Tuesday, January 30, 2007

Modal Tenses

I want to briefly comment on and recommend this paper by Takeshi Yagisawa called "Modal Realism with Modal Tense" (HT: OPP). It explores the parallels between modal and temporal metaphysics, and suggests that modal realists would benefit from treating the possible and the actual as tenses, in the manner of past and present tense, respectively.

Modal realism can create terminological and conceptual ambiguities which leave it vulnerable to criticism. If we speak of a (metaphysically) possible talking donkey and an actual mute donkey, how is it that the possible donkey is “real” if it isn’t “actual”? So, for the verb denoting reality we’re using (e.g. “is” or “exists”), we should consider creating two modal tenses. The possibility tense is an analog of the past tense; the actuality tense is an analog of the present tense. There is much less ambiguity or confusion when we say “dinosaurs existed”. Existing in the past tense is something we have an intuitive feel for (this is not to say philosophers don’t argue about the ontological status of past, present and future events/objects -- they do it all the time -- it’s just that the modality discussion suffers in comparison due to lacking the built-in toolkit of having tenses for words like “exist”).

There are many more subtleties to this idea than I will mention here and Yagisawa unpacks and presents them carefully. An interesting idea he discusses is a comparison of 2 approaches to modality to 2 parallel views of temporality as follows. If one views the possible and actual modes of reality in an even-handed or egalitarian fashion in the manner of David Lewis, this is analogous to the 4-dimensional or eternalist view of temporality, where different points in time all exist in an even-handed way. If one views the actual as deserving to be called “real” and wish to downgrade the reality of the possible (as in the view traditionally called “Actualism”), this is in the same spirit as presentism, which likewise displays a “chauvinism” in viewing the present as having an exclusive claim on reality.

I have been using the terms abstract and concrete to characterize the possibilities and the actualized events of our world, respectively. I think this is still OK as long as I can communicate it with some context. The appeal of using modal tenses is that it provides another way to introduce a primitive distinction to characterize the possible and actual without requiring either total even-handedness or a deflation of the possible. This was a thought-provoking paper.


Mike Wiest said...

One avenue for arguing that the possibilities are "real" is from within a quantum mechanical description. (Which has the added bonus that it is the most fundamental physical description we have so far, so arguably all our metaphysical discussions should use it.) Maybe you have QM in the back of your mind when you're talking about your ontology of actualized possibilities, but you don't want to scare people off?

Anyhow, one reason to think the quantum possibilities are real and objectively existing is that they interfere with each other and we can measure the consequences of that interference. E.g. in the two slit experiment you wouldn't get an interference pattern when you pass particles through one at a time unless the wave function really existed in some sense.

I thought that it was pretty well settled that the wave-function is objective and not just a measure of an experimenter's ignorance, but I don't know where in the literature that might have happened (Do you?). But there seems to be a resurgence of people taking an epistemic interpretation of QM, so maybe I was mistaken...

Steve said...

You're right that I have QM in mind. Possibilities are real in QM in my view, but they are not "fully" objective. What I mean is that they are mind-independent (one sense of "objective"), but their reality is relativistic, not absolute (absoluteness being a different sense of "objective"). Their nature depends on their interaction with a particular system in a measurement. A "fully" objective treatment of quantum possibility gives you the many-worlds interpretation.
(You've been nice to read and comment on lots of my blog posts, but I will gather the chutzpah to mention that I have written lots of posts on this topic (labled with the "quantum physics" tag). Thanks - Steve

Mike Wiest said...

Sorry! I guess I'll have to dig into the quantum physics archives...

Thanks for your quick replies.

Speaking of different senses of "objective," do you have a discussion somewhere of the apparent paradox or contradiction between consciousness' inherent subjectivity even though it is an objective phenomenon? Or don't you think consciousness has an objective existence?


Mike Wiest said...

Oops--Garbled sentence should read "...contradiction between consciousness' inherent subjectivity and its objective existence".

Steve said...

I don't worry about it in one sense. Subjective points of view exist ubiquitously and independently of my own. Scepticism about their existence is no more satisfactory than skepticism about the external world generally.

In a different sense, the contradiction between the subjective and the objective can be just another way to express the hard problem. How can the third-person (extrinsic) descriptions of physical systems capture first person (intrinsic) experience?