Powers vs. Humean Supervenience

I’ve been interested in ontological accounts which feature dispositional properties (also known as dispositions or powers) in the starring role.  This intriguing draft paper, “Goodbye, Humean Supervenience”, by Oxford's Troy Cross, sets out to show that David Lewis’ Humean supervenience program (which seeks to reduce everything to a mosaic of categorical properties) fails, since it can be reinterpreted as a system where Lewis’ fundamental properties are in fact identical to dispositions.  This implication can’t be rejected without abandoning the account of properties as sets of possibilia.   The possibility unattractive feature of the dispositional doppelganger of Lewis’ story is its appeal to nonlocal circumstances as the trigger for the manifestation of the powers.  My notes on the paper follow.

An Improved Supervenience Base?

Brian Weatherson (home page, blog) has authored an SEP article on David Lewis. In it he ably takes on the difficult task of summarizing in a few dozen pages the work of one of the most prominent and productive philosophers of the latter part of the twentieth century.

One section addressed something I had idly wondered about Lewis. As Weatherson discusses in his section 5, entitled “Humean Supervenience”, much of Lewis work involved reduction: whether the subject was the mind, language, laws of nature, or causation (modality was a rather spectacular exception), he presented arguments that all the truths about a world ultimately supervene on a set of (perfectly natural) properties and relations in that world. He then argued that these, in turn, are intrinsic properties of point-sized objects and spatiotemporal relations. (The “Humean” aspect of this is that he follows the spirit of Hume’s “dictum” that there are no necessary relations between distinct entities.)

What I had wondered was: did Lewis ever acknowledge that his picture of locally distributed point-sized objects in a space-time container was a classical view, inconsistent with modern physics?

Those who challenged this aspect of Lewis’ work over the years argued that his supervenience base is incapable of supporting some of the truths about the world, and so his attempts at reduction fail. However, most critics haven’t quibbled with the assumptions about physics, rather they argue that some additional higher-level properties and/or relations need to be added to explain the world. Even many materialist philosophers think additional brute metaphysical structure beyond the basic physical entities is required (this debate was the subject of this old post); some philosophers think necessary connections are needed to explain causation; dualists will see a need for fundamental mental properties and perhaps psycho-physical laws.

But, Weatherson notes that a second way to argue against Lewis’ project is indeed to point out that modern physics is inconsistent with Lewis’ notions. At a minimum, he says, quantum physics seems to need non-spatiotemporal relations to explain Bell’s theorem.

Weatherson explains that Lewis was indeed aware that his picture was inconsistent with quantum physics, but still thought it was extremely valuable to defend the thesis regardless of that fact. Weatherson explains the idea as follows: to the extent his picture of physics is wrong, it is because physics has more content in it (e.g. entanglement relations) rather than less. So, if Lewis can successfully defend reduction of various folk theories on his terms, it will remain a valuable accomplishment.

That makes sense, but I still wonder if explicitly reckoning with quantum physics and its interpretation couldn’t helpfully reframe these philosophical debates. There is more to the shift from classical physics to quantum physics than just adding some non-local connections. There is the quantum measurement event itself, which I see as an ineliminable new addition to the basic constituents of nature. I think that mind and causation might be the targets of successful reduction given an improved supervenience base which featured a network of measurement events in its basic ontology. (Also, one neat thing about taking this approach is that we could hold on to Hume’s dictum. He may not have known about QM, but I think the indeterminism involved in measurement events is consistent with his insight.)

Whole Lotta Worlds

I enjoyed reading David Lewis’ On the Plurality of Worlds. Of course, for me it was like entering a theater in the third act: my eclectic self-education has big holes in it which inhibit my comprehension of such a work.

The usefulness of expressing modal concepts in terms of possible worlds seems clear enough (here’s a blog post which outlines this well – hat tip to the latest philosophy carnival). David Lewis argues that the value and utility of possible worlds in modal thinking points to a metaphysical or ontological argument that the full set of possible worlds exists concretely. In the book he defends this thesis.

Most other philosophers would say possible worlds are abstract, like mathematical objects. Even setting aside that the ontological status of mathematical objects is highly controversial topic, Lewis moves from his usual modest tone toward vehemence in criticizing these views as insufficient in supplying the full structure needed for possible worlds; further the question of how the actual world is selected from the set of abstract possibilities is either inadequate or “magical” in competing accounts.

In other words a sufficient proposal for a modal metaphysics either needs to have Lewis’ ontological panoply of concrete worlds, or else we need a fuller account of the ontological status of the abstract world along with a detailed mechanism for selecting the actual world (in Lewis’ scheme, “actual” just means the world we happen to be in, but there is nothing else special about it relative to the other worlds). Note that this means a system with only one actual concrete world and no ‘abstract realm+selection’ endowment is simply an inadequate metaphysics. While Lewis takes this for granted, I think it's interesting that seemingly only a small subset of philosophers would endorse either the Lewisian system or an abstract alternative with full mechanisms for addressing the Lewisian critique. They are presumably content to deal with modality in epistemological and linguistic arenas unburdened by the metaphysical worries.

While Lewis doesn’t explicitly address it much in this book, the other way to parse the metaphysics is in terms of causality. Lewis’ approach enables him to be a Humean about causality. Everything in the world just happens. If we want to talk about what counterfactual situations could have possibly happened to us, say, then we are talking about things that happen to our counterparts in other worlds. If we want to say there is only one concrete world where things happen and these are caused in a way which could have happened differently (they are contingent things), then we need a model of “real” causation that can handle this selection process. These two alternatives exclude the common assumption many seem to share that there is only one world, but a simple billiard ball notion of causation is all we need. In such a world there is no possibility or contingency at all. Again, this would be an inadequate metaphysics.

So, what do I think of Lewis’ proposal? I don’t like the Humean/fatalistic aspect of it. I would like to think a selection process happens rather than think that every possible world exists in an even-handed way, and we just happen to be in one. But at this point this is a preference on my part, not an argument.

What I get out most out of this is what I’ve been emphasizing in this post: Lewis is an obstacle to those who think they can “get away with” a minimalist metaphysics like single-world physicalism. It’s not enough.