Because most people do understand it epistemically/subjectively?
No. Most English language speakers use modal terms both epistemically and metaphysically. My point was that most people, both lay- and academic, do not use 'p is (metaphysically) possible' to mean 'p is not ruled out by the laws of physics'. If they did, then they wouldn't understand anthropic arguments that presuppose the contingency of the physical laws themselves.
I think there are many kinds of possibility and many kinds of laws
Then I don't know what claim you're making anymore. Taboo 'law'; what is it you're actually including in this 'law' category, potentially?
I think the kinds of possibility have a family resemblance, and there is no issue of dsicarding the other kinds in favour of epistemic possibility.
But you still haven't explained what a 'merely possible' thing is. If logical and nomological possibility are metaphysical, then you owe us an account of what kinds of beings or thingies these possibilia are. On the other hand, if you reduce logical and nomological possibility to epistemic possibility -- logical necessity is what I can infer from a certain set of logical axioms alone, logical possibility is what I can't infer the negation of from some set of axioms, nomological necessity is what I know given only a certain set of 'natural laws'.... but if we epistemologize these forms of necessity, then we collapse everything into the epistemic, and no longer owe any account of mysterious 'possible worlds' floating out there in the aether.
do not use 'p is (metaphysically) possible' to mean 'p is not ruled out by the laws of physics'. If they did, then they wouldn't understand anthropic arguments that presuppose the contingency of the physical laws themselves.
If that is meant to indicate there is some specific sense of possible that is used instead, I doubt that. Consider the following:
A: "Are perpertual motions machines possible?"
B: "I don;t see why not"
A: "Ah, but theyre against the laws of thermodynamics "
B: "Ok, they.re impossible".
A:
One of the few things that I really appreciate having encountered during my study of philosophy is the Gettier problem. Paper after paper has been published on this subject, starting with Gettier's original "Is Justified True Belief Knowledge?" In brief, Gettier argues that knowledge cannot be defined as "justified true belief" because there are cases when people have a justified true belief, but their belief is justified for the wrong reasons.
For instance, Gettier cites the example of two men, Smith and Jones, who are applying for a job. Smith believes that Jones will get the job, because the president of the company told him that Jones would be hired. He also believes that Jones has ten coins in his pocket, because he counted the coins in Jones's pocket ten minutes ago (Gettier does not explain this behavior). Thus, he forms the belief "the person who will get the job has ten coins in his pocket."
Unbeknownst to Smith, though, he himself will get the job, and further he himself has ten coins in his pocket that he was not aware of-- perhaps he put someone else's jacket on by mistake. As a result, Smith's belief that "the person who will get the job has ten coins in his pocket" was correct, but only by luck.
While I don't find the primary purpose of Gettier's argument particularly interesting or meaningful (much less the debate it spawned), I do think Gettier's paper does a very good job of illustrating the situation that I refer to as "being right for the wrong reasons." This situation has important implications for prediction-making and hence for the art of rationality as a whole.
Simply put, a prediction that is right for the wrong reasons isn't actually right from an epistemic perspective.
If I predict, for instance, that I will win a 15-touch fencing bout, implicitly believing this will occur when I strike my opponent 15 times before he strikes me 15 times, and I in fact lose fourteen touches in a row, only to win by forfeit when my opponent intentionally strikes me many times in the final touch and is disqualified for brutality, my prediction cannot be said to have been accurate.
Where this gets more complicated is with predictions that are right for the wrong reasons, but the right reasons still apply. Imagine the previous example of a fencing bout, except this time I score 14 touches in a row and then win by forfeit when my opponent flings his mask across the hall in frustration and is disqualified for an offense against sportsmanship. Technically, my prediction is again right for the wrong reasons-- my victory was not thanks to scoring 15 touches, but thanks to my opponent's poor sportsmanship and subsequent disqualification. However, I likely would have scored 15 touches given the opportunity.
In cases like this, it may seem appealing to credit my prediction as successful, as it would be successful under normal conditions. However, I think we perhaps have to resist this impulse and instead simply work on making more precise predictions. If we start crediting predictions that are right for the wrong reasons, even if it seems like the "spirit" of the prediction is right, this seems to open the door for relying on intuition and falling into the traps that contaminate much of modern philosophy.
What we really need to do in such cases seems to be to break down our claims into more specific predictions, splitting them into multiple sub-predictions if necessary. My prediction about the outcome of the fencing bout could better be expressed as multiple predictions, for instance "I will score more points than my opponent" and "I will win the bout." Some may notice that this is similar to the implicit justification being made in the original prediction. This is fitting-- drawing out such implicit details is key to making accurate predictions. In fact, this example itself was improved by tabooing[1] "better" in the vague initial sentence "I will fence better than my opponent."
In order to make better predictions, we must cast out those predictions that are right for the wrong reasons. While it may be tempting to award such efforts partial credit, this flies against the spirit of the truth. The true skill of cartography requires forming both accurate and reproducible maps; lucking into accuracy may be nice, but it speaks ill of the reproducibility of your methods.
[1] I greatly suggest that you make tabooing a five-second skill, and better still recognizing when you need to apply it to your own processes. It pays great dividends in terms of precise thought.