 Returning to the digital, some commentators have questioned whether Goodman’s condition of (syntactic and semantic) finite differentiation is sufficient to distinguish the kind of representation in question (Haugeland 1981; Lewis 1971). John Haugeland, for example, argues that there can be differentiated schemes without the “copyability” feature that defines the practical significance of digital systems. Haugeland’s solution is to require the practical and not just the theoretical possibility of a system’s users determining type membership. In fact, however, Goodman himself would likely accept this modification. In a later work, Goodman explicitly states that finite differentiation must make it possible to determine type membership “by means available and appropriate to the given user of the given scheme” (Goodman and Elgin 1988: 125).