From Citizendium, the Citizens' Compendium
Sempiternity (from Latin "sempiternitus": "semper" ["always"] + "aeternus" ["eternal"]) is duration through time without limit; a sempiternal being exists at all times, having "beginningless, endless temporal existence".
In the philosophy of religion and theology, the notion of sempiternity is used in contrast with that of eternity, which is the notion of timelessness; an eternal being is one that exists outside time. The term "eternity" is, however, often used to refer to sempiternity; as Stump and Kretzmann point out, for example: "The many medieval discussions of the possibility that the world is 'eternal' really concern the possibility that it is sempiternal, and most often their concern is only with the possibility that the world had no beginning in time."
Boethius draws the distinction between sempiternity and eternity in his De Trinitate: "For our 'now', as if running, creates time and sempiternity, whereas the Divine 'now' stays not moving, but standing still, and creates eternity".
- Boethius De trinitate in H.F. Stewart, E.K. Rand, and S.J. Tester [transl. & edd] Boethius: The Theological Tractates and The Consolation of Philosophy. Cambridge, MA: Harvard University Press, 1973. ISBN 0674990838
- Thomas V. Morris [ed.] The Concept of God. Oxford: Oxford University Press, 1987. ISBN 0-19-875076-5
- Eleonore Stump and Norman Kretzmann "Eternity". The Journal of Philosophy LXXVIII:8, 1981. References to reprint in Morris .