In a previous post we learned that Aristotle grounded the truth of modal statements – particularly those about possibility – in the causal powers of substances. Whether something is possible, impossible, or necessary at a certain time depends on which substances exist and what they can bring about at that time.
Aristotle’s view of modality has several merits. First, causal power seems to be a basic feature of our experience of the world. It is basic in the sense that it resists our attempts to break it down into simpler concepts and it plays a key role in our explanation of the most general phenomena in our world. According to Jonathan Schaffer (2007), general phenomena such as laws of nature, probability, processes, production, counterfactual dependence, and the direction of time are perhaps best analyzed in terms of causation – not the other way around (2.1.2). And if so – if causation is indeed a bedrock concept, then it will likely illuminate the nature of modality as well.
I say “illuminate” instead of “reduce” because modality is already assumed when talking about causation in terms of powers – e.g. having the power to undergo or produce a change already involves modal cognates like can, cannot, and must. So the Aristotelian cannot do away with modal talk altogether. Nevertheless, he will insist that modality is fundamentally causal in nature, and that powers are superior to other theories that ground modal truth in platonic entities (the propositional primitive view) or other-worldly counterparts (extreme modal realism).
In line with Aristotle, Pruss (1996) offers several reasons why he thinks powers do a better job of illuminating the nature of modality than competing theories do: “in ordinary language, the notion of ability is arguably more basic (cf. Place, 1997), and from it general notions of possibility are obtained by extension. We have personal knowledge of ability, e.g., in the way Kant outlines in the second Critique through recognizing ourselves as morally responsible for an evil act and thus as having been capable of doing otherwise. There is also less mystery about capability than there is about modality in general since capabilities are actual properties of actually existing things, and so the account is indeed helpful. And at the very least, if this approach worked, it would reduce modal talk in general to a particular subset of it” (pp.35-36).
Along with Pruss (1996), I would add that a theory of modality is preferable (ceteris paribus) insofar as it posits truth-makers that are epistemically accessible – and Aristotle’s powers do that job quite nicely. As embodied creatures, we often experience powers directly or indirectly when we manipulate objects in our surrounding environment and make inferences based on the traces those objects leave behind.
Thus, when it comes to knowing truth-makers for statements like “possibly, I am jumping”, it is straightforwardly a matter of knowing whether I presently have the capacity to jump. I need not invoke mysterious truth-makers such as non-actual jumpings in spatio-temporally isolated worlds (extreme modal realism) or abstract propositions in a platonic heaven (the propositional primitive view). Compared to these alternatives, Aristotle seems to be on firmer ground.
But what about the drawbacks of his view? One serious objection to Aristotle’s theory is the difficulty is has accounting for the possibility of universes that are radically different from our own. What do I mean by this? Remember that for Aristotle, some events in our universe could have been different because past substances had the power to bring those alternatives about. But what if our universe (and its substances) had never existed in the first place? What if a radically different universe had existed instead? Indeed, what would make that universe (and its unique history) possible? These are very difficult questions to answer if the only resources for grounding possibilities are the substances in our universe! Thus, it is no surprise that the historical Aristotle simply denied the possibility of universes (and histories) radically different from our own (Pruss, 1996, p.191). Contemporary metaphysicians take this denial to be a rejection of what are called “alien possibilities.”
Yet, the rejection of alien possibilities is not the only option available to an Aristotelian. According to Pruss (1996), one can either “(1) deny that the whole course of history [could have been] different, (2) accept that it could have been different due to the causal agency of an ahistorical non-person, or (3) accept that it could have been different due to the causal agency of an ahistorical person, by all accounts a God” (p.191). Both (2) and (3) posit a substance (or collection thereof) that exists beyond any universe and whose powers ground every possibility, alien or otherwise. As we shall see in next week’s post, the Leibnizian solution to the grounding problem embraces option (3) by arguing that the powers of an omnipotent Person best account for alien possibilities.
 David Hume would undoubtedly disagree by arguing that the apparent experience of causing while manipulating objects is merely a matter of habit – that we only observe “willings” which are regularly followed by “movings” – not a causal connection between the two. Regrettably, I do not have space to address Hume’s objection here, but you may consult Richard Swinburne’s essay entitled Why Hume and Kant Were Mistaken in Rejecting Natural Theology for a condensed response.