 In general, then, if by “psychologism” we mean simply the view that psychology is of direct relevance to certain areas of philosophy—as opposed to its (usually pejorative) usage in denoting the identification of psychological and normative or logical matters—there is ample backing for Goldman’s claim that “[p]sychologistic epistemology…is in the mainstream of historical epistemology” (1986:  6).[6]  It was Frege (in The Foundations of Arithmetic, 1884), and Husserl (in his “Prolegomena to Pure Logic”, in the Logical Investigations, 1900), with their trenchant critiques of psychologism in logic and mathematics, who were largely responsible for initiating the sharp turn away from this broadly naturalistic status quo (see Kusch 2014; see too Kitcher 1992, Goldman 1986, Kelly 2014, Anderson 2005, and Engel 1998). A key part of Frege’s and Husserl’s thinking here was that tying logic to psychology was incompatible with preserving its necessary character, and with its being knowable a priori. Following their lead, the logical positivists approached epistemology, as other areas, as a matter of a priori “rational reconstruction”, in Carnap’s (1928 [1967]) famous phrase. Such reconstruction “replace[d] rationally opaque processes with transparently rational definitions and inferences” (Richardson 2006: 682). Claims about ordinary objects were given “logical definitions” in a language that made reference only to experience (sense data); more complex such statements were defined in terms of simpler ones, and logical relations between them were made explicit. In none of this was the goal to be faithful to actual psychology.