In his argument that, for Aquinas, it is divine power that make statements about possibility true, Brian Leftow (“Power, Possibilia, and Non-Contradiction,” The Modern Schoolman 82 [May 2005]) obliquely addresses a question that I have been pondering recently: is evil “possible”? The question is prompted by Aquinas’s theocentric theory of the possible: what determines the nature of possibility is the divine being itself, such that a thing is possible on account of its being capable of bearing some creaturely likeness to the divine essence. In short, possibility is divine imitability. To this understanding Leftow’s thesis adds the further, distinctive claim that because God’s essence is identical with his power, for Aquinas it is therefore the case that God’s power is what makes claims about possibility true. As I have argued elsewhere, because God’s power is also his justice and wisdom, divine attributes which Aquinas characterizes, in part, in such aesthetic terms as proportionality and order, there is also sense for Aquinas in which the possible is none other than the beautiful. (I think a consideration of divine goodness, justice, wisdom, and—finally—beauty gets one further in understanding the nature of possibility than a mere consideration of divine power allows, a limitation that Leftow’s discussion unwittingly testifies to.)
If the possible is determined by the divine essence, goodness, wisdom, and justice, however, this raises the question as to in what sense evil, as the contradiction of all of these attributes, is in any way “possible.” (Note that this is not to be confused with the question of whether evil is a mere “illusion,” to which I would answer that it obviously is not.) Put differently, if what God can do is the measure of what is possible, and yet God cannot cause evil (as Aquinas maintains, since God is goodness itself, and as such can only cause goodness, since only goodness has a cause), in what sense is evil a possibility? This is where Leftow is helpful. In the course of his argument that God’s nature is responsible for making even the principle of non-contradiction true, Leftow writes:
It is again a primitive fact about causation that necessarily, every agent makes something like itself, at least directly and immediately. So a hot thing makes heatable things hot. It does not directly and immediately make them cold: it does not directly and immediately produce the intrsinic opposite of heat… A fortiori it does not thus make things hot and cold at once.… God is unlimited … being, esse-ipsum. So His active power extends not to some particular sorts of being, e.g. heatable beings, but simply to beings. God can make only beings, and as a hot thing can heat whatever can receive heat, God can make to be anything that can receive being. God can bring it about that things be, but cannot directly, immediately and per se bring about what is intrinsically opposed to being. (He can bring about non-being per accidens: by making you wise, He makes you not be foolish.) So as a hot thing cannot directly, immediately make something be cold, God cannot bring about the being and non-being at once of any state of affairs, as this is intrsincially opposed to being as cold is to heat. So the making-true of contradictions does not lie within the power of esse-ipsum—because of its own nature… (Leftow, “Power, Possibilia, and Non-Contradiction,” 239-40)
Evil is no more a “possibility” for God (and therefore, I would add, a possibility at all) than cold is a possible effect of heat. Possibility has to do with capacity, and capacity has to do with a thing’s nature or essence. For Aquinas, however, evil can have no nature or essence. Evil is not a thing, but a privation and failure of a thing. Possibility, therefore, is a function of the positive created order, an indicator of the way in which God has made things to be. Possibility is a modality of existence, of which evil is a privation. Evil, accordingly, is not a modality of existence, but a kind of anti-modality, a failure of a thing’s proper mode of being. Possibility is the possibility of being, which is to say, of the good. Evil therefore is not a partaking of the economy of possibility, but is a certain failure to partake of it. Evil is not a form of power, and therefore is not a form of possibility, but a form of weakness and inability. It’s not that evil is impossible, but a “non-possible,” or an “anti-possible.” Possibility has to do with the “doors” God opens or leaves open for a creature; evil is when the creatures slams those doors shut. Leftow’s example of heating and cooling is also felicitous: if one thinks of possibility as an avenue in which created beings can “heat” reality, evil as an anti-possibility represents not a “heating,” but a “cooling” of being. So Parmenides was right after a fashion: only being is possible. Non-being, including the non-being of evil, is not a possibility, but a liability.
A final, historical comment. It is the misunderstanding of evil as a distinct possibility, as partaking of the logic and economy of possibility, that led to such erroneous counterfactual speculations as William Ockham’s claim that God could have created man such that it was meritorious for man to hate God, or the Calvinistic doctrine of double-predestination, which implies that the reprobate are supernaturally (or infernally) ordered toward damnation in the same way that the elect are supernaturally ordered towards their salvation. Both are examples of what Conor Cunningham (The Genealogy of Nihilism) identifies as the nihilistic logic of trying to have nothing (in this case, the nothing of evil) as something.