Many misunderstandings about the Fourth Way can be resolved if we take the words of the proof very seriously.
The fourth way is taken from the gradations that are found in things.
The proof is based on gradations found in things. Our focus on the “gradations” cannot distract us from the things in which we find them. One man might be more or less musical, but “musical” is not the same thing as “a man”; one rose might be more or less beautiful, but beauty is not the same thing as a rose. The proof therefore starts with a discussion of composites of a form in a subject, or generally of composites of act and potency. If you don’t understand this sort of composition, stop reading the proof immediately, or at least don’t claim to understand what follows.
For there is found in things a more and less good, true, noble, and other such like things.
St. Thomas is restricting the notion of composition to the composition of good with a good thing; truth with a true thing; nobility with a noble person, and other such like compositions. Given this restriction, we either have to
a.) State exactly the class of things that St. Thomas is speaking of, and then speak only of that class of things as such, or
b.) Explicitly limit ourselves to a discussion of good, true, noble, and heat, which are the only “such like” things that St. Thomas mentions.
The first option is difficult. St. Thomas seems to have in mind positive qualities (in the broad sense of quality, not the one limited to a genus) which are limited by the subjects in which the qualities are found. St. Thomas’s example of “heat ” is perfectly chosen here, because the limit of how hot something can be is the combustion point or flash point of the thing in which the heat is. Wood can’t keep getting hotter forever- at some point it bursts into flame. The same is true of paper and other flammable things. So too with goodness- one man might become more or less good, but his human nature places a limit on how good he can become.
More generally, the class of things the Fourth Way speaks of is act so far as it is limited by potency. We need to be even more restrictive than this, however, for by the very nature of what St. Thomas is doing here he is limiting himself to a consideration of the qualities which belong to the meaning of the term “God”: goodness, truth, wisdom, love, justice, power, etc. If St. Thomas were not implicitly making this restriction, he would not be proving the existence of God. The example of heat has a likeness to these things, but it is not formally what the proof is considering, since the word “God” doesn’t mean the being with the greatest amount of heat.
The first and the second premise, if put very generally and abstractly (which makes it dreadfully clunky and devoid of its original thomistic simplicity and grandeur), would read like so:
The fourth way is taken from the degrees of act that we find in subjects or potencies. For subjects have more or less of some actuality in such a way that the subject is a limit of the act. Among such composites, some have an act that is a part of the meaning of the term “God”. This is especially the case with goodness, truth, nobility, and other such like things- like wisdom and power, for all who speak of God (whether they know him or not) speak of some intelligent, good, lofty, powerful being.
St. Thomas continues:
But more and less in diverse things is said according to the diverse ways in which they approach toward something (ad aliquid) that is most.
The bolded section is the one which causes the most difficulties when overlooked. St. Thomas is saying that there are many ways of approaching toward some maximum. At this point in the proof, we are free to think that the maximum might be reached in some cases, in others not; the maximum might exist actually in some cases, in others not; the maximum might be the term of a finite series in some cases, in others not. In some cases, the maximum is simply contradictory (This is the case with privations. No evil can be such that it wholly eliminates the good of the subject.)
If I only had a nickel for every time that someone objected to the Fourth Way by saying that there is more than one way of approaching toward some maximum! “St. Thomas is wrong here, sometimes the maximum is impossible, contradictory, at an infinite distance, only possible, etc. This is not even an objection, but an integral part of the Fourth Way! Of course there are many ways of approaching toward a maximum. You might cite St. Thomas as an authority to the opinion.
Est igitur aliquid quod est verissimum, et optimum, et nobilissimum, et per consequens maxime ens, nam quae sunt maxime vera, sunt maxime entia, ut dicitur II Metaphys
There is therefore something that is most true, best, and loftiest, and as a consequence [is] most of all existent, for the things that are most of all true are most of all existent, as is said in II Metaphysics.
There is something most true in one way or another. But Metaphysics Book II tells us that as something is true, so it exists, (or “has ens“, but St. Thomas is pretty clear that “ens” is taken from the act of essence, and this act is existence). I’m often amused by the Fourth Way being called “the most Platonic” of the proofs, when in fact its central middle term is taken from the second book of Aristotle’s Metaphysics. Without this argument that draws a bond between truth and existence, we only know that what is more an less true approaches some most, not that some most true being actually exists.
But if St. Thomas has shown that God exists, why does he not say so? Why does the proof keep going? There are three reasons:
1.) St. Thomas does not so much look at the existence of “ens” as he looks at its universality. The fourth Way will conclude to God as absolutely over all being as such.
2.) St. Thomas does not want to see God as a “being” but as the source of being. There is no flatland of being that is shared between God and creatures.
3.) As St. Thomas proves in the article previous to the Five Ways, we come to God through his causality of creatures, and so St. Thomas must invoke causality explicitly in his proof, which he has not done yet.