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January 23rd, 2007

Martians and the Gruesome

One of my quirkier philosophical views is that the most pressing question in metaphysics, and perhaps all of philosophy, is how to distinguish between disjunctive and non-disjunctive predicates in the special sciences. This might look like a relatively technical problem of no interest to anyone. But I suspect that the question is important to all sorts of issues, as well as being one of those unhappy problems that no one seems to even have a beginning of a solution to. One of the issues that it’s important to was raised by Brad DeLong yesterday. He was wondering why John Campbell might accept the following two claims.

I don’t know why Campbell accepts these claims. And I certainly don’t want to accept them. But I do know of one good reason to accept them, one that worries me no end some days. The short version involves the conjunction of the following two claims.

The long version is below the fold. (This is cross-posted to CT, so I’ve filled in more of the background than I usually would here.)

The story starts with some relatively banal observations about explanation and understanding. [1] Imagine that I throw a stone at a window, it strikes the window with momentum m, and the window breaks. Now one way to explain the window’s breaking is to say that it was struck by a stone with momentum m. But while that might be in some sense a complete explanation of the breaking, there are other explanations that promote greater understanding. This explanation doesn’t make explicit the salient fact that the window’s shattering was not particularly dependent on the precise momentum of the projectile, or that the projectile was a stone. Someone who explains the breaking in terms of it being struck with a projectile of momentum between m1 and m2, where these are the rough limits for what is (a) sufficient to shatter the window and (b) plausible given that I threw the projectile, seems to have a better explanation of the shattering, and a greater understanding of why the window shattered.

It’s tempting to conclude at this stage that if one explanation explains an event in terms of some particular being F, and another explains it in terms of that particular being G, where being F entails being G but not vice versa, then the second explanation provides a deeper understanding of what happens. In short, broader explanations (explanations that are made true in more ways) are better. But that principle seems to have clear counterexamples. Imagine a third ‘explanation’ that says the window broke because it was either struck with a projectile of momentum between m1 and m2, or struck by a window-breaking spell. This explanation is even broader than the two previous, since the truth of the explanans is entailed by, but does not entail, the truth of the explanans in the previous cases. But it is, intuitively, a worse explanation than what came before. It certainly doesn’t provide a deeper understanding. Indeed, someone who offers this ‘explanation’ has very little understanding of why the window broke.

Still, it seems a qualified principle might work. Broader explanations are better as long as the terms they use are not disjunctive. The idea that some terms are disjunctive and others aren’t goes back at least to Goodman’s Fact, Fiction and Forecast. Goodman famously defined up a new term grue. Something is grue, I’ll say, iff it is green and observed or blue and unobserved. As Goodman noted, observing lots of emeralds and seeing they are all grue provides us with no reason to think the next emerald we see will be grue. This kind of simple induction doesn’t work when dealing with terms like ‘grue’. Various authors, most importantly David Lewis have argued that the distinction Goodman pointed towards, between disjunctive terms like ‘grue’ and non-disjunctive terms like ‘green’, has many implications for across philosophy. Following tradition, I’ll call the ‘grue’-like terms gruesome, and ‘green’-like terms natural. (And I’ll often suppress the fact that the difference between gruesomeness and naturalness is a matter of degree, as there are a spectrum of cases in the middle.)

So what we want for understanding, I think, are explanations that are as broad as possible but not involving gruesome terms. Or perhaps explanations that strike the best balance between breadth and gruesomeness. I’ve only ‘argued’ for that by a single case, but the principle seems pretty plausible to me. At least it’s plausible enough to be the first half of my reason for believing a position like Campbell’s.

Now the relatively difficult part. It’s easy enough when talking about toy physical explanations to say what are natural and gruesome terms. It is, to say the least, somewhat harder to do the same thing in special sciences. Is the term ‘seasonally adjusted fall in sales’ natural or gruesome? By the standards some philosophers use, it is pretty gruesome because it is explicitly defined relative to calendar dates. (After Goodman’s work it wasn’t too hard to find philosophers saying this was a tell-tale sign of the gruesome.) But there are very good explanations that make use of terms like this. For a simpler case, is ‘weekday’ a natural or gruesome term? Again, it looks pretty gruesome from the perspective of micro-physics. But it is hard to explain/predict/understand traffic patterns without talking about weekdays and weekends. Progress here is not going to be easy.

David Lewis proposed that how gruesome a term is could be a function of the shortest definition of that term in terms of fundamental physics. But that also looks to rule out most special science explanations out of court pre-emptively. We have no idea how to define, say, a rise in demand for widgets in terms of micro-physics, but I bet that any such definition will be immensely complicated. So complicated that if we took Lewis’s idea seriously, we’d say that explanations of anything in terms of rising demand for widgets would be impossibly gruesome. But such explanations can be perfectly good. So Lewis’s idea fails.

The problem is that no one seems to have a better idea. One constraint on an answer is that we can’t use the contents of mental states in the answer, because there is good reason to think that the naturalness of various terms is part of what makes our mental states have the content that they have. (Again, see Lewis for the arguments for this.) The best answer I know of that doesn’t appeal to beliefs, intentions etc of humans is Lewis’s answer in terms of definition length. And that’s a non-starter I think.

So no one really knows how to answer, or even to make much of a start on answering, the following two questions.

The two questions might be related. If there is an answer to the first question that relates the naturalness of special sciences to facts about micro-physics in some relatively straightforward (or at least Turing computable) way, then one way to know what’s natural and what’s gruesome would be to find out all the micro-physical facts, and then do the relevant computation. (That is, the answer to the parenthetical question is yes.) But we don’t know whether such a metaphysical story is true.

What we do know is that we didn’t find out that terms such as ‘cell’, ‘belief’, ‘society’ or ‘demand’ are (relatively) natural by their relation to micro-physics. One somewhat troubling (to reductionists like me) prospect is that the only ways to find out the naturalness of these predicates is something like the way we found out that they are natural. (Not that we know what that way is either.) And if that’s right, it’s possible that the Martian physicists can’t tell the natural from the gruesome terms in biology, psychology, anthropology, economics, etc.

If that’s all correct, then I think there’s a pretty good sense in which the Martian physicists won’t understand human behaviour. (Or, for that matter, the behaviour of all sorts of complex systems. The particular kind of way that human brains are complex might not be doing very much work in this argument.) They might know all sorts of counterfactuals saying that if certain objects were different in certain ways, then certain events would not have come about. But knowledge of such counterfactuals only consistitutes understanding if the ways in question are relatively natural. Remember, someone who takes the best explanation of the window’s breaking to be that it was either struck by a projectile with momentum m or a spell doesn’t really understand why the window broke. And that’s the case even though had the window not been struck by a projectile with momentum m or a spell, it wouldn’t have broken.

I think there’s a case to be made that, for all we now know, the Martian physicists will be in an analogous position with respect to understanding/explaining our behaviour. And that’s why I think, or at least worry, that Campbell’s position might be true. And it’s one of several reasons I worry about us lacking any story about what makes special science terms natural.

1 Banal these may be, but I wouldn’t have learned of them if not for discussions with Michael Strevens. Many of the important points relevant to this post are discussed in this paper (PDF), especially in section 5. Michael has a book on explanation coming out some time in the near future which I very highly recommend.

Posted by Brian Weatherson in Workbench

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2 Responses to “Martians and the Gruesome”

  1. Mark van Roojen says:

    It seems (to me) like the need for a special science is partly that the explanation of what we are explaining at the level of any of the more general sciences is relatively gruesome when considered at the level of the more general science. So that makes me think that the gruesomeness of a predicate shouldn’t depend on how it can be connected to terms at the level of the more general science. It should be some feature of the explanation at the special sciences level, rather than a feature of how that level relates to other levels.

    So then I think, maybe it is partly a function of how simply the terms function to explain the phenomena at some level given the phenomena at that level and the description of what we are trying to explain. (Maybe there are other constraints besides these.) But that makes me worry that the story brings in human interests in a way you seem to want to avoid, at least for a good number of the special sciences. If I want to explain why the price of something fluctuates in a certain way, the thing I am trying to explain is already something that I picked out at a certain level of description which may already be quite messy if described at thelevel of a more general science. And the fact that I picked that out as what I wanted to explain seems a function of my interest.

    I don’t think this means that what is gruesome at a level depends on human interests, but we may have special sciences for a level only when humans have an interest in phenomena at that level where there is no non-gruesome explanatory unification of the relevant phenomena at the level of a more general science.

    I’m not sure if this is on point, useful or hopelessly naive, but the main point is just that it seems to me that gruesomeness ought to be something that depends on what is going on explanations at a level, not on how that level relates to other levels.

  2. jed says:

    The answer to these questions seems obvious, so I must not understand them correctly. I’ll briefly explain what seems obvious, and someone can tell me what I’ve missed.

    [I]s ‘weekday’ a natural or gruesome term?

    “Natural”, in these sense that it picks out a wide range of patterns that can be found easily by generic statistical analysis without reference to human culture or language. From the “martian” point of view, a time-series analysis of large ambulatory bags of water contaminated with various fats and proteins shows a bunch of statistically significant cycles, including one with a seven day period (in most but not all regions of the globe). In this cycle five contiguous days are more like each other than like the other two days. QED.

    Similarly for seasonal adjustment of any observed quantity.

    Concepts like “demand for widgets” are much more complex, depending on a set of nested distinctions. However I think the burden of proof should be on those who claim that widely used explanatory concepts don’t attach to some sort of regular structure in the world. Of course opponents of explanations such as “witchcraft” have accepted and discharged this burden in the past. This is what James Randi does, for example.

    Finally, I don’t understand the emphasis on micro-physics. It strikes me as a red herring.

    To see why, let’s say the martians, from orbit, can measure the location of the various ambulatory water bags from minute to minute, using the Martian equivalent of radar. (We can assume they completely understand their radar on a micro-physical level but I don’t see why that makes any difference.) But say the resolution of the Martian radar only tells them roughly how big the water bags are and where they are — say to within a decimeter. Why should the martians care about the micro-physics of water bags, if they can extract the patterns they care about from this rough measurement?

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