Well, not to put too fine a point on it, notions of law were (and I suppose are still) evolving, and there are different degrees of "enforceability".
There was/is a concept of "natural law", as well as "laws of nature" and "laws of physics". Not "enforceable" in the common sense, of course, but they have their own methods for prevailing. "Common law", itself, shifts in "enforceability" as elements are forgotten, discovered, or precedents set. And some things are more powerful, enforceable, even, than "law" - customary laws, bonds of blood, oaths, and so forth.
But I shouldn't be too quick to underestimate the power of a widely accepted idea to compell normative behaviour, even if not "enforceable" in a legal sense.
Cheers - Howie