Uploaded January 2019 | Updated September 2026, 2 hours ago
Here's the formal presentation of the first stage of Edward Feser's Aristotelian proof, from pp. 35-6 of Five Proofs of the Existence of God:
"1. Change is a real feature of the world.
2. But change is the actualization of a potential.
3. So, the actualization of potential is a real feature of the world.
4. No potential can be actualized unless something already actual actualizes it (the principle of causality).
5. So, any change is caused by something already actual.
6. The occurrence of any change C presupposes some thing or substance S which changes.
7. The existence of S at any given moment itself presupposes the concurrent actualization of S’s potential for existence.
8. So, any substance S has at any moment some actualizer A of its existence.
9. A’s own existence at the moment it actualizes S itself presupposes either (a) the concurrent actualization of its own potential for existence or (b) A’s being purely actual.
10. If A’s existence at the moment it actualizes S presupposes the concurrent actualization of its own potential for existence, then there exists a regress of concurrent actualizers that is either infinite or terminates in a purely actual actualizer.
11. But such a regress of concurrent actualizers would constitute a hierarchical causal series, and such a series cannot regress infinitely.
12. So, either A itself is a purely actual actualizer or there is a purely actual actualizer which terminates the regress that begins with the actualization of A.
13. So, the occurrence of C and thus the existence of S at any given moment presupposes the existence of a purely actual actualizer.
14. So, there is a purely actual actualizer."
Also, I probably shouldn't have used "the potential to cause things" as an example of a potential other than the potential for existence, because Thomists are speaking of passive potency when they say "potential." My understanding is, passive potency is an ability to be affected, not to affect things or to cause things. Causal powers are active potencies, which are contrasted with passive potencies (and by extension with potentials).
Here's the formal presentation of the first stage of Edward Feser's Aristotelian proof, from pp. 35-6 of Five Proofs of the Existence of God:
"1. Change is a real feature of the world.
2. But change is the actualization of a potential.
3. So, the actualization of potential is a real feature of the world.
4. No potential can be actualized unless something already actual actualizes it (the principle of causality).
5. So, any change is caused by something already actual.
6. The occurrence of any change C presupposes some thing or substance S which changes.
7. The existence of S at any given moment itself presupposes the concurrent actualization of S’s potential for existence.
8. So, any substance S has at any moment some actualizer A of its existence.
9. A’s own existence at the moment it actualizes S itself presupposes either (a) the concurrent actualization of its own potential for existence or (b) A’s being purely actual.
10. If A’s existence at the moment it actualizes S presupposes the concurrent actualization of its own potential for existence, then there exists a regress of concurrent actualizers that is either infinite or terminates in a purely actual actualizer.
11. But such a regress of concurrent actualizers would constitute a hierarchical causal series, and such a series cannot regress infinitely.
12. So, either A itself is a purely actual actualizer or there is a purely actual actualizer which terminates the regress that begins with the actualization of A.
13. So, the occurrence of C and thus the existence of S at any given moment presupposes the existence of a purely actual actualizer.
14. So, there is a purely actual actualizer."
Also, I probably shouldn't have used "the potential to cause things" as an example of a potential other than the potential for existence, because Thomists are speaking of passive potency when they say "potential." My understanding is, passive potency is an ability to be affected, not to affect things or to cause things. Causal powers are active potencies, which are contrasted with passive potencies (and by extension with potentials).
