An Appraisal of Aquinas’ First Way: Formalization (Part 2)

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In Part 1 of this series, we introduced Aquinas’ argument from motion and provided some textual exegesis. Given the aforementioned exegesis and explanation, Aquinas’ argument from change can be formalized as follows:

P1: Some things change (i.e. there are changes).

P2: But change is the reduction of potential to actual (i.e. the actualization of potential).

P3 (P1, P2): Therefore, some things reduce from potential to actual.

P4: Whatever reduces from potential to actual is actualized by some other actually existent thing.

P5 (P3, P4): Therefore, some things are actualized by some other actually existent things.

P6: If some things are actualized by some other actually existent things, then there are chains of changes (i.e. one thing changed by another, in turn changed by another, and so on).

P7 (P5, P6): Therefore, there are chains of changes.

P8: If chains of changes were infinitely long, then there would be no first member in the series of changes.

P9: But if there were no first member in the series of changes, there would be no subsequent changes.

P10: But if some things change, then there are subsequent changes.

P11 (P1, P10): Therefore, there are subsequent changes.

P12 (P8, P9, P11): Therefore, it is not the case that chains of changes are infinitely long.

P13: If it is not the case that chains of changes are infinitely long, then such chains terminate in one first member (the unchanged changer or unactualized actualizer).

P14: If such chains terminate in one first member (the unchanged changer or unactualized actualizer), then God exists.

P15 (P12, P13, P14): Therefore, God exists.

Although Aquinas did not, of course, make every such step explicit in his presentation of the argument, all are either implicit in what he writes or are relatively unobjectionable fillers that are necessary for the argument’s validity. The formalized version of Aquinas’ argument, as stated above, is valid. P3 follows by substitution, with the premises in parenthesis as the sub-premises. P5 follows by universal instantiation. P7 and P11 follow by modus ponens. P12 follows by transitivity and modus tollens, and P15 follows by transitivity and modus ponens. It remains to be seen, however, whether the argument is sound. It is to this question that I shall turn in the next part of the series.

Author: Joe

Email: NaturalisticallyInclined@gmail.com

10 thoughts on “An Appraisal of Aquinas’ First Way: Formalization (Part 2)

  1. Pingback: An Appraisal of Aquinas’ First Way: Externalism Contra Act and Potency? (Part 3) – Majesty of Reason

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  8. Thank you so much for this thoughtful analysis. The main problem I see with Aquinas’ argument, as revealed by the way you unpacked it, is in the following premises:

    P8: If chains of changes were infinitely long, then there would be no first member in the series of changes.

    P9: But if there were no first member in the series of changes, there would be no subsequent changes.

    These together reduce to: If chains of changes were infinitely long, there would be no subsequent changes.

    I don’t see why this is the case. For every change, you can cite a previous change which caused it, and a prior change before that which caused it, ad infinitum. I see no logical problem with the idea of an infinite regress of causes.

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    • Thanks for the lovely comment! So, a quick clarification: I’m not a Spinozist. I just like Spinoza’s quote about the majesty of reason 🙂

      So, with that being said, I don’t commit to there being one thing in existence. And so my views allow for multiple abstracta. (I’m not exactly 100% sold on realism, but I very tentatively lean towards it; and I think, very tentatively again, that a kind of contemporary analytic platonic realism is one of more plausible versions of realism.)

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  9. Both Paul Edwards (see his article, The Cosmological Argument, reprinted in Critiques of God, Ed. Peter Angeles) and William Rowe (see his book, The Cosmological Argument) have offered powerful critiques of this argument. In particular, its conclusion that infinite chains of causes are impossible is fallacious and based on circular reasoning (P8 and P9).

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