Some reasons for talking about Popper’s “turns”.
First, for more effective teaching and criticism of Popper’s ideas. Popper has reformulated some of the traditional questions and people who come to his books after they have started in the mainstream will find that the landscape is unfamiliar. This happened to my father in the real world when he plunged into a dense thicket of bush on his farm and emerged on the same side. He was momentarily “lost” until he realized which way he was looking, then the landscape became familiar again. Readers may find that they are “lost” in Popper’s books until they realize that he has addressed different problems or reformulated versions of the traditional problems. For example he was not trying to justify beliefs, indeed he was not really concerned with beliefs at all. Nor was he trying to explicate terms and concepts.
His work can be seen as a program to explore the results when some old problems are addressed in some new ways. Agassi provided a hint to this process with his paper on the novelty of Popper’s philosophy of science (Agassi, 1968) where he described how major advances can be achieved when a “known but unappreciated solution to a given problem” is take seriously and the implications of the solution are unpacked.
One way to evaluate Popper’s achievement is to assess the progress that he made, given his own intentions and aspirations. It is essential to understand his program, that is, what he was trying to do, in order to make a helpful comparison with other programs.
Of course others may choose to continue with their own program rather than take up critical rationalism but in the light of the “compare and contrast” exercise that will be a rational choice, made after considering the alternatives, with reasons that can be discussed and subjected to criticism.
At present, too many books and articles on epistemology just address the justification of beliefs and do not acknowledge the existence of the alternative critical rationalist program.
Second, to identify some little-recognized shared concerns with other intellectual traditions and work in progress. Four of these: (1) the fallibillism of C S Peirce and John Dewey, (2) the focus on ignorance (what we do not know) of Firestein and (3) examination of the social and institutional context of science by Kitcher and (4) the various ways that research programs have been discussed (in advance of paradigm theory), for example Lovejoy’s historical study of key ideas, Collingwood’s alertness to metaphysical theories and more recently Kitcher’s concept of “scientific practice” including what he called “schemata” which are functionally equivalent to metaphysical research programs. (See the recent post on this topic)