J[ohn ]W[atkins]: “Karl, you are dishonest. You hate criticism.”

K[arl ]R[aimund ]P[opper]: “You are dishonest. Your statement refers to my state of mind; it is irrefutable. Only dishonest people raise irrefutable criticism.”

Imre Lakatos, Letter to Paul Feyerabend, February 5, 1970, in Matteo Motterlini (ed.), For and Against Method: Including Lakatos’s Lectures on Scientific Method and the Lakatos-Feyerabend Correspondence, Chicago, 1999, p. 189