 The next milestone was the AGM model, so called after its three originators, Carlos Alchourrón, Peter Gärdenfors, and David Makinson (1985). Alchourrón and Makinson had previously cooperated in studies of changes in legal codes (Alchourrón and Makinson 1981, 1982). Gärdenfors’s early work was concerned with the connections between belief change and conditional sentences (Gärdenfors 1978, 1981). With combined forces the three wrote a paper that provided a new, much more general and versatile formal framework for studies of belief change. (On the history of their joint work, see Makinson 2003 and Gärdenfors 2011.) Since the paper was published in the Journal of Symbolic Logic in 1985, its major concepts and constructions have been the subject of significant elaboration and development. The AGM model and developments that have grown out of it still form the core of belief revision theory.