What Kind of a Theory is Originalism?

Mike Rappaport has an interesting post about how to justify originalism. In particular, Rappaport writes about what kind of a theory originalism is. Is it a “normative” theory (what kind of theory would produce good policy), an “interpretive” theory (what kind of theory actually assesses the meaning of the document) or what I’d called a “positivist” theory (what kind of theory best conforms to what the law is today)?

Personally, I am most sympathetic to the positivist arguments for originalism, but I’ve noticed that a lot of confusion in theoretical debates about originalism seems to stem in part from confusing these three different kinds of arguments. Rappaport apparently plans to write more posts about the issue, which I look forward to reading.