Wednesday, April 15, 2009

Revisiting Actualism

Modal truths regarding possibilities and necessities need truthmakers, as much as anything does. If we conclude that our actual world cannot provide these truthmakers, this implies that reality must outstrip the actual: modal realism is the thesis that we must include possibilities in our reckoning of what exists. Actualism is the name for stances which would limit reality to the actual, and yet try to find adequate ground for modal truths.

This post is repetitive of previous ones (prior posts detailing my readings and evolving views on modal truthmaking are listed below), but I continue to think about this a lot, and recently read some new papers by philosophers on the topic. It struck me that there is something insightful about the insistence of some actualists on grounding modality in the features of the actual world.

Hardcore Actualism

These papers reminded me that in addition to the dispute between modal realists and actualists, another dividing line involves the use of worlds as truthmakers. Most often, modal realism is associated with the use of concrete possible worlds as truthmakers (as proposed by David Lewis). However, some actualist accounts make use of worlds as well, but propose that they still be considered part of the actual world, treating them as abstract or fictional, etc. (What makes this a bit confusing is that a model using abstract worlds could also be considered modal realism if the worlds truly transcended our own – existing platonically rather than as sets of propositions or “world-stories” or whatnot).

Actualism which rejects worlds of any sort is referred to as “hardcore” actualism in this paper by Gabriele Contessa. He favors this approach, as does Jonathan D. Jacobs in this paper. Jacobs explicitly endorses a power-property based approach to grounding modal truths.

A motivation for hard-core actualism is that our intuitions tell us that possibilities are grounded in the properties or causal powers of actual things. This is especially true if we consider the local, everyday, possibilities of life. I could have gone for a run this morning (although I didn’t). I know this is true because I have the natural capacities needed to do so, and in fact, it is something I often do. Why do I need to postulate something as extravagant and disconnected as a possible world (at which my counterpart did run) to provide a truthmaker for this homely fact?

Power-properties as truthmakers?

Jacobs makes reference to a number of philosophers who favor an approach which grounds modal truths in properties of actual things (one is Alexander Pruss, whose work I had commented on once here). There are two problems with these that I see. The first critique often raised is that these accounts seem ill-equipped to deal with more distant, but still intuitive possibilities. It seems possible that our universe might not have existed at all – what properties of the “actual world” could ground this possibility? I will leave this problem aside for now, because I think it might be addressable if we had an answer for a more pressing second problem. This is the fact that the power-property accounts I have seen to-date, while differing in their ontological set up, treat the powers (or dispositions) as entailing their manifestations. The entailment relation seems to assure (to my reading) that given two instances of precisely identical power-property complexes, the same manifestation would occur (I discussed this previously in the context of George Molnar’s work here).

So while the theory asserts that the powers could ground possibilities, in fact I don’t see that they really do the job. In my example, it appears my natural powers ground the possibility that I could have gone for a run, but the relation between power and manifestation in these theories doesn’t seem to explicitly account for the indeterminism involved here: if we somehow could “rewind the tape” and replay the events of this morning, what aspect of the ontology accounts for the fact that the manifested outcome REALLY could have been different?

Propensities at Work?

I have thought (with quantum mechanics in the back of my mind as usual) that instead of powers entailing their manifestations, the properties involved should be seen as propensities: causal powers with truly probabilistic rather than entailed outcomes. The set of unactualized possible outcomes, in this case, are real – they are rooted (and constrained) by prior actuality, but are not just theoretical entities. If this is right, then we’re not, strictly speaking, talking about actualism, anymore, of course, but a species of modal realism. However, at least the hard core actualist might be pleased that we’re not creating entire worlds out of whole cloth. Possibilities are manifestations -- I see them as events or event complexes -- they are not worlds.

What about possible worlds semantics?

Jacobs is so disenchanted with possible worlds as truthmakers, however their reality is conceived, that he wants to develop a replacement for the traditional modal semantics which utilizes worlds, and sets out on a path toward constructing an alternative. Fortunately, a good thing about my idea, I think, is that we can have a firmer basis for rationally constructing abstract worlds based on our acquaintance with these real local possibilities. Basically, we utilize the “replaying the tape” notion and utilize what we know about how probabilistic causation works in the actual world to construct alternatives for how the world could have been different. (This kind of approach was discussed by philosophy student Damon Woolsey in his modal realism papers – see here; also, Richard Chappell used the rewind/playback metaphor in a paper here). The further back you take this rewinding, the more distant possibilities you can envision. Note that counterparts are a bit different in this scheme – it seems either I’m in a world or I’m not given how they are constructed.

Can the set of these sorts of “worlds” ground the truth that our actual world might not have existed at all? Maybe – if you allow me to conceive of an initial probabilistic event which turned out to be the first seeding of our universe, but which was in no way guaranteed.

A Bloggy Exploration of Modal Truthmaking and Modal Realism
(in chronological order)

Whole Lotta Worlds
Notes on reading David Lewis’ On the Plurality of Worlds

Armstrong on Modality
About my inability to find modal truthmakers in D.M. Armstrong’s book Truth and Truthmakers

The World is Not Enough
On Actualism and Modal Fictionalism

Notes on Plantinga’s Modal Realism
A self-explanatory post title!

Local vs. Global Possibility and the Link to Causality
Alexander Pruss’ Aristotelian approach

Modal Realism, Modal Rationalism
Musing on how we know about modal truths

Modal Tenses
Parallels between modal and temporal metaphysics

Woolsey’s Modal Realism
An intriguing paper by Damon Woolsey found on the internets

Modal Problems with the Theory of Powers
Critique of powers as modal truthmakers in George Molnar’s theory

Actual as Indexical, After All?
Multiverses – Physical and Metaphysical
2 posts with more of my own musings


Anonymous said...

Hi VS Bandaneer here,
What the actual may be is itself
open to interpretation ---as much as is the possible. What is the definition of actual, for instance?
Or, real, or sensual, or perceived or any of the terms which
are likely to come up. Actual versus--what? Nominal? Mental?
How to parse the mental from the physical---back to the mind / body split again---and that is intractable.
So, no, I just don't believe your scheme really does make things clearer or easier---but it does clrify the difficulty--and that certainly is valuable.

Steve said...

Hello and thanks for your comment. You raise difficult questions. I might try to define actual as what is causally connected with me. The possible is the "rest" of reality. But any definition can lead to further questions.