During Donald Fiske's long career at the frontiers of psychological measurement, the paradigmatic dogma of logical positivism, with its definitional operationalism for theoretical terms, has come and gone. While always a participant in the exciting philosophy-of-science discussions as they affected psychology, Fiske has been consistently postpositivist in his research. I am thinking of his: (a) 1947 wartime (World War II) research on the validation of naval aviation selection tests, in which low-validity coefficients were explained as due, in part, to invalidity and unreliability in the criterion measures; (b) warnings about the biases due to individual differences in response fluency in Rorschach test scoring (Fiske & Baughman, 1953); (c) many studies of intraindividual variability between 1955 and 1974; and (d) subtle and creative preoccupation with invalidity in its many forms, which can be found in his individual articles and books: Measuring the Concepts of Personality (1971), Strategies for Personality Research (1978), and Problems with Language Imprecision (1981).