Philosophy / Natural Theology • Existence of God • Advanced
Thomistic First Cause Argument
Primary question: Does the existence of dependent, caused things require an uncaused first cause that sustains them?
Argument map
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Common mistakes
Don't say
Treating this as an argument about what caused the Big Bang or the temporal beginning of the universe.
Instead
Recognize it concerns what sustains existing things in being right now, a hierarchical rather than temporal regress.
Don't say
Assuming 'first cause' means first in a countable series of past events.
Instead
Understand 'first' as metaphysically first or underived, not first in a timeline.
Don't say
Thinking the argument alone proves the God of a specific religion.
Instead
See it as establishing a metaphysically first cause of being, with further argument needed to attribute personal or specifically theistic attributes.
What would change my mind? — Christian position
A rigorous demonstration that infinite essentially ordered regresses are metaphysically coherent and explanatorily sufficient would remove the argument's force, though it would not by itself disprove God.
What would change my mind? — Skeptical position
A compelling account of why derivative causal power can be explained by an endless regress, or a workable alternative metaphysics without act/potency, would be needed to overturn the argument on its own terms.
Why does this matter?
This argument matters because it represents one of the most historically influential and philosophically rigorous attempts to move from everyday causal dependency to a transcendent sustaining cause. It shaped centuries of Christian, Jewish, and Islamic philosophical theology, and continues to be defended and contested by professional philosophers, making it a central test case for whether classical metaphysics can do real argumentative work today.
For further study
Primary and secondary sources on both sides of this question. Reading the strongest opposing case is part of the work, not a concession.
Summa Theologiae, I, q.2, a.3 — Thomas Aquinas
The original text of the Five Ways, including the Second Way.
Aquinas: A Beginner's Guide — Edward Feser
Accessible modern exposition and defense of the Thomistic arguments.
Aquinas on Mind — Anthony Kenny
A critical philosophical assessment, including objections to the causal premises.
The Miracle of Theism — J.L. Mackie
Contains an influential critique of cosmological arguments including the regress premise.
Being and Some Philosophers — Etienne Gilson
Classic Thomist treatment of existential metaphysics underlying the argument.