There’s been another free will dust-up over at Jerry’s place, but that doesn’t much interest me at the moment. (It’s the usual hundreds of comments from quasi-confused incompatibilists and correct-but-not-always-patient compatibilists.)
What I’m more interested in right now is the distinction between what is “actual” and what is “possible.” An important part of my story (in Chapter 6, for anyone who’s keeping track) is that an important part of the actual world is its modal structure. That is, facts about what is real include facts about what is possible. (And you don’t really understand what is real unless you understand what is possible and what is not.)
This came up in conversation with someone named Tom (who blogs here, apparently). Tom wrote:
We don’t even know whether billiard balls are subject to necessitating determinism, and the claim that they are (i.e. that the billiard ball could have moved some other direction) is non-empirical and thus non-scientific. Observation only ever shows us actualities, not mere possibilities. (Philosopher William James noted this.)
And I replied: “James is wrong that we only observe actualities.” I never quite got back to explaining how wrong James is about determinism (another time perhaps), but I did go on to explain:
I agree that “mere possibilities [don’t] emit particles” (although quantum mechanics might complicate this), but it’s worth considering what “observations” in physics are like.
What particle physicists try to measure is scattering amplitudes – that is, the Hamiltonian, the dynamical law that governs the quantum field. They do this by having a bunch of detectors that register such things as the energy and charge of particles that result from some high-energy collision. Then, if they get enough registrations in a certain window, they might conclude that a Higgs boson must have been among the sources of the particles that were detected.
Note that if/when the physicists claim that they have observed the Higgs that this claim epistemically rests on their knowledge of the dynamical laws (which is a specification of what is possible) and that in turn rests on a bunch of dynamical properties (mass, energy, charge) which are also essentially nomic in character (charge tells you what something can do).
Now you might say that what the physicists “really observe” is the computer output from their various instruments, but going down that road will land in the swamp of claiming that the “actuality” we “really observe” is just sense data, or what have you.
Perhaps I should say that I’m inclined to say that facts about what is possible are themselves part of the actual world. I’m suggesting that the distinction between the actual and the possible (or between the categorical and the dispositional) is not metaphysically robust. So you shouldn’t read me as thinking that there’s some robust “mere possibility” that’s completely “non-actual” that we observe.
(1) As for physical measurements, I guess it seems to me that modal premises don’t need to appear in the justifications for physicists’ beliefs. Instead, aren’t they just saying, ‘As a matter of fact, all actual particles explode in such-and-such a way?’ Or appealing to probabilistic laws?
If they’re actually appealing to alethic necessities, I would suggest that they’re appealing to non-empirical premises somewhere. That’s perfectly fine for rationalists such as me, but still supports the point that observation /alone/ doesn’t confirm determinism. (For example, if they’re using an induction, the Humean problem shows that they need a non-empirical premise.)
(2) As for facts about the possible being part of the actual, I think there’s a sense in which that’s true. Perhaps, for example, merely possible worlds are actual entities. (They are, I think, if they’re maximal consistent sets, or Lewisianly concrete.) And possibilists would say that there really “are” mere possibilia.
But at the very least, I take it, you think there’s a distinction between the actual and the non-actual. That’s part, then, of the distinction between the actual and the merely possible. The rest of it is to say that some of those non-actual things could have existed. You agree to that, too, right? Is there anything more to the concept of the merely possible than the non-actual but possible?
And I responded”
“aren’t they just saying, ‘As a matter of fact, all actual particles explode in such-and-such a way?’”
Well, metaphysical commitments will vary (even within a single researcher, depending on context), but I’d say that the explanatory robustness of laws speaks against deflationary accounts.
“I would suggest that they’re appealing to non-empirical premises somewhere”
Of course they are. The point is that mere observation (or “pure empiricism,” if you like) gets you nothing but phenomenal solipsism.
If you want to buy into the common-sense notion that we observe stars and cells, and that physicists observe muons and quarks, then your going to need to countenance some strong modal facts. And in so doing, it’s going to be just as legitimate to say “I’ve observed that this is possible and this isn’t” as it is to say “I’ve observed a quark.”
And a similar point will apply to Hume. If you consistently apply his standards of justification, you don’t just end up with a problem of induction, you end up with total skepticism. Hume is presumably OK with that, but we’ll be misled if we think that it’s only induction that lands us in Hume’s pickle.
“there’s a distinction between the actual and the non-actual.”
Of course there is. My point is that we sometimes observe “nomic” or “dispositional” facts just as much as we observe so-called “categorical” facts. But seeing that something is possible is not the same thing as seeing that it is actual. I might feel that the glass is fragile, but that doesn’t mean that it’s actually broken.