The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But “more” and “less” are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, …Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.New Advent; Summa Theologica
This is an argument for God’s existence that I imagine might get some flack by modern readers. For one thing, we define the Kelvin temperature scale based on absolute zero, e.g. what is coldest not what is hottest. The statement that fire causes all heat might also raise modern eyebrows. The argument is right though that any objective scale needs an objective reference point. This is why Kelvin is a good scale, absolute zero serves as an objective reference point.
That being said, there are gradations of goodness observable. Animals are more valuable than rocks. a baby outclasses a worm. What standard are we using to discern what is good?
Pure evil can’t be used as a reference point. Pure evil is not possible as evil is defined as a lack of goodness. There has to be some goodness for something to go bad. A human being’s bad actions are bad precisely because of the goodness that was possible for that being.
Furthermore, defining a standard of goodness on pure evil would create a bleak outlook on life.
Picking a finitely good thing to serve as a standard of goodness is also a problem because any choice would be arbitrary. Furthermore, finite creatures do not cause their own existence, and thus finite things are not the first cause of their own goodness either. What gives them their goodness would always be a stronger standard of the good.
Thus the argument’s conclusion is still logical: When we recognize things are more than less good, we are implicitly implying an existence of goodness itself or of being itself. This ipsum esse subsistens is God. As pure being it would be able to sustain its own existence and, like fire giving heat, give being and goodness to creatures.
See Peter Kreeft’s take, here.