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.

Wednesday, January 24, 2007

Science Blog Anthology

Bora Zivkovic (coturnix) from A Blog Around the Clock put together a very nice collection of science blog posts. I may be a little old fashioned, but I appreciated even the posts I already had read a bit better in book form, seated in my favorite chair.

Tuesday, January 23, 2007

Re-reading Pirsig

From notes in an old journal, I know I first read Robert M. Pirsig’s Zen and the Art of Motorcycle Maintenance in 1982 (it was first published in 1974). I read his second book, Lila, shortly after it came out in 1991. I recently re-read them, and I have a greater appreciation for his (idiosyncratically expressed) philosophy than I had the first time through. In fact, I think he was pretty much on the right track. (BTW, I read a recent interview with Pirsig here -- hat tip to the Market Metaphysics blog.)

What I originally absorbed from “Zen” (philosophically speaking – I should say it is also a compelling novel) was mostly negative: Pirsig saw fit to basically indict all Western philosophy. Starting with Plato and especially Aristotle, those darn philosophers broke down the ineffable mystic oneness of reality into cold bloodless conceptual categorizations and led us astray. Given my own youthful contemporaneous interest in eastern philosophy, I embraced the criticism, but didn’t really grasp any positive import from Pirsig’s proposal of “Quality” as the supreme notion: I would have been just as happy with Zen, Tao or Brahman.

Now, by the time I read Lila, I was on the same page with Pirsig regarding the deep problem of the subject-object ontological division, which seemed to lie at the root of many seemingly intractable philosophical difficulties (most obviously the mind/body problem). Around this time I was reading Continental philosophers who I thought had taken on the challenge of bridging this divide (most notably Heidegger and Merleau-Ponty). The idea I was exploring was one of activity or process as the central entity. Pirsig seemed to agree, although it seems again that Pirsig’s specific talk of “dynamic quality” or “patterns of value” still didn’t resonate. (Also, I should digress to mention that Lila is much less compelling as a novel compared to “Zen”, and much of the book consists of social commentary/cultural criticism which doesn’t inevitably follow from the philosophy IMHO).

In the intervening years since 1991, the most interesting part of philosophy to me was the debate over conscious experience in the philosophy of mind. The fact that I believe the debate points toward a panexperientialist solution is a touchstone for a lot of the discussion on this blog. And it is the idea of placing experience (or a network of experiential events) into the center of metaphysics which I think shows a tie to what Pirsig was talking about.

To see this, let’s first shift from “Quality” to “value”, which Pirsig endorses in Lila: In chapter 4 (on p.58 of my 1991 hardcover), he says “Quality was value. They were the same thing.” Well, value is inherent in an experience; it is an aspect of the intrinsically intentional first person participation in an event. Pirsig then actually identifies value with experience on p. 66: “It is an experience” (Emphasis original). Value, according to him, exists in the interaction – it is more fundamental than the subject-object division, it is “Between the subject and object…” For me, at various subsequent points in the text, if I substitute the term experience or “experiential event” for quality or value, things begin to make a lot of sense.

At various points in Lila, Pirsig explains how he thinks his perspective points to solutions to various philosophical conundrums. For example, in Chapter 8 (p.102-3): “To say ‘A causes B’ or to say that B ‘values precondition A’ is to say the same thing.” The way I put it (inspired by Gregg Rosenberg and an interpretation of QM): in addition to the effective/dispositional side of a causal event, there is equally an experiential/receptive side. Further on in the chapter he criticizes substance as a derivative and misleading ontological category, again asserting the primacy of “value”, in tune with the endorsement of an event ontology here on the blog.

And of course, arguing that value (or dynamic quality) is ontologically prior to its division into subject and object directly addresses the origin of the mind/body problem in the same spirit as panexperientialism. As he says late in the book (Ch 29, p. 365): “Pure experience cannot be called either physical or psychical: it logically precedes this distinction.”

Wednesday, January 10, 2007

The Limit of the Bayesian Interpretation

I read the paper “Subjective probability and quantum certainty” by Carleton Caves, Christopher Fuchs, and Rüdiger Schack; this is the latest in a series of papers which make a compelling case for the superiority of a Bayesian or subjective interpretation of quantum probabilities. (For a discussion of another paper in the same spirit, see this prior post). To bring the point home, this particular paper features the discussion of quantum experiments with a certain outcome: the authors show that this outcome is to be interpreted as a certainty of epistemic belief on the part of the observer, not an objective certainty.

While I am persuaded that the Bayesian interpretation does win out over attempts to see quantum probabilities (or quantum states) as fully objective, there is a limit to how satisfying the analysis can be as an overall ontological interpretation of QM.

Here's a very brief summary. The authors note the fundamental category distinction in Bayesian probability theory between probabilities and facts. Probabilities cannot be reduced to facts; facts (the truth values of propositions) are used to update prior probability assignments.

In the context of a QM experimental setup, the quantum states are “catalogues of probabilities for measurement outcomes...” which “…summarize an agent’s degrees of belief about the potential outcomes of quantum measurements.” What might be less obvious is how to correctly interpret the preparation procedure. According to a common Copenhagen reading of the situation, the preparation procedure is described classically and the facts about the procedure determine the quantum state. (To reiterate, in the Bayesian interpretation probabilities can never be wholly determined by facts).

The authors set out to show that “the posterior state always depends on the agent’s prior beliefs, even in the case of quantum state preparation (emphasis original)”. The preparation device must be considered quantum mechanical also. The contribution of this paper uses the example of a certain (probability =1) experiment to present the following argument: If you posit that pre-existing properties fully determine the experimental outcome, this will violate the principle of locality (the authors make use of the Kochen-Specker theorem in the argument – the argument is presented in section 5). Therefore we cannot interpret a measurement as revealing an objective pre-assigned value. Certainty means certainty of the agent’s belief.

So, what’s the problem? No problem, just an observation of the limit to how helpful this in forming an ontological interpretation of QM (and, to be fair, the authors finish the paper by making clear they don’t claim this is the answer to all foundational questions). It seems precisely clear where the limit is. In the interpretation: “A probability is an agent’s degree of belief…” The agent and the agent’s degrees of belief are primitives in the implied ontology. There is no explanation or description of the agent, quantum mechanical or otherwise.

If quantum mechanics describes our world, we would like a generalized ontology which makes no distinction between an “agent” and any quantum system. I guess there are two ways to think of this: first, we could try to come to grips with a theory in which all quantum systems, even simple ones, are somehow agents which have beliefs. Offhand I don’t see how this can work. The second option (and my preference) is that we take the probabilities out of the subjective realm and put them (the quantum states) back into reality. The trick is that we have to do this in a way which respects the findings of the Bayesian analysis, meaning the quantum state can’t be considered fully objective. The solution would seem to be to consider the quantum state (between preparation and measurement) to be a propensity of the system under consideration which exists relative to the measuring system. You still have a dichotomy between facts (measurements/interactions) and probabilities (propensities), but both have their own form of existence. (Note my use of term “propensities” here is distinct from the usual Popperian sense which I gather does see them as objective).

Just like at the end of my previous post on this topic, I’ll note that the idea of generalizing the Bayesian approach to ubiquitously cover all quantum systems attracts me to a relational interpretation of QM. Matt Leifer had a good discussion of challenges facing the relational interpretation at Quantum Quandaries (here and here). Many of his points centered around the problem of how simple quantum systems could “choose” a consistent measurement basis. I’m interested to watch and see if these issues can be worked out. A paper was posted last year by Paul Merriam which takes an interesting approach to addressing some of these issues. I'll see if I can summarize it in a future post.

Tuesday, January 02, 2007

Making Abstract Truths Intelligible

The problem with abstract objects is that their existence seems required to provide truthmakers for our propositions about them. Nominalist and other deflationary accounts can’t adequately meet this requirement. Yet how could abstract objects be real if they aren’t part of our concrete world? In modern discussions, abstract objects are causally inert by definition. If they somehow exist in some platonic realm, how could we know them in the absence of any causal connection? (A previous post on abstract objects is here).

Well, we have been considering here a model of causality that incorporates abstract modal realism. The concrete world is a causal network of events which are actualized possibilities. The set of possibilities available to be actualized in an event is constrained by preceding or adjacent events but the outcome isn’t fully determined prior to a new actualization. Unactualized possibilities may be considered “abstract” in that they are non-concrete yet real, and abstract seems as good a term as any for this mode of being (see note on terminology at end of post).

So a certain kind of abstract entity does enter into causal connections. Specifically, the concrete events of the world make contact with abstract possible events. Then the question is can we use this theory to make sense of our seeming knowledge of abstract truths, such as the prototypical logical and mathematical ones?

Well, I don’t have a developed model of how our macroscopic brain/body system would accomplish this. But given the centrality of modality to our reasoning, and given an independently motivated theory that we, as natural systems, exist in a web of actualized possibilities, we can try to connect the dots. The idea would go something like this: we have a direct primitive acquaintance with possibility, which we leverage into knowledge of idealized abstract truths through a process of counterfactual analysis. It is this notion of “primitive” acquaintance which makes this process not just a matter of conceptual or psychological construction, but a matter of reaching toward metaphysical truths.

Terminological note: it is easy to get misled by terminology here and I have probably been sloppy at times. Often in discussions of modal realism (See SEP article on Actualism), a distinction is drawn between the “actual” and “mere” possibilia. Unless one subscribes to David Lewis’ model of modal realism, where possible worlds are all concrete and the term actual is an indexical, I suggest using actual and concrete interchangeably and ask the reader’s forbearance to not misread the fact that possibilities are “non-actual” as saying they don’t exist. They exist, but are non-concrete, hence abstract.