From the introduction to Paul Feyerabend’s Against Method:
This book proposes a thesis and draws consequences from it. The theses is: the events, procedures and results that constitute the sciences have no common structure, there are no elements that occur in every scientific investigation but are missing elsewhere. Concrete developments (such as the overthrow of steady state cosmologies and the discovery of the structure of DNA) have distinct features and we can often explain why and how these features led to success. But not every discovery can be accounted for in the same manner, and procedures that paid off in the past may create havoc when imposed on the future. Successful research does not obey general standards; it relies now on one trick, now on another; the moves that advance it and the standards that define what counts as an advance are not always known to the movers.
That sounds irrational, doesn’t it?