Humility and constraints on O-language

In "Ramseyan Humility," David Lewis argues that we cannot know what the fundamental properties in our world are. His arguments invoke the possibility of permutations and replacements of fundamental properties. Most responses focus on Lewis's view on the relationship between properties and roles, and on the assumptions about knowledge that he makes. I argue that no matter how the debates about knowledge and about the metaphysics of properties turn out, Lewis's arguments are unconvincing since they rely on a highly implausible assumption about the expressive power of our language.