The works of Paul K. Feyerabend, Norwood Russell Hanson and Thomas S. Kuhn have come to occupy a central place in the annals of contemporary philosophy of science. Some of their contemporaries,, tend to regard them as the vanguard of a new “revolutionary” intellectual movement. Reacting against the views of their positivist predecessors, they embrace and propagate the idea that “pervasive presuppositions” are fundamental to scientific investigations. Thus, Feyerabend thinks that, “... scientific theories are ways of looking at the world; (...) and their adoption affects our general beliefs and expectations, and thereby also our experiences and our conception of reality”. This is in stark contrast to the positivist view that the aim of science is the systematization of experience that exists independently of any scientific theories. This new view of scientific theories also involves a “radical” conception of the nature of theoretical change. Rejecting the positivist notion of any constant element through such change, Kuhn regards a basic theoretical change as a conceptual revolution and “wants to say that after a revolution scientists are responding to a different world”. Hanson uses the phrase ‘theory-loaded’ to give expression to a view of the semantic content of observation statements that follows from this general position. (shrink)