Modality of being that exists by itself (a se) and not by another.
Following Scholasticism, this term expresses especially the independence of God, who exists from himself a se; or by himself per se, so that we can say in the same sense perseity.
More particularly
From the Scholastic Latin aseitas, derived from a se (“from itself”), aseity designates the mode of being that exists by itself, not through another. It expresses the absolute independence of the First Being, whose essence and existence are one and who depends on no external cause.
In Scholastic theology, the term applies uniquely to God, the only being whose essence entails existence. To say that God exists a se or per se means that He is the source of His own being: uncreated, uncaused, and the principle of all that is. Aseity thus marks the metaphysical distinction between the Necessary Being, which cannot not exist, and contingent beings, which exist only through participation in the first cause.
In the metaphysics of Pure Act, aseity identifies God as ipsum esse subsistens—“Being itself subsisting”—a formulation of St. Thomas Aquinas. Aseity here is not a self-enclosed autonomy but the plenitude of Being from which all things derive and in which they share. It expresses both the ontological autonomy of the Principle and its creative fecundity.
In modern philosophy, several thinkers revisited this notion. For Descartes, God is the one whose existence is necessary; for Spinoza, Deus sive Natura is causa sui, the cause of itself, implying its own existence by necessity; for Leibniz, aseity underlies the principle of sufficient reason. Yet classical metaphysics preserves a decisive difference: God is not an impersonal substance but the living and conscious source of all being.
Spiritually, to acknowledge divine aseity is to recognize that created existence is essentially relational—it is only by participation in the One who exists by Himself that anything exists at all. Aseity thus names the metaphysical absolute: the unconditioned Source from which all things proceed and to which they ultimately return.
Further reading:
– St. Thomas Aquinas, Summa Theologica, I, q.3 & q.44 – on God as ipsum esse subsistens.
– St. Anselm, Proslogion, II–IV – on “that than which nothing greater can be conceived.”
– John Duns Scotus, Ordinatio, I, d.2 – early distinctions between aseitas and causa sui.
– René Descartes, Meditations on First Philosophy, III – on the idea of a being whose existence is necessary.
– Baruch Spinoza, Ethics, I – on substance as causa sui.
– Étienne Gilson, Being and Some Philosophers / L’Être et l’essence.
– Bruno Bérard, Metaphysics for Everyone (Angelico Press), trad. of Métaphysique pour tous (Paris, L’Harmattan, 2021); It. Sui sentieri della metafisica; Sp. ¿Qué es la metafísica?; Ger. Was ist Metaphysik? – on aseity as the metaphysical expression of the Absolute and the ground of all ontological participation.