 Henry S. Leonard (1956) was the first to develop a free logic per se, though he used a defective definition of ‘E!’. Karel Lambert began his prolific series of contributions to the field in (1958), critiquing Leonard’s definition, and then coining the term “free logic” in (1960). The early systems of free logic were positive. Negative free logic was developed by Rolf Schock in a series of papers during the 1960s, culminating in (1968). Timothy Smiley suggested the idea of a neutral free logic in (1960), but the first thoroughgoing treatment appeared in Lehman 1994. Supervaluations were described in Mehlberg 1958, pp. 256–260, as a device for handling, not neutral free logic, but vagueness. But their formalization and application to free logic began with van Fraassen 1966, in which the term “supervaluation” was introduced. Dual-domain semantics were discussed in lectures by Lambert, Nuel Belnap and others as early as the late 1950s, but it appears that Church 1965 and Cocchiarella 1966 were the first published accounts.