As a PhD student that spent a lot of time reading and studying philosophy I came across the work of Paul Feyerabend, in particular his book "Against Method: Outline of an Anarchistic Theory of Knowledge" (1975).
As someone who at that time was already fascinated with the notion of rationality and its relation to method, I found Feyerabend to be exciting and inspring. He made a strong case against the belief that there is a "correct" method that we can trust when it comes to the production of scientific knowledge. He took a strong position against methods in any form or shape and advocated for an anarchistic stance when it came to methods for knowledge production.
Feyerabend developed a strong critique against all the typical claims and arguments supporting the primacy of a scientific method. He argues against correspondence, coherency, falsification, etc. Instead he argued for "anything goes". His main idea was that as soon as we define a method and define what constitute the correct way to go about doing things, we constrain both ourself and what we can achieve. A given method can only, with accompanying measures of success, lead to certain outcomes. In Feyerabends world that means that methods becomes both oppressive and limiting. When we are only allowed to examine the world in a given way, we reduce our possibilities to find new understandings and explanations that may be richer.
Feyerabend's work is relevant to me today not for his contribution to science studies and philosophy (even though I truly believe he is still more than relevant) but for the possibility to read his book as a wonderful examination and comment on design. Almost everything that Feyerabend discusses in his book is applicable to any discussion of design and particularly the design process and its relation to rationality and methods.
There has been a lot of (valid) critique of Feyerabend's philosophy. Feyerabend does not deal with a number of critical issues that emerges if his ideas are taken seriously. He is famous for almost ignoring the question of what makes a scientific result better than something else while his argument against methods is that they do not necessarily lead to "better" results. The core of this critique is the question how he can argue that something can lead to "better" results when there is no criteria for what constitutes better. To me this is a serious critique of his philosophy, even though I do think there are good answers to the criticism. Anyway, if we instead read Feyerabend as if he is writing about design, it may be easier to address the question of "progress" and "better" since design does not, as science, deal with the universal but with the particular. At the particular level we can always construct measure of success that are relevant and useful while not applicable when it comes to the universal. (This is a fairly long argument that I will not engage in now.)
My only problem with Feyerabend at the moment is that I have not read the book in any detail for a long time. After having gone back to it recently for other purposes, I do realize that it may be one of the most inspring philosophical books when it come to the question of the rationality of design practice and methods.