Wednesday, October 26, 2005

The World is not Enough

Picking up the thread on modal metaphysics (most recent post here): If I follow Armstrong’s truth/truthmaker approach to metaphysics and I insist it apply adequately to modal truths regarding necessity and possibility, it seems to lead (contra Armstrong’s own conclusion) to a modal realism involving possible worlds. David Lewis is the leading proponent of the theory that all possible worlds exist concretely. So what are the specific strategies for those who want to avoid joining Lewis? I “hit” the Stanford Encyclopedia of Philosophy to learn more. A brief summary of two relevant articles is below (keep in mind that this stuff is new to me and I’m even more prone than usual to misreading something – please check out the source articles if you’re interested).

There are two broad options here. First, try to deny any need to appeal beyond our single actual world. Second, substitute an account of abstract entities for Lewis’ concrete ones. This latter approach I will come back to in a future post.

Christopher Menzel wrote the SEP article called “Actualism”. Actualism is the thesis that there are no non-actual individuals or worlds. The article discusses various strategies to defend this thesis. Menzel discusses modal logic, and the fact that the simplest modal logic can be made to generate theorems which are troubling to the actualist. One of them is something like this: the statement {it’s possible that a flying pig exists} implies the statement {there exists something which is possibly a flying pig}. Next, he then summarizes how Kripke and others introduced modifications to modal logic meant to prevent the derivation of these sorts of statements while preserving the ability of the logic to do its modal work. The article leads one to conclude these efforts have not met with success: there isn’t a way to have a fully robust modal logic which has an actualist metaphysics as its analogue.

The article also discusses other programs to defend actualism (“world stories"/"world propositions”) which deflate the status of troubling implied statements into something innocuously only about propositions, not individuals. According to Menzel’s account these attempts also have serious objections – mainly they don’t do justice to analyzing the role modal statements really play in our language and thought. (He also devotes a section on Plantinga’s system of abstract possible worlds; this is something I will spend more time on before commenting).

Another strategy, which Armstrong himself once advocated, is called “Modal Fictionalism” – the SEP Article on this is authored by Daniel Nolan. This is the idea that this talk of possible worlds is a useful fictional construct not meant to be taken at face value. While this sounds attractive, the strategy suffers from objections, too. These include technical objections (logical formulations of modal fictionalism can lead to contradictions or circularity). Also, modal statements have more “objectivity” than authored fictions - if they’re not actual, they would be more like “hard” abstractions (mathematics being the paradigm example). A related point is that modal fictions are incomplete since they suffer from the author’s ignorance about many modal statements. Several other objections are outlined in the article as well.

Now as I said above I’m new to all of this, and it’s possible that some strategy exists or will be developed in the future which does justice to analyzing modal language and its role in rational thought while keeping to a deflationary actualist metaphysics. All I can safely say here is that all the attempts in the literature mentioned in these articles are described as having serious outstanding objections.


Tom C said...

I'm not conversant with all this, but modal stuff is certainly problematic.

Personally, I'm not comfortable with multiple possible worlds. For one thing, there's a problem over preserving identities between the worlds. There should be a possible world in which I was born with brown eyes; but if so there should also be a possible world in which I was born as, say, a Japanese woman. But could a Japanese woman be the same person as me? Or look at it another way - if that person in the alternative world is me, how come I haven't got access to his thoughts and experiences? If he isn't me - even if he's me1, who diverged from me only a millisecond ago - then that alternative world isn't a world in which something different happened to me, but a world in which something different happened to someone else.

In fact, I think there is only one possible world in a somewhat stronger sense, and I am therefore inclined to explain concepts like possibilty in terms of things being possible 'so far as we know' or 'within the prevailing laws of physics'. But that doesn't deal with all the logical problems.

Steve said...

If you otherwise could get comfortable with the Lewis system, I think he adequately addresses your issue regarding preserving identities. No, it's not the actual you involved (it couldn't be). If you think its possible that something different could have happened to you at time t, you restate this as: there is a possible world where a counterpart which was identical to you up until time t had this different experience. The fact that he is wasn't the actual you and he no longer is even identical to you beyond time t doesn't seem important in explaining how we typically utilize this sort of modal thinking. (But obviously not everyone agrees with this).

Using the laws of physics does offer difficulties: is it the case that the laws of physics are necessarily the way they are? That doesn't seem right to our intuitions. Are they deterministic? If so, then possibility is an illusion. Are they indeterministic in the sense of including a random component? But if there is only one world, this wouldn't seem to make any difference (there still can be only one outcome - the one we have).

If possiblia are all in our head, we need an account of how abstract entities enter into our thinking - and I'm finding that this is a surprisingly controversial topic as well!

Anonymous said...

Hi Steve,
Alexander Pruss proposed an account of possibility in the line of Plato, Aristotle and Leibniz. See
In this account possible worlds are neither abstract nor concrete entities but objects of intentionality (of humans or god). But for usual purposes there are concrete possibilities in the things themselves. "A non-actual state of affairs is possible if there actually was a substance capable of initiating a causal chain." Therefore there are fewer possibilities as the philosophers think: It is not possible for me that that I'm borne as a Japanese but it is possible for me both that I'm still a illiterate and that I can speak Japanese.
It is very interesting to see how Pruss binds these different accounts of possibility together. I like his proposal. See also his dissertation on

Steve said...

Thanks Tychic, I appreciate it. I will check out the Pruss references.
- Steve