The interpretive significance of the Constitution's positivity in a classical natural law jurisprudence

At The Originalism Blog, a recent post by Mike Rappaport distinguishes among "three main arguments for originalism" and explores a hybrid approach "that views the original meaning as the law, not based on positivism, but based on a normative or idealized conception of the law."

The three main arguments for originalism Rappaport identifies are: "1. Originalism as an interpretive theory (the most accurate meaning of the original document); 2. Originalism as a normative theory (the most normatively desirable interpretation of the Constitution); and 3. Originalism as positivism (the original meaning is the law)." Later in the post, Rappaport links "the positivist theory" to a theory that relies on a "rule of recognition." This linkage makes clear that the third kind of argument in Rappaport's taxonomy really is "positivism" rather than simply about the original meaning of the Constitution being positive law. This distinction is important because positivism need not be the only game in town when it comes to jurisprudential frameworks for (1) understanding the Constitution as positive law, or (2) underwriting a positive-law-based argument for some form of constitutional originalism. 

In particular, it seems to me that classical natural law jurisprudence has the potential to provide a powerful set of arguments for something like what Steve Sachs has recently (and aptly) called "original-law originalism." To be clear, I do not contend that classical natural law jurisprudence on its own does (or can) prescribe anything nearly as specific as, say, original-law originalism. The idea instead is that classical natural law jurisprudence may be able to explain the kind of positive law that the Constitution is in a way that supports original-law originalism as a jurisprudentially superior approach to rival theories of constitutional interpretation. 

This post is but a stab at a start. Whether to continue this inquiry and how far to take it will depend on how well arguments that I have not yet worked out actually do work out. (For earlier analysis and discussion of some issues that I may touch on, see this exchange between Robert George and James Fleming published in 2001 in the Fordham Law Review: George essay, Fleming critique, George reply, Fleming surreply, additional comments by George).

A good place to begin is classical natural law theory's account of the law's authority. Finnis writes:

Natural law theory's central strategy for explaining the law's authority points to the under-determinacy (far short of sheer indeterminacy) of most if not all of practical reason's requirements in the field of open-ended (not merely technological) self-determination by individuals and societies. Indeed, the more benevolent and intelligent people are, the more they will come up with good but incompatible (non-compossible) schemes of social coordination (including always the 'negative' coordination of mutual forbearances) at the political level--property, currency, defence, legal procedure, and so forth. Unanimity on the merits of particular schemes being thus practically unavailable, but coordination around some scheme(s) being required for common good (justice, peace, welfare), these good people have sufficient reason to acknowledge authority, that is, an accepted and acceptable procedure for selecting particular schemes of coordination with which, once they are so selected, each member of the community is morally obligated to cooperate precisely because they have been selected--that is, precisely as legally obligatory for the morally decent conscience. (CWJF IV.5.114-14)

Situating the Constitution of the United States within this account, the moral obligatoriness of the Constitution takes the form of legal obligation to cooperate with the Constitution as the posited scheme of coordination for serving the common good.

(Note: References to the Collected Works of John Finnis will take the form "CWJF Volume.Chapter.Page(s).)