From Choosing Elements to Choosing Concepts: The Evolution of Feferman’s Work in Model Theory

When Solomon Feferman began his research with Alfred Tarski in the early 1950s, model theory was still in process of becoming a distinct part of mathematical logic. Although Feferman’s doctoral thesis was not in model theory, his interests included model theory from the start, and he published a paper in the field roughly once every six years throughout his career. His earliest work in model theory is recognised in the name ‘Feferman-Vaught theorem’, which stems from some very detailed bare-hands work on sums and products of structures. During the 1960s and 1970s he worked on applications of many-sorted interpolation theorems, in particular to derive results relating implicit and explicit definability in various contexts. In the 1980s he edited with Jon Barwise a monumental collection of essays on ‘Model-theoretic logics’. In more recent papers he reflected on the conceptual basis of model theory from a historical point of view.