Metaphysical

I am, by no means, a specialist - or even vaguely acquainted - with most positivist philosophy. Recently I read H.L.A. Hart's The Concept of Law in order to teach it to my legal studies students. Among other things, Hart is interested in destroying Austen's definition of law as the command of the sovereign backed up by coercive force. Part of Hart's problem with Austen's definition is the inclusion of the sovereign. Hart hates this idea - regardless of any other merits in Austen's definition, the inclusion of sovereignty is more or less enough to make it completely wrong. My problem, however, is that Hart's argument against sovereignty is anything but: it amounts to little more than saying, "Sovereignty is metaphysical." Apparently - for Hart at least, but I get the impression this is common for most positivists - saying something is metaphysical is enough to completely destroy another argument. I don't get it: why is calling sovereignty "metaphysical" a knock down argument that lets you move on to the next point? Put another way, even if sovereignty is "metaphysical" and has no concrete empirical referent - you never "see" sovereignty; you never "see" causality - the fact remains that sovereignty is ontologically real: people act as though it is there. Doesn't this amount to little but another form of the confusion regarding the reality of social constructed things? ("If they're socially constructed, that means they aren't real or imaginary.")

(Cross-posted to theoria.)