Comments Elsewhere

Given that the antecedent conditions are never satisfied in the actual world, it seems that both (A) and its negation are consistent with the actual physical phenomena. Presumably (A) is false, but it could be true of a world otherwise identical to our own, couldn’t it?

In order to be certain that this is true, don’t you have to hold that members of natural kinds don’t have any of their dispositional properties essentially?

If members of natural kinds (say, lead) have dispositional properties (say, chemical stability) essentially, then it may very well turn out that (for example) any possible world where you have X-shaped lead is a possible world where that lead will not transmute into gold. There might be possible worlds where leaden stuff does that, but that would be a possible world with an alien substance, unknown in our world, not a possible world with lead.

It’s open to you to claim that members of natural kinds only have dispositional properties contingently. But that will require some argument; it’s certainly not obvious to me, at least, that certain chemical dispositions aren’t part of the essence of (say) salt or gold or lead, or that certain biological dispositions aren’t part of the essence of (say) slugs or tigers or bats.

Alternatively, it’s open to you to claim that falling under a natural kind can entail having certain dispositional properties, but deny that natural kind membership supervenes on the “totality of our world’s actual spatiotemporal properties,” i.e. you could have possible worlds with perfectly identical “actual spatiotemporal properties,” but have one of them containing lead and the other containing an alien substance that’s like lead except it transmutes under the right (as-yet unfulfilled) conditions. But you’d have to give me some pretty burly argument to convince me that natural kind terms aren’t part of the basic description of the properties of the world as we know it. I don’t know how you’d even begin constructing a complete description of a world without ever using a natural kind term. (“Well, you see, these two worlds are exactly identical in their physical properties. But in W1 there is water and in W2 there is not.” Well, then, they’re not exactly identical in their physical properties.)