I have known some pretty smart people who were caught flat-footed by the philosophical tool of object replacement
Can you elaborate? What is the tool of "object replacement"?
It is essentially what Harris did in the article. He replaced the noun objects of Armstrong's point with other, analogous/isomorphic objects to illustrate that the point being made did not have the merit that Armstrong thought it did.
I'll see about looking up the term as it applies to Propositional Logic. It's a more widely recognized term (at least here).
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).