Can something good be the cause of evil? Aquinas on “per se” vs. “accidental” causality

Tolkien’s metaphysics of evil, part 11

The previous post suggested that viewing Tolkien’s fictional representation of evil from a specifically Thomistic perspective may put us in a position to appreciate (better, at least, than many scholars have been able to do) the simultaneous coherence of Tolkien’s portrayal of evil and its paradoxical complexity. I went on, however, to note those respects in which Thomas’s own metaphysics of evil is quite conventional or traditional in its basic Augustinian or Christian-Neoplatonic outlook.

Where Thomas does finally depart from or at least improvise upon the traditional Augustinian reckoning of evil, according to Carlos Steel his innovations are more Aristotelian (and therefore still Socratic and Greek, in Steel’s view) than they are distinctly Christian. To resolve the perplexity left open by Augustine and earlier Neoplatonists as to how evil actions are caused, Thomas in question 49 of the Summa applies the Aristotelian distinction between per se and accidental causality.[1] In contrast to classical Neoplatonism’s typical denial that evil has an efficient cause, Thomas begins the corpus of his first article with an emphatic affirmation that “every evil in some way has a cause” (ST 1.49.1).[2] As the “absence of the good which is natural and due to a thing,” there must be a cause to explain why anything should “fail” or be “drawn out” from its “natural and due disposition.”[3] Thomas nevertheless agrees with the Neoplatonic premise that “only good can be a cause, because nothing can be a cause except in so far as it is a being, and every being, as such, is good.”[4] The question, then, is how something good can cause evil. Thomas’s answer is that what is good is able to cause evil, not insofar as it is good in itself (per se causality), but only accidentally. An accidental cause of an effect is a cause that produces an effect not intentionally, but by producing some second, unintended effect with which the first, intended effect is somehow accidentally connected. As we will see in a future post, it is this Aristotelian distinction between per se and per accidens causality that Aquinas applies to the question of how the rational will is ever able to do or choose evil while intending something good.

[1] Steel, “Does Evil Have a Cause?”, 259. Thomas finds the distinction, for example, implied in chapter two of book five of Aristotle’s Metaphysics and applies it to the problem of the causality of evil. Aquinas, Commentary on the Metaphysics of Aristotle 5.3.781 and 789. (See also On Evil 1.3. Aristotle also distinguishes between per se and accidental causality in his discussion of chance in Physics 2.5.) Steel, however, implies that the application of Aristotle’s distinction between per se and accidental causality to the problem of the causality of evil was actually original with Aquinas, whereas Denis O’Brien points out that Plotinus also used the distinction to explain how the soul becomes evil through its contact with matter: “The soul becomes evil, when she does so, only ‘accidentally’, and, even then, only through the presence of matter.” O’Brien, “Plotinus on Matter and Evil,” 184, citing Plotinus, Enneads 1.8.12 and 14. As John Milbank also observes (“Evil: Silence and Darkness,” 21), preceding Aquinas in his notion of the accidental causality of evil is Pseudo-Dionysius, who writes that “evil exists as an accident. It is there by means of something else. Its source does not lie within itself. Hence something we do for the sake of the Good looks right and yet is not really so when we consider to be good what is actually not so.” Pseudo-Dionysius, The Divine Names 4.32.

[2] “[O]mne malum aliqualiter causam habeat.”

[3] “Quod autem aliquid deficiat a sua naturali et debita dispositione, non potest provenire nisi ex aliqua causa trahente rem extra suam dispositionem…”

[4] “Esse autem causam non potest convenire nisi bono: quia nihil potest esse causa nisi inquantum est ens, omne autem ens, inquantum huiusmodi, bonum est.”


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