The most influential critique of the Logical Positivists’ analysis of scientific observation was posed by Paul Feyerabend in his classic essay, “Explanation, Reduction, and Empiricism”. Feyerabend countered the later Positivist conception with his so-called ‘Pragmatic Theory of Observation’ which was founded on two ideas. The first is that observation reports are ‘theory-laden’, in the sense that they are always interpreted in the light of the best current theory and are subject to reinterpretation when one theory succeeds another. Feyerabend traced the development of this idea in the early writings of the Positivists, especially Rudolf Carnap, in the classic discussion of protocol sentences. In that context, Feyerabend finds that the theory-ladenness of observation leads inexorably to the second idea of the Pragmatic Theory, that what counts as an observation report does not depend on either its empirical content or its logical form, but on its causal or pragmatic features.