Thanks for the clear explanation of mereological nihilism. I came across the same challenge when researching Superficialism and I'm wondering if it's because the position is relatively new.
I'll quote Hawthorne for a definition on the Superficialist argument:
"Taken at face value, ontological disputes are substantive disputes about how the world is
[...] Superficialist in ontology think that, at least for very many disputes of this sort, this face value construal of them is incorrect: very often disputants are talking past one another, on account of having attached different meanings to the key terms of the debate" (Hawthorne, 213)
https://philpapers.org/rec/HAWSIO
Hawthorne thus proceeds to put forward three arguments, broken into sections, about how this deflationary approach towards ontological disputes is ultimately unfounded. He focuses on the approach developed by Eli Hirsch, of whom he thinks has the most defensible position on Supericialism.
I'm very sympathetic towards the stance that metaphysical disputes are meaningful, and so I'm biased to agree with Hawthorne's arguments. So that you can engage with me I'll do my best to summarize the three sections here, but please note that I'm no longer under any philosophical tutelage and I may unintentionally mischaracterize his argument:
Section (I) Verificationism
Hawthorne asserts that there is a resistance on the part of those who are Superficialist leaning to adopt or be characterized as "full-blooded verificationist." So, rather than stating that ontological disputes are misguided because there's a lack of correspondence between the statements and the concrete world, Superficialist (Hirsch, in particular) apply 'conciliatory translation schemes' to disputes to demonstrate that they are ultimately speaking the same truths just with differing understand of the terms being used.
Hawthorne undermines this by demonstrating that if Superficialist accepts certain ontological disputes then there is no good reason why they should deny others (here he draws up some disputes between endurantist and perdurantist).
Section (II) Intensional Issues Disclaimer: I freaking love this argument. Also one of the arguments I really had to mull over and re-read This section is where Hawthorne utilizes a hypothetical dispute between a mereological nihilist and an anti-nihilist.
According to the Superficialist, because disputants are often just talking past each other then in a debate between an anti-nihilist and a nihilist, Superficialist will view these arguments as being unable to intensionally (this concept was particularly difficult for me to understand) advance over one other.
- After ruminating, I took it to mean that ontologists will propose differing necessary or sufficient conditions for their possible worlds and the objects therein that either overlap and can contradict each other or that the other ontology can deem as being a falsehood and misunderstanding of reality which can be overlooked.
During this section, Hawthorne shows anti-nihilist and nihilists do intentionally advance over one another and can, from this intensional advancement, proceed to have a substantive debate on the differences in their ontologies. As opposed to a Superficialist interpretation which would try to deflate the debate between these two as ultimate saying the same thing using conciliatory translation schemes.
I'll leave it at this for now as these first two sections have a lot to unpack in themselves. I'm really looking forward to your take on this! Thanks again!