A key part of Aquinas’ argument for the existence of God in Summa Theologica is found in Question 14, Article 1: “Whether There Is Knowledge in God?”.  In that article, Aquinas argues for the conclusion that “In God there exists the most perfect knowledge.”  The word “God” here is a misleading translation, and I take this claim to mean the following:

(MPK) In the first principle there exists the most perfect knowledge.

Aquinas provides only ONE argument for this conclusion (at least in Summa Theologica), and this conclusion is essential to Aquinas’ argument for the existence of God, so if that ONE argument fails, then Aquinas’ argument for the existence of God (in Summa Theologica) also fails.

NOTE: Aquinas might have other arguments for the existence of God in other writings; I’m only concerned here about his argument for God in Summa Theologica.

This conclusion (MPK) is critical to the success of Aquinas’ argument for the existence of God, because it is the basis on which Aquinas argues for three key divine attributes:

(AKB) The first principle is an all-knowing being. 

(see Question 14, Articles 2 through 6)

(PLB) The first principle is a perfectly-loving being.

(see Question 20, Articles 1 through 4, and Question 19, Article 1)

(PJB) The first principle is a perfectly-just being.

(see Question 21, Article 1, and Question 19, Article 1).

Thus, if Aquinas fails to prove (MPK), then he also fails to prove that the first principle is all knowing, and fails to prove that it is perfectly loving, and fails to prove that it is perfectly just.  If Aquinas fails to prove that these divine attributes apply to the first principle, then he fails to prove that God exists, because these are basic and essential divine attributes.  If Aquinas cannot show that these divine attributes apply to the first principle, then he cannot show that the first principle is God (in the ordinary sense of the word “God”), and thus cannot show that God exists.

Aquinas’ ONE argument for (MPK) concludes with these words (from Question 14, Article 1):

Since therefore God is in the highest degree of immateriality, as stated above (Q. VII, A. I), it follows that He occupies the highest place in knowledge.

This means that the ONE argument that Aquinas gives for (MPK) is based on the following assumption (because the word “God” is a misleading traslation here, I have rephrased the premise using a more generic term):

(HDI)  The first principle is in the highest degree of immateriality.

Aquinas indicates that (HDI) is argued for in Question 7, Article 1.  But Question 7, Article 1 is specifically about “Whether God Is Infinite?”.   The conclusion of that article is that “God is infinite.”  The word “God” is a misleading translation here, and I take this conclusion to mean this:

(FPI) The first principle is infinite.

Again Aquinas gives only ONE argument for the conclusion (FPI).  Presumably, Aquinas believes that (FPI) implies (HDI), or that (FPI) can be used as a premise in an argument for (HDI), making the conclusion of Question 7, Article 1 relevant to the assumption (HDI), which he needs in order to prove the key claim (MPK).

The ONE argument given by Aquinas for (FPI) concludes with these words (from Question 7, Article 1):

Since therefore the divine being is not a being received in anything, but He is His own subsistent being as was shown above (Q. III, A. 4), it is clear that God Himself is infinite and perfect.

The word “God” here is misleading; the phrase “the divine being” is better, but to be consistent with how the other key claims have been phrased I take this premise to mean this:

(OSB)  The first principle is its own sufficient being.

Here is the logical structure of the core argument within the overall structure of Aquinas’ argument for the existence of God (in Summa Theologica):

(OSB)–>(FPI)–>(HDI)–>(MPK)

If Aquinas fails to prove (OSB), then Aquinas fails to prove (MPK), and if Aquinas fails to prove (MPK), then Aquinas fails to prove the existence of God, because (MPK) is needed to establish that the first principle has three key divine attributes (i.e. is all knowing, perfectly loving, and perfectly just).

Furthermore, if any of the inferences here are mistaken or illogical, then Aquinas fails to prove (MPK), and thus fails to prove the existence of God (note that additional premises are often stated and required).  Therefore, this chain of reasoning is essential to Aquinas’ argument for the existence of God as given in Summa Theologica.

In the passage quoted above, Aquinas indicates that (OSB) is proven in Question 3, Article 4:  “Whether Essence and Being Are the Same in God?”.  In this article, Aquinas gives THREE arguments in support of (OSB).

The first argument connects back to the 2nd of the Five Ways.  Here is a key part of this first argument (from Question 3, Article 4):

Therefore that thing whose being differs from its essence must have its being caused caused by another.  But this cannot be said of God, because we call God the first efficient cause.  Therefore it is impossible that in God His being should differ from His essence.

The word “God” is a misleading translation, so I take the key premise here to mean this:

(FEC)  The first principle is the first efficient cause.

So, (FEC) is a key premise in an argument that Aquinas offers to prove (OSB):

(FEC)–>(OSB)

The second argument for (OSB) ends this way (from Question 3, Article 4):

Therefore, since in God there is no potentiality, as shown above (A. I), it follows that in Him essence does not differ from His being.  Therefore His essence is His being.

The word “God” is a misleading translation; I understand the key premise here this way:

(HNP) The first principle has no potentiality.

So, Aquinas uses (HNP) as a premise in an argument to prove (OSB):

(HNP)–>(OSB)

The third argument for (OSB) concludes this way (from Question 3, Article 4):

But God is His own essence, as shown above (A. 3); if, therefore, He is not His own being He will be not essential, but participated being.  He will not therefore be the first being–which is absurd.  Therefore God is His own being, and not merely his own essence.

A key premise in this argument is that “God is His own essence”.  The word “God” is a misleading translation, so I take this premise to mean this:

(IOE)  The first principle is its own essence.

Aquinas takes (IOE) to be a key premise in an argument to prove (OSB):

(IOE)–>(OSB)

Now we can take the core argument in Aquinas’ overall argument for the existence of God and add the three main conclusions on the back end, and add the three main reasons/premises for (OSB) on the front end (click on the image below to get a clearer view of the chart):

1. This entire chain of reasoning exists OUTSIDE of the Five Ways passage (which is found in Question 2, Article 3).

2. This chain of reasoning is ESSENTIAL to Aquinas’ argument for the existence of God in Summa Theologica. (If this chain of reasoning fails, then Aquinas’ argument for the existence of God in Summa Theologica fails.)

THEREFORE:

3. The Five Ways passage does NOT contain any proof of the existence of God (not even just one proof).

Furthermore, although there are three separate arguments given in support of (OSB), there is only ONE chain of reasoning from (OSB) to the key claim (MPK), and there is only ONE chain of reasoning from (MPK) to the conclusion that God exists, namely to arrive at the conjunction of  (AKB), (PLB), and (PJB), plus a few other key divine attributes.  Thus, although one could technically construct three different proofs based on the structure of the logic shown in the chart above, the reasoning in those three proofs would be identical starting from the point at which one concludes that (OSB) is the case.

That is to say, about 80% of the proof or chain of reasoning would be identical between the “three proofs”.  The only difference between the proofs would be how one initially proves or argues for the key claim (OSB).  It seems more reasonable to me to say that there is just ONE argument for the existence of God in Summa Theologica, but that a key premise of that argument is supported by three different sub-arguments.  It would certainly be very misleading to assert that “There are three separate and distinct arguments for the existence of God in Summa Theologica.”

So, I still hold the view that there are ZERO proofs of the existence of God in the Five Ways passage, and that there is just ONE argument for the existence of God in Summa Theologica.