Here is my problem with the fourth way.
We see things that are “better” and “worse”, and it is usually argued that therefore we need a standard - an ultimate good, and (if we would be consistent) an ultimate bad (unless we say that bad is simply the absence of good - which certainly isn’t linguistically correct, at any rate). Yet all we have actually shown is that we are in fact using a concept of “good” and a concept of “bad” univocally to apply to different degrees of perfection. This concept of “good” necessitates neither an infinite perfection which we simply see “less” of in the created world, nor a separate personal being called God. God is something very different from the meaning of the word “good” we find in the dictionary. “Good” is an adjective referring to finite things, while God is the Trinitarian deity who created heaven and earth.
So the Fourth Way proves only a univocal meaning for the term “goodness”. What I have yet to see is an argument that goes from this to God.
To take an analogy, we see more or less mass in objects and particles, but this by no means indicates that there is an infinite mass somewhere in the universe.
Likewise, seeing degrees of temperature does not mean there is a reservoir of infinite heat somewhere (in fact, the amount of energy in the universe is finite).
I think there are a couple of arguments that move from the degrees of goodness or perfection to the existence of an ultimate good. First, the ideas of better/worse are universal in human experience. This places the hierarchy of those values as part of human nature. The concept of better/worse is found everywhere and always has been among all classes and ranks and eras of humanity.
Along with that, the nature of better/worse judgement is a reference point. One does not need to compare the mass of particles with each other since particles themselves (and anything in the universe including intellectual concepts) can be compared with the concept of uttermost-good or perfection. We compare anything and can see how it could be better. Again, better/worse is judged in relation to an object and a purpose. A large particle is better than a small one for some reason. But in comparison to perfection itself, particles of any mass are limited. They cannot do every possible good thing, they do not possses every power and they do not possess the fullness of being. So those limits are flaws and defects versus the perfection of everything.
So, there is a universal reference point that all human beings understand (since everything can be judged against that reference). By inference, we notice that no human being has ever seen the perfect/ultimate good, and yet, every human being possesses the concept of the final end of the hierarchy of good since we can compare against it.
If there wasn’t truly a perfect or supreme being at the end of the gradation, we would never know that there were degrees of perfection – some closer to the end and some farther. This is very similar to the argument of being – we know that being exists since we all possess it. A supreme being must exist in order to give existence to all contingent beings. In the same way, perfection must exist to be the fixed standard by which we measure good (or to know that there is a measure).
This is similar to the arguments against an infinite regress also. In an infinite string, one cannot measure the distance to the end or the beginning because there is no end or beginning. There can be no scale of gradation of progress towards the end because in order to measure distance to the end, there needs to be an end.
The same is true of perfection. In order to measure distance towards the fullness of perfection it has to exist - otherwise we would not be able to measure if something was better/worse in comparison with perfection. There would be no possible end-point and thus no scale of degrees towards the end.
We know that better/worse exist. There must be an ultimate, highest point on the scale to allow for the existence of the concepts of better/worse themselves. Without the existence of a perfect, supreme good, the concepts of better/worse themselves could not exist (since better/worse are always pointing to a scale of perfection and the scale can only exist if an endpoint exists).