 On the other hand, there might be several mutually inconsistent schemes of principle, each consistent with the original set of norms. The interpreter would therefore have to choose from among these schemes on grounds other than consistency with institutional practice. Normally it would not be permissible, on this model, to add a principle to the original set of norms (or to rely upon it to generate more norms) just because it was attractive. Rather, the principle would have to bear a relation at least of consistency with some norm in the original set. But, in case that relation did not uniquely determine the principles in a scheme, the interpreter would have to choose without being able to ground the choice by appeal to the original set. He would have to choose on merit alone. (This is a consequence of the model that has attracted a lot of criticism. See Raz 1994: 223–6; Finnis 1987, 1992. For Dworkin’s protests that the distinction is merely heuristic, and should not be understood to mark two different dimensions of interpretation, see Dworkin 1982, 1986, 2006.)