 Around this time, many of Feyerabend’s most important early papers were published. In them, under the influence of both Popper and Wittgenstein, Feyerabend initiated a vigourous critique of the then-orthodox philosophies of science provided by descendants of the Vienna Circle, “Logical Empiricist” thinkers such as Rudolph Carnap, Feigl, Nagel, and Hempel. This critique was conducted through a study of the relationship between observation and theory.