Friday, November 10, 2006

Modal Realism, Modal Rationalism

The case for modal realism can be motivated in a few ways. It often begins with contemplating the everyday modal propositions we make about the world. We seem to know that things might have been different, after all, and there are different ways the world could be in the future. Some dinosaurs might have survived the meteor catastrophe. I might have tried to avoid traffic by leaving earlier this morning. It’s possible that I might stop writing this post now, and finish it later. By virtue of what can these propositions be considered true or false? Being of realist persuasion, I think there must be something in the reality outside our minds to provide truthmakers for these propositions (my prior posts on modality and modal realism can be found here).

Modal realism also seems linked to realism about causality, when the causal connection is seen as a counterfactual dependence. I might not have checked my e-mail: if I hadn’t, I would not have seen your message.

In a deflationary metaphysics where there exists one world subject to deterministic laws, all connections are necessary. Possibility and contingency would only be illusions. They would only exist in our minds. (Likewise it seems to me that the directional flow of time and causality would have no parallel in the world; necessary connections are symmetric.)

But given a naturalistic worldview, our minds arise from the same stuff as the rest of the world. Is it plausible that a world which lacks real possibility would give rise to creatures for whom the notion is indispensable?

Of course, we know strict determinism is false, given the real indeterminism present in quantum mechanics. I have argued elsewhere for an interpretation which sees the quantum states as incorporating real (although not concrete) possibilities, while measurements are concrete actualization events.

Leaving aside for now the tough problem of describing the modal space in any detail (see note below), I am intrigued by the notion that the modal propositions and modal reasoning we employ are grounded in a modal reality.

The thesis of modal rationalism, as explored by David Chalmers in section 10 of this paper, is the idea that our notion of what is conceivable (logically possible) does indeed match what is metaphysically possible. He examines and argues against proposals that these need be distinct modal spaces.

If I couple modal rationalism with a modal realism which posits that metaphysical possibilities really exist (outside the cranium), this creates what I think is a fascinating picture. We, along with all natural phenomena, are continually actualized from a space of possibilities: our roots in this space form the basis of our evolved faculty for modal reasoning.

Note: For a great discussion of how to flesh out the space of metaphysical possibility, and related issues including modal rationalism, I recommend Richard Chappell’s recent draft paper.  [UPDATE 25 January 2010:  here's a link to a pdf of the final paper from Chappell's website.]


Anonymous said...

Very interesting post, Steve, as usual.
Two main concerns come to my mind.

First, what we consider that accounts as a 'real' possibility.
Even from a folk philosophy stance, it seems to me that we tend to a deflationary position about the space of possibilities.
Somehow we consider plausible the possibility that "some dinosaurs might have survived the meteor catastrophe", but implausible the possibility that "pink elephants might have".
Aren't we already including some kind of epistemological a-priori constraint for that space of possibilities?

Second, the description that you point out to: "the quantum states as incorporating real possibilities".
Wouldn't it be close to a form of inclusive physicalism: the ground base of 'reality' as a sort of quantum entanglement (of possibilities)?

Thanks again for your thought provoking posts,
Antonio Franco

Steve said...

Hello Antonio:

Thanks for your comments.

For me, the distinctions you are making among possibilities can be thought of as “local” or more “distant” cases, but all would be “real” metaphysical possibilities if they are a priori conceivable. So, “it is possible I might stop writing now” is very local; “dinosaurs might have survived” more distant; and “pink elephants are possible” very distant. I think of this notion of distance (following Richard Chappell) in terms of “rewinding the tape” of the world to varying degrees, and replaying to see what different possibilities are actualized. When contemplating the very distant and “weird” possibilities, please consider that metaphysical possibility includes the idea that the laws of nature could have been different (going beyond nomological possibility).

I like your phrase of inclusive physicalism. Because physicalism is very often identified with eliminative views on consciousness, I might prefer to say inclusive naturalism. The only reason I think the ground of possibilities may go beyond the idea of the entanglement of quantum states is because the states which exist are constrained by events which have already happened (Formally, quantum states measure possibilities between measurements). Whereas full possibility requires the "rewind".

Anonymous said...

Yes, Steve, I'm reading with great interest your links to Richard Chappell's papers and your comments. I feel really refreshed by his neat exposition. I tend to get very tired with semantic dimensionalism and all that, and can't help the feeling of the different status of this actual world against the background of possible worlds (to me more like 'models' or 'representations'). So, it is comforting to me Richard's proposal graphically encapsulated in the expression "The Actual World is not a Possible World".
But, as you accurately comment, this could face the reservations against ersatzism. Richard thinks that the ersatzist views can be made to work. And I really trust that programm, just for my mental sanity.

About 'inclusive physicalism', I borrowed the term from Jeffrey Gray, though I guess I'm using it in a more intuitive sense. For a very interesting overview of Gray's work, check Uriah Kriegel's recent paper in his web page,[]here[/url]

Thanks for your helpful clarifications,
Antonio Franco

Steve said...

I wanted to also mention that the discussion on quantum states has me thinking more about how far to take the realism of possibilities. It could be that the local possibilities which constantly arise are real but the more distant possibilities (as defined above) are our mental extrapolations. I'm not sure about this.