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Aquinas’s Argument for an Uncaused Cause

Published online by Cambridge University Press:  02 May 2025

John R. T. Lamont
John R. T. Lamont*
Affiliation:
Winnipeg, Manitoba, Canada
*
Email: [email protected]
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Abstract

Aquinas presents his argument for the existence of an uncaused cause of all effects in his Second Way in the Summa theologiae as a deductively valid argument from premises known with certainty. This seems unwarranted, since the argument gives no reason for there being only one uncaused cause, and the reasons it gives for rejecting an endless causal regress seem unconvincing. These apparent shortcomings can be better understood by examining Aquinas’s metaphysics of causation, which is presupposed by the argument. He uses a form of composition argument to justify the claim that endless per se causal series cannot exist. He does not argue against the possibility of a multiplicity of uncaused causes because he sees no rational grounds for entertaining this possibility. Given Aquinas’s metaphysical assumptions, it is correct to take the Second Way to be a deductively sound argument.

Keywords

AquinascauseeffectGodSecond Way
Type
Article
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New Blackfriars , First View , pp. 1 - 18
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Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Provincial Council of the English Province of the Order of Preachers.

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References

1 Standard versions of abbreviations for Aquinas’s works are used here; a glossary for them is provided below.

2 St. Thomas Aquinas, Commentary on the Nicomachean Ethics, vol. 1, tr. C. I. Litzinger (Chicago: Regnery, 1964), pp. 2–3. Latin texts in this article are taken from www.corpusthomisticum.org. Where not otherwise indicated, translations from Latin are my own.

3 St. Thomas Aquinas, On the Truth of the Catholic Faith: Summa contra Gentiles, Book One: God, tr. Anton C. Pegis (New York: Doubleday, 1955), p. 119.

4 See e.g. Joseph Bobik, Aquinas On Being and Essence (South Bend: University of Notre Dame Press, 1965); John Wippel, ‘Aquinas’s Route to the Real Distinction’, The Thomist 43 (1979), pp. 279–9; Joseph Owens, Aquinas on Being and Thing (Niagara Falls, NY: Niagara University Press, 1981); Lawrence Dewan O.P., ‘Saint Thomas, Joseph Owens, and the Real Distinction between Essence and Existence’, Modern Schoolman 61/3 (1984), pp. 145–156; Gaven Kerr, Aquinas’s Way to God: The Proof in De Ente et Essentia (Oxford: OUP, 2015).

5 See John Wippel, ‘Thomas Aquinas on Creatures as Causes of Esse’, International Philosophical Quarterly 50 (June 2000), pp. 197–213; the main text here is De potentia q. 5 a. 1.

6 See Plotinus, Enneads 5:4.1.5–15, 5:9, 6:8-9, and Lloyd P. Gerson, Plotinus (London: Routledge, 1994), pp. 3–35.

7 For Aquinas’s nuanced view on the temporal relation between cause and effect, see William A. Wallace, ‘Aquinas on the Temporal Relation Between Cause and Effect’, The Review of Metaphysics 27/3 (1974), pp. 570–584.

8 St. Thomas Aquinas, On the Truth of the Catholic Faith, Book Three, Part One: Providence, tr, Vernon J. Bourke (New York: Doubleday, 1956), p. 236.

9 Aquinas’s reference to causing motion upwards or downwards assumes that material bodies have a tendency resulting from their essence to move to their natural place, a tendency which produces upward or downward motion; cf. De caelo et mundo lectio 18 n.175. See Daniel Shields, ‘Everything in Motion is Put in Motion by Another’, American Catholic Philosophical Quarterly 92/4 (2018), pp. 535–561, on Aquinas on motion.

10 See, e.g. William Rowe, The Cosmological Argument (Princeton: Princeton University Press, 1975), pp. 19–20; Joseph Owens, ‘Aquinas and the Five Ways’, The Monist 58/1 (1974), pp. 24–25.

11 Peter Geach, ‘Aquinas’, in G. E. M. Anscombe and P. T. Geach, Three Philosophers (Oxford: Basil Blackwell, 1961), pp. 113–114.

12 On composition arguments see William Rowe, ‘The Fallacy of Composition’, Mind 71 (1962), pp. 87–92; D. N. Walton and J. Woods, ‘Composition and division’, Studia Logica 36 (1977), pp. 381–406; Maurice A. Finocchiaro, ‘The fallacy of composition: Guiding concepts, historical cases, and research problems’, Journal of Applied Logic 13/2, June (2015), Part B, pp. 24–43.

13 Caleb Cohoe, ‘There Must Be a First: Why Thomas Aquinas Rejects Infinite, Essentially Ordered, Causal Series’, British Journal for the History of Philosophy 21/5 (2013), pp. 838–856.

14 See, e.g. Richard Cartwright, ‘The Second Way’, Medieval Philosophy and Theology 5 (1996), pp. 189–204.