Jonathan Ichikawa suggests a disarmingly simple argument that fragility is not intrinsic; consider a fragile material object like a glass slipper. A exact intrinsic duplicate of the slipper in a world with different laws of nature might not be fragile; perhaps glass slippers are used as hammers in those worlds.
I think the first stage in responding to this is to invoke the weak nomic necessitarianism which is a part of dispositional essentialism. Any world in which there exist stable glass slippers is a world in which something extremely close to the usual laws of electromagnetism hold. But any world in which these laws (or something extremely close to them) hold is also a world in which glass slippers are fragile. This response is an instance of the argument form deployed by Bird in Bird, A. 2001. Necessarily, salt dissolves in water. Analysis 61: 267–74 – in later work, he calls it the ‘down-and-up structure of laws’.
This, however, merely shifts the question to whether an intrinsic duplicate of a glass slipper is possible which does not obey the laws of electromagnetism. It would not be made of glass (Ichikawa concedes this point in the comments, at least for the sake of argument), but nor could it involve instantiations of mass and charge – these, by weak nomic necessitarianism, obey the laws they do by necessity.
But perhaps there are possible intrinsic duplicates of glass slippers which are made of glassch, and involve instantiations of schmass and scharge. The argument could then run as follows: these glassch schlippers are not fragile, but they are intrinsic duplicates of glass slippers, so fragility is not preserved over intrinsic duplication, and fragility is not intrinsic.
The obvious place to resist this second argument is the premise that glassch schlippers could be intrinsic duplicates of glass slippers. Ichikawa seems to motivate this by the claim that both glass slippers and glassch schlippers could have atomic structure XYZ. But this still seems wrong. Glassch schlippers are made of schatoms, not atoms, so they don’t have any atomic structure at all, let alone the same atomic structure as glass slippers.
At this point, the only way I can see to resurrect the argument that fragility is not intrinsic would be to make a strongly structuralist move , and say:
1) that the identities (quiddities) of the properties involved in an object are irrelevant to that object’s structure.
2) that the structure (and only the structure) of an object is preserved under intrinsic duplication.
Now most metaphysicians would demur from at least one of these claims, and hence they can recover the view that fragility is intrinsic. But I’m tempted by both claims, since I reject quiddities altogether. Must I then say that fragility is extrinsic?
Not if I make the stronger necessitarian move of denying that schmass, scharge and therefore schlippers are possibilities. This requires a necessitarianism stronger than WNN (see my previous post for discussion of grades of nomic necessitarianism). SNN certainly permits this response. Does FNN permit it? Only if schmass and scharge do not number among the genuinely possible fundamental natural properties. If FNN is true, this is not a question we can answer on a priori grounds. So if, as I suspect, FNN is true, then whether fragility is intrinsic is a question whose answer we can only know a posteriori.