Unitary theories of memory are hypotheses that attempt to unify mechanisms of short-term and long-term memory. One can find early contributions to unitary memory theories in the works of John McGeoch in the 1930s and Benton Underwood, Geoffrey Keppel, and Arthur Melton in the 1950s and 1960s. Robert Crowder argued against a separate short-term store starting in the late 1980s. James Nairne proposed one of the first unitary theories, which criticized Alan Baddeley's working memory model, which is the dominant theory of the functions of short-term memory. Other theories since Nairne have been proposed; they highlight alternative mechanisms that the working memory model initially overlooked.