The measure of beings that are mutable but not subject to material conditions, i.e., the angels as well as separated and resurrected souls, as regards their created acts “outside” of the vision of God.  Aeviternity measures instantaneous acts of knowing and willing which are not subject to the conditions befalling motion, due to motion’s imperfection as act.  Aeviternity is an analogate in the larger analogical set that is duration, which also includes time and eternity.