Edward Feser, Aquinas: A Beginner’s Guide (Oxford: Oneworld, 2009), 107-109.

The idea is that if we start by considering the natures of each of the lower levels of reality and then proceed to follow them upward, we find ourselves inexorably led to a highest level. In particular, degrees of goodness, truth, nobility, and so forth each point beyond themselves to a highest degree of each; since these are all convertible with one another, it is the same one maximum to which they all point; and since they are all in turn convertible with being, this single maximum is also that which is most fully real. What Aquinas is up to in the Fourth Way can therefore be understood when we read the argument in light of his doctrines of the transcendentals, analogy, and the hierarchy of being.

In what sense is this highest level of reality the “cause” of the lower levels? And in what sense do the latter “participate” in the former if it is not in a Platonic sense? The answers to these questions are related. Something “participates'' in a certain perfection when it has that perfection only in a partial or limited way (In DH 2); and for Aquinas, “whatever is found in anything by participation, must be caused in it by that to which it belongs essentially” (ST I.44.1). Unlike Plato, whose emphasis is exclusively on what later thinkers would call formal causality, Aquinas takes there to be an essential link between participating in something and being efficiently caused by it. How so? Consider first the specific case of existence or being, where we have already seen that for Aquinas, “from the fact that a thing has being by participation, it follows that it is caused” (ST I.44.1). The reason for this was that if a thing’s essence and existence are distinct (so that it only “participates” in being or existence rather than being identical with pure being or existence), only something outside the thing could give it existence or being; for to say that its existence derives from its essence (which is the only other alternative) would entail the absurdity that it causes itself. (Keep in mind that deriving or flowing from an essence is not the same as being identical with an essence; for example, the essence of a human being is to be a rational animal, and having the capacity for language flows or derives from this essence, but having the capacity for language flow or derives from this essence, but having the capacity for language is nevertheless not identical with being a rational animal.) We have also seen that, for Aquinas, the cause in question must ultimately be something in which its essence and existence are identical, and which accordingly just is being itself, or (we might nwo say) unparticipated being.

That, of course, is the heart of the “existential proof” and thus (I have suggested) the Second Way, which we have already examined. But given that being is convertible with goodness, truth, and the like, we would expect that what is true of things which have being or existence only by participation will also be true of things having goodness, truth, and so on only by participation, thus opening the way to a distinct argument for God’s existence (namely the Fourth Way). And that is precisely what Aquinas thinks. In particular, he holds that in general (and not just with respect to being or existence) things that have some perfection only to various limited degrees must not have that perfection as part of their essence, “for if each one were of itself competent to have it, there would be no reason why one should have it more than another” (QDP 3.5). That is to say, if it were part of a thing’s very essence to have the perfection, then there would be no reason for it not to possess it in an unlimited way. (Hence any human being is fully human, which follows from being to the fullest extent—which would be possible only for something whose essence just is being—or goodness to the fullest extent—which would be possible only for something in some sense having within it every perfection—and so forth.) So, for a limited thing to have some perfection, it must derive it from something outside it. And as Wippel notes, we would be led into a vicious infinite regress of the sort Aquinas has already criticized unless this something either is or is traceable to a cause which has the perfection to an unlimited degree.

But if the ultimate cause is unlimited in goodness, truth, nobility, or whatever other transcendental we are starting with, then (as we have already said) given the convertibility of the transcendentals it will also have to be unlimited being and therefore just be pure being or existence itself. We are led therefore to the existence of the same being arrived at the end of each of the first three ways—pure act, a being whose essence just is existence in which is the efficient cause of the being or actuality of everything other than itself—via yet another route, a consideration of the degrees of perfection found in the things of our experience.

——————————

Return to Lesson 11: Can One Statement Be More True Than Another? How?