Scott Shapiro, a prominent defender of exclusive legal positivism—exclusivism—has intriguingly (re)introduced a logical principle, the endorsement and rejection of which he (I take it) supposes can helpfully distinguish exclusivism from its contrary, inclusive legal positivism—inclusivism. It is an intriguing thought that principles pitched at such a high level of abstraction as this could distinguish between the two versions of positivism. My aim will be to test whether this principle—and associated principles—can do such distinguishing work.