A basic confusion

In Uncategorized on March 23, 2010 by Jenny

I have a very basic question about Lewis’s seminal “Counterfactuals” that I hope can be cleared up rather easily.

Lewis says that A –> C is nonvacuously true if and only if C is true at all the closest A-worlds.  But how do we determine what are the closest A-worlds?  More broadly, how do we determine whether one world is closer to the actual world than another one?  I know that sameness of laws is important, check!  But what else?

And need we be very precise in our determinations of which worlds are closer than other worlds?  Or, for the purposes of counterfactual analysis, do we just have to get things roughly right?

Thanks for your help,



3 Responses to “A basic confusion”

  1. “But what else?”

    Well… everything! The similarity or dissimilarity of any given fact goes into such a judgment. I found useful the analogy he draws to making similarity judgments among people. There’s no exact rubric to draw-on, but we feel reasonably comfortable with the relevant trade-offs between traits (and certainly enough to communicate with each other about it).

    Possible world semantics always starts to feel dodgy to me when we try to talk about very fine-grained differences. However, Lewis is attempting to provide an analysis, not give a tool for investigation. As such, he needn’t worry with prescriptions that will allow us to determine which worlds are closer for very difficult cases (he wants to talk about primitive relations and avoid being committed to some controversial standard that would allow him to do so). But that’s okay, since most of the time we’re not dealing with difficult cases. For instance, in the nearest possible world in which I don’t type this response, I can be more than pretty sure that this response doesn’t get posted (and therefore that my typing causes the response). Such straightforward judgments are enough for Lewis to build a theory on.

    Thinking about difficult cases further though, it seems that one way to connect Lewis’ view to philosophy of science is to look at controlled experiments as a tool for trying to find out about close possible worlds. They allow us to see (close enough for jazz) what would happen in a nearby world were one variable is different. A significant amount of debate in science could then be construed as debate about which possible world is closest–e.g. whether or not a scientist actually isolated a variable.

  2. This is a long standing difficult question for using “closest possible world” in our analyses. It may just be difficult to specify the weights of various similarities and differences, but I worry that our own biases will end up being the decisive factor. Most people will think that there is an objective fact about what causes what, though our interests will perhaps pick out certain causes as more salient for our purposes. However, I saw Christopher Hitchcock give a talk this weekend in which he denied this objective sense of causation and suggested that causality will be permeated by our norms and judgments concerning the influences of various factors. As far as Lewis is concerned, however, I think we can understand him as simply trying to capture the basic way in which claims of causal dependence ought to be evaluated. He need not tell us exactly what makes one world more similar than another (though we probably will need to do so at some point). What Lewis needs is a framework for providing a basic understanding of the counterfactuals on which his analysis of causal dependence rests. The details concerning how to rank world can then be filled in later.

  3. I have some intuitive ideas. Let me know if they’re wrong.

    The closest world to our world is our world itself. Two worlds can be similar at least in two ways: (1) sameness in laws, and (2) facts in the world.

    So, the possible world where I am a person is closer to our world than the possible world where I am an inanimate object. And, the possible world where gravity exists on Earth is closer to our world than the possible world where gravity doesn’t.

    It seems that two worlds are close only *relative* to something. It’s hard to say which of two specified worlds (world1 and world2) are closer to a given world (world3)when there is a vast number of facts and laws to look up to, while some laws exist only in world1 and world3 and some facts only exist in world2 and world3.

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