2 - that which is created and creates;
:3 - that which is created and does not create;
:4 - that which neither is created nor creates. The first stage is God as the ground or origin of all things; the second is the world of Platonic ideals or forms; the