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Posts Tagged ‘explanation

Laws before facts

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Does the universe come “facts first” or “laws first”? That is, in terms of metaphysical priority, do the non-nomic facts determine what the laws of nature are, or are the laws at the ground floor determining what the non-nomic facts are? (Or maybe neither grounds the other; I’ll ignore this view for now.) The best-known example of a facts-first theory is Lewis’s “best system” account: to be a law of nature is to be a member of the set of generalizations over the non-nomic facts that has the best balance of simplicity and strength. Here are two rough-and-ready arguments against an account like that. The first is the circularity argument I gestured at a few weeks ago:

  1. The laws explain the non-nomic facts.
  2. If Y explains X, then X does not explain Y.
  3. If X grounds Y, then X explains Y.
  4. So the non-nomic facts don’t ground the laws.

And this is the second:

  1. The non-nomic facts are many and disparate; the laws are simple and few.
  2. Prefer metaphysical theories that are simpler and more parsimonious at the fundamental level.
  3. So prefer laws-first to facts-first metaphysics.

The second premise is a methodological principle, rather than a general metaphysical claim (hence the imperative). It’s a ceteris paribus principle, and so the conclusion is a ceteris paribus conclusion: there is a presumption in favor of laws-first accounts.


Written by Jeff

April 18, 2009 at 6:57 pm

Non-distributive explanations

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This distribution principle looks awfully plausible:

  • A explains (B and C) iff (A explains B and A explains C).

But I think it might be false, at least in the right-to-left direction.

A potential counterexample comes from Aristotle. A bandit is lingering by a road, and a farmer is walking home down the same road. By chance (as we would say), they meet at place X at time T. There is a telic explanation in terms of the bandit’s purposes for his being at X at T, and there is a telic explanation in terms of the farmer’s purposes for his being at X at T. But there is no telic explanation for their meeting, even though I take it that their meeting just consists in both of them being at X at T. The meeting is just a coincidence.

Slightly more carefully: let BP be the bandit’s purposes and FP be the farmer’s purposes, and let BXT and FXT be the relevant location facts. Assuming that antecedent strengthening holds for “explains”, this means that (BP and FP) telically explains BXT, and (BP and FP) telically explains FXT. But since their meeting is coincidental, it seems plausible that (BP and FP) does not telically explain (BXT and FXT).

If distribution fails for telic explanation, then perhaps it fails for nomic explanations as well, for the same kind of reason.

Why does this matter? It’s relevant to my criticism last week of Lewis’s “best system” account of laws (not just my criticism). Briefly, I said: on Lewis’s account, the qualitative facts explain what the laws are, but the laws should explain the qualitative facts. That makes a very tight explanatory circle, and that’s bad.

A response might go: it’s true that the conjunction of the qualitative facts explain the laws. It’s also true that the laws explain each individual qualitative fact. But it doesn’t follow that the laws explain the conjunction of the qualitative facts—since the distributive principle fails—and so there is no bad explanatory circle.

Written by Jeff

March 10, 2009 at 4:38 pm

Posted in Epistemology, Metaphysics, Science

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Magnetic laws

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I’ve been thinking more about the problem of fit I posted last week. Specifically, I’m trying to work out how a response appealing to reference magnetism would go.

Recall the puzzle: how is it that when we select hypotheses that best exemplify our theoretical values, we so often hit on the truth? A simple example: emeralds, even those we haven’t observed, are green, rather than grue. And lo, we believe they are green, rather than believing they are grue. It seems things could have been otherwise, in either of two ways:

  1. There might be people who project grue rather than green, in a world like ours.
  2. Or there might be people who (like us) project green, in a world where emeralds are grue.

Those people are in for a shock. Why are we so lucky?

A response in the Lewisian framework goes like this. Not all properties are created equal: green is metaphysically more natural than grue. In particular, it is semantically privileged: it is easier to have a term (or thought) about green than it is to have a term (or thought) about grue. This should take care of possibility 1. If there are people who theorize in terms of grue rather than green, their practices would have to be sufficiently perverse to overcome the force of green’s reference magnetism. There are details to fill in, but plausibly it would be hard for natural selection to produce creatures with such perverse practices.

But this still leaves possibility 2. Given that our theories are attracted to the natural properties, even so, why should a theory in terms of natural properties be true? The green-projectors in the world of grue emeralds have just as natural a theory as ours, to no avail.

But even though 2 is possible, we can still explain why it doesn’t obtain. What we need to explain is why emeralds are green—and we shouldn’t try to explain that by appeal to general metaphysics, but by something along these lines: the electrons in a chromium-beryllium crystal can only absorb photons with certain amounts of energy. That is, we explain why emeralds are green by appeal to the natural laws of our world.

Generalizing: “joint-carving” theories yield true predictions because their predictions are supported by natural laws. Why is this? On the Lewisian “best system” account of laws, it is partly constitutive of a natural law that it carve nature at the joints: naturalness is one of the features that distinguishes laws from mere accidental generalizations. So, much as reference magnetism makes it harder to have a theory that emeralds are grue than it is to have a theory that emeralds are green, so the best system account makes it harder to have a law that emeralds are grue than it is to have a law that emeralds are green. Then the idea is that, since our theories and our laws are both drawn to the same source, this makes it likely that they line up. Furthermore, since the laws explain the facts, this explains why our theories fit the facts.

Something isn’t right about this story; I’m having a hard time getting it clear, but here’s a stab. There’s a general tension in the best system account: on the one hand, the laws are supposed to explain the (non-nomic) facts; on the other hand, the (non-nomic) facts are metaphysically prior to the laws. But metaphysical priority is also an explanatory relation, and so it looks like we’re in a tight explanatory circle. (Surely this point has been made? I don’t know much of the literature on laws, so I’d welcome any pointers.)

This is relevant because the answer to the problem of fit relies on the explanatory role of laws—a role that seems difficult for the best systems account to bear up. But I feel pretty shaky on this, and would appreciate help.

Written by Jeff

March 2, 2009 at 8:44 pm