Theism entails that evil is not a positive reality, since all positive reality either is God or is continually sustained in existence by God. Augustine thinks that evil is a privation of good. A privation is more than a lack. Leglessness in a dog is a privation, but in a snake is just a lack. If evil were just a lack, then the problem of evil would be easily solved by the consideration that, of necessity, everything other than God is lacking, since only God is infinite. I want to argue, however, that seeing evil as a privation of good still helps vis-a-vis the problem of evil. This argument continues two earlier posts of mine which discuss an Augustinian theodicy (Part I; Part II).
Imagine two closely related alien species, the flerts and the grents. Both are four-legged, and have basically the same habits. Flerts and grents are solitary and reproduce asexually, never knowing their parents (e.g., the parents produce spores which mature away from them), but the flerts have wings in addition to their four legs and can fly away from predators, while the grents are confined to the ground. Suppose now that Gribby is a normal grent, while Flibby is a flert that, due to a genetic defect, never developed wings.
Winglessness is a lack in Gribby and a privation in Flibby, but unless Gribby and Flibby observe their conspecifics, they are not going to know this. It is not an evil that Gribby is stuck on the ground, but it is an evil that Flibby can't fly. But Gribby and Flibby look and behave in pretty much the same way. They eat the same food, they have to run from predators and cannot fly from them, and so on. They have the same joys and the same pains, and they live pretty much the same lives. All this makes plausible the following:
Claim: Flibby is not worse off than Gribby.
I think this claim is plausible. One might think that Flibby is worse off because he suffers from an evil from which Gribby does not suffer. But "suffers" here is a tendentious choice of word. There is no conscious suffering here, we may suppose. We could imagine that when Flibby is faced with a predator he feels an urge to fly and the inability to fly is painful to him; but we can also suppose--and let us do so--that Flibby also has a second privation, namely that his instincts to fly are missing. Flibby suffers from an evil merely in the sense that he is subject to an evil. But his life is just like Gribby's, and the concrete goods that Gribby's life instantiates are also instantiated by Flibby's life. Another way to see this is to imagine some minor concrete good that Flibby has but Gribby does not. Maybe, Flibby happens to be a slightly better at fishing than Gribby is. Then, if per impossibile we were choosing whether to be Flibby or to be Gribby, we would be very reasonable in choosing to be Flibby. But if Flibby is worse off than Gribby, he is significantly worse off--winglessness is not a minor evil. So if Flibby is worse off than Gribby, it wouldn't be all that reasonable to choose to be Flibby just for some minor concrete good.
Still, it's undeniable that Flibby is subject to an evil, while, as far as the story goes, Gribby is not. We now have two conflicting intuitions: first, that Flibby is no worse off than Gribby, and, second, that Flibby is worse off than Gribby, because Flibby is subject to an evil that Gribby is not subject to. I want to argue that the second intuition is mistaken. For Flibby has a more distinguished nature--by nature he has the dignity of being a winged creature. This good that he possesses, the good of being by nature winged, is a good that Gribby does not have. Because he has this good, he is capable of being subject to an evil that Gribby is not--viz., the evil of being deprived of wings. The additional good outweighs or cancels out the additional evil. Hence, we can consistently say that Flibby is no worse off than Gribby even though Flibby is subject to an evil that Gribby is not.
I want to suggest, now, that if Gribby would have no right to complain to God about being created a grent, likewise Flibby would have no right to complain to God about being created a flert without wings.
Evil is not just a lack but a privation. However, possessing an evil also means one possesses a certain good, namely the dignity of being such as to naturally have the good that the evil deprived one of.
In particular, it follows that while an adult whose intellectual functioning is like that of a child thereby is subject to an evil, the developmentally challenged adult is not thereby less well off than the child. (She may be thereby worse off if she compares herself to others, or if others treat her poorly.)
How far one can take these thoughts in the direction of a theodicy, I do not know.