The First Cause argument holds that the chain of causes operating in the world cannot extend backward without limit, and therefore must terminate in a first cause that is itself uncaused. From the observation that every effect has a cause, the argument infers the existence of an originating cause that grounds the entire causal order without itself requiring an external explanation.
The argument has classical roots in Aristotle's Physics and Metaphysics, where the Prime Mover serves as the ultimate source of motion. It was developed in early Islamic philosophy by al-Kindī, who fused Aristotelian causation with the theological doctrine of the createdness of the world. Aquinas presented a version as the Second Way in the Summa Theologiae, distinguishing essentially ordered causal series (which cannot proceed to infinity) from accidentally ordered ones (which arguably can). The contemporary scholastic revival, notably in Edward Feser, has restated the argument in modern analytic terms, emphasizing that the impossibility of infinite regress applies to per se causal chains where each member depends in the present moment on the prior member's causal activity.
Critics from David Hume onward have questioned the premise that every event must have a cause, particularly when extended from observed regularities to the universe as a whole. Bertrand Russell famously argued that the universe might simply be a "brute fact" requiring no further explanation. Contemporary critics such as Graham Oppy have challenged the distinction between per se and per accidens causal series, and the claim that the first cause must have the attributes traditionally ascribed to God.
Among other formulations in the cosmological family, the First Cause argument differs from the Kalam version in not requiring a temporal beginning of the universe — it concerns causal dependence rather than temporal origination. It differs from the Contingency Argument in operating with the notion of cause rather than the modal notion of contingency and necessity. It differs from Ibn Sīnā's proof of the truthful (burhān al-ṣiddīqīn) by reasoning from effects rather than directly from the nature of existence itself.