The sameness-of-content criterion was criticized by David Lewis (1991, 40) as question-begging. Lewis suggests that the only alternatives for generating relations that Goodman allows are mereological, set-theoretical, or a combination of the two, and that only mereological generation passes the test. Unless one rejects set theory already, Lewis contends, one would not find the criterion plausible. There are, however, non-extensional mereological systems that violate the sameness-of-content criterion as well (see entry on mereology). Moreover, the sameness-of-content criterion may be understood as a version of  Ockham’s Razor, demanding not to multiply entities beyond necessity.