Ab aeterno should be distinguished from in aeternum, which means into eternity or forever into
the future. Ab aeterno looks backward — from before time began — while in aeternum looks forward, into endless future time.
Together they form the two directions of the eternal, the timeless past and the endless future, which between them contain the brief spark of human life. In theological poetry, ab aeterno is associated with divine foreknowledge and predestination; in philosophical verse, it connects to the pre-Socratic concept of the apeiron, the unlimited, from which all things emerge. Students should note that the phrase carries a different weight depending on whether it appears in devotional,
Stoic, or existentialist poetry — in each context the eternal backdrop throws human brevity into a different kind of relief.