Stephen Law’s argument that no theists have ever argued for the infinite goodness of God is understandable – why should he be expected to know the Fourth Way, which concludes that there must be some infinite good (that is, a good not limited by a subject)? The Fourth Way can be stated as a simple consequence: we sense and experience that some things are more or less good, therefore there is some Absolute and unlimited summum bonum. The argument can be interpreted in more than one way. Here are some possible explanations:
1.) If the absolute and unlimited good had only a potential existence, then it could not be the limit of the actual goods that are more or less good. Potential limits do not limit actual things.
2.) Because there really is a more and less, what is maximally and absolutely good is possible. But for X to be possible requires either that X exists or something is capable of making it. It follows either that there is some absolute and maximal good, or a being that has all that is necessary within himself to give rise to one. Either way, there is some absolute and maximal good.
3.) What is said of things is said most of all of that which it is said of first and per se, that is, first and by its very nature. But every investigation into a thing seeks that which the thing belongs to per se and first. Thus, because it is impossible to investigate what good is, there is some absolute and maximal good.
And some suggestive approaches:
4.) If the human will loved the finite good, it would have to love it as finite. But good cannot be loved in its termination and the finite limit terminates the good. In loving the good, we love it first of all as infinite, and find it repugnant as finite.
5.) The will seeks what is absolutely good by its nature. But natural desires are formed and actualized by an environment in which their objects can be found. The will thus finds God in a kind of environment in which it lives.