Kuhn planned to write a sequel to Structure, outlining this “evolutionary turn”, which he entitled Words and Worlds: An evolutionary view of scientific development. He began by proposing the notion of the lexicon to replace that of the paradigm. A lexicon comprises a scientific speciality’s collection of terms and concepts to chart the world taxonomically. So, when a scientific speciality evolves, its lexical terms change to reflect a new world and, as such, it is incommensurable with the parent lexicon. Instead of the incommensurability of paradigms entailing that there be no common meaning, Kuhn now argued that incommensurable paradigms had no common taxonomy. But a universal translating language, Kuhn argued, is not the solution to understanding these incommensurable terms; rather, the historian must enter the past world of science and become multilingual. Kuhn also changed incommensurability’s role to isolating lexicons of various scientific specialities, so that a new speciality can evolve from its parent as its own independent speciality. In sum, as scientific specialities evolve, their “words” capture more of the “worlds” open to scientific investigation.
Unfortunately, Kuhn did not complete Words and Worlds before he died. The question that arises is whether the sequel would have had a significant impact on contemporary philosophy of science, which is more pluralistic in its perspective than when Kuhn wrote Structure. Today’s philosophers of science have no need for a consensus framework, since each natural science is studied by its own philosophical sub-field. Kuhn’s evolutionary philosophy of science, however, might afford a possible candidate for reviving such a framework – but not in the conventional sense. Normally, the framework depends on a reduction of the non-physical sciences to the physical sciences. Physics is the model for what denotes a science; and the non-physical sciences must kowtow to physical terms and concepts. But this effort to provide a consensus framework for the sciences eventually fizzles out towards the end of the twentieth century.
Kuhn’s evolutionary philosophy of science, however, provides a possible consensus framework that outlines the relationships of the various natural sciences as they evolve and specialize. Thus it accounts for contemporary philosophy of science’s pluralistic stance, by clarifying the evolutionary relationships between the sciences – especially in terms of their common ancestry. Its goal is not to force the various sciences into a single scientific mould, such as the physical sciences, but to account for how these sciences progress like a branching tree of proliferating specialities. Although the full impact of Kuhn’s evolutionary philosophy of science may never be realized, the marriage between Structure and academic discourse remains sacrosanct, as is evident from the recent celebration of Structure’s golden anniversary – with no divorce imminent.