Aseity

The word comes from the Latin a se, "from itself," and contrasts with ab alio, "from another." For classical theists, every creature exists ab alio — derivatively, dependent on God for its continued existence. God alone exists a se, in virtue of what he is. Thomas Aquinas treated aseity as one of the divine attributes that follow from God's simplicity and perfection, and it has been central to philosophical theology in the Abrahamic traditions ever since.

Aseity is closely tied to the cosmological argument. The standard classical move is to argue that the chain of contingent dependent beings cannot regress forever, so there must be a being that exists non-derivatively — a being whose essence just is existence, whose non-existence is impossible. That being is God, and the property that makes God the terminus of the regress is aseity.

The position is elegant but it generates its own problems. A being that exists purely from itself, whose existence is identical with its essence, is hard to distinguish from a brute fact. What we wanted was an explanation for why anything exists, and the answer "there is a being whose existence needs no explanation" looks suspiciously like giving up on the question with a metaphysical flourish. Critics sometimes press this as the "necessary being" problem: invoking aseity is a way of stopping the regress, not explaining it.

For a secular reader, aseity is worth understanding because it names a specific move that classical apologetics relies on heavily. When a theist argues that "something must have existed necessarily," the concept they are reaching for is aseity. Knowing the term lets you ask the right follow-up — why should we believe any being has that property, and what work does calling a brute fact "self-existent" actually do?