Full Idea
I assume it is metaphysically impossible for a proton to have a different causal role, ...which is plausible because a proton would appear to have no identity at all apart from its role in causal processes.
Gist of Idea
A proton must have its causal role, because without it it wouldn't be a proton
Source
Brian Ellis (Scientific Essentialism [2001], Intro)
Book Reference
Ellis,Brian: 'Scientific Essentialism' [CUP 2007], p.2
A Reaction
This seems to be a key idea in scientific essentialism, which links essentialism of identity with essentialism in the laws of nature. Could a proton become not-quite-a-proton?