Here are some brief thoughts on papers I read recently on the metaphysics of powers/dispositions.
I thought “A Powerful Theory of Causation” by Rani Lill Anjum and Stephen Mumford was an important paper. The authors set out to show that powers have the right degree of “modal strength” to support a theory of causation. Powers have been long thought to necessitate their manifestations, and necessity (and the sense of constant conjunction) is too strong to describe causation. The notion of metaphysically necessary connections in nature has long supplied a basis for arguing against powers and associated theories of causation. Anjum and Mumford say that powers (dispositions) “dispose” toward their manifestations, but don’t necessitate them.
One way of seeing that powers fall short of necessity is to note that when placed in a context, a disposition can be enhanced or, importantly, hindered by other powers. The authors use a vector addition model as a heuristic to see how this works. Only when the sum of vectors (with various strengths and directions) exceeds some threshold do we get the manifestation.
In later sections of the paper the authors deal with various potential objections and place their theory in a historical context of the difficulties faced by causal models, showing again that the unwarranted assumption of necessitation was the key stumbling block.
While the vector model was interesting, my favorite section of the paper (section 5) deals with explaining probabilistic causation. Here Anjum and Mumford endorse a propensity (propensity=probabilistic power) interpretation for a single disposition. I myself think this is the key to understanding how powers can have the right modal strength “all the way down”; it also has the virtue of fitting with our best physical theory of how the actual world works (quantum mechanics).
I eagerly look forward to a forthcoming book from Mumford and Anjum called Getting Causes from Powers – this will elaborate upon the theory in greater detail. Also note that a podcast and slides from a recent talk by Stephen Mumford from the PhilSci forum at UMB (Norwegian University of Life Sciences) are available here (scroll down for previous talks). It is a very nice introduction to powers, and focuses on contrasting a powers approach with a laws-based theory of causation.
Some quick takes on other papers.
Michael Esfeld argues that a metaphysics of powers has an advantage in terms of compatibility with physics in his paper “Humean metaphysics versus a metaphysics of powers.” In the paper, Esfeld summarizes the difference between a Humean approach and the powers approach: in contrast to the above he does characterize powers as having necessary connections with their manifestations. However, he does then describe the option of treating powers as propensities to explain probabilistic causation. His main point in the paper is that while physics can be compatible with more than one metaphysical picture, the powers model is the best fit given the commitment of physics (and other sciences) to describing dispositional and functional properties.
William A. Bauer takes up the issue of the ontological grounding of powers in "Four theories of pure dispositions". Can they exist without depending on categorical properties for their being? What is the nature of powers when they aren’t manifesting if they lack such grounding? He reviews several approaches to this problem, and concludes that the best model is one where they are self-grounding via a continuous low-level manifestation (which is distinct from their more pronounced, distinguishing potential manifestation).
This was a thought provoking paper, which prompted me to go back and review others on this topic, including Mumford’s “The ungrounded argument”, Neil E. Williams’s response “The ungrounded argument is unfounded”, and Stathis Psillos’s 2006 paper “What do powers do when they are not manifested?”. My quick two cents on this issue is inspired by QM and the idea of powers as propensities: I think powers have a real-but-not-concrete status akin to possibilities in a framework of modal realism. Unlike a static notion of possibilia, however, propensities causally impact our world through their disposition toward actual manifestation events. This is again consistent with QM: between measurement events, quantum systems don’t have concrete existence, but they certainly exist in a causally relevant way, as their influence on events is apparent and measurable.
Finally, I note with interest that two philosophers have recent papers endorsing the Heil/Martin view of powers as inherently qualitative: Jonathan D. Jacobs in “Powerful qualities, not pure powers”, and Robert Schroer, in “How far can the physical sciences reach?”. Both make for interesting reading, as do other papers by these authors.
Here is a list of prior posts on powers/dispositions (chronological).
George Molnar and the Powers That Be
Powers and Property Dualism
Modal Problems with the Theory of Powers
John Heil Gets Very Close
Suarez on Quantum Propensities
Notes on C.B.Martin's The Mind in Nature
Powers vs. Humean Supervenience
Abilities vs. Dispositions