Theory-ladenness

In the philosophy of science, observations are said to be "theory-laden" when they are affected by the theoretical presuppositions held by the investigator. The thesis of theory-ladenness is most strongly associated with the late 1950s and early 1960s work of Norwood Russell Hanson, Thomas Kuhn, and Paul Feyerabend, and was probably first put forth (at least implicitly) by Pierre Duhem about 50 years earlier. Semantic theory-ladenness refers to the impact of theoretical assumptions on the meaning of observational terms while perceptual theory-ladenness refers to their impact on the perceptual experience itself. Theory-ladenness is also relevant for measurement outcomes: the data thus acquired may be said to be theory-laden since it is meaningless by itself unless interpreted as the outcome of the measurement processes involved. Theory-ladenness poses a problem for the confirmation of scientific theories since the observational evidence may already implicitly presuppose the thesis it is supposed to justify. This effect can present a challenge for reaching scientific consensus if the disagreeing parties make different observations due to their different theoretical backgrounds. Two forms of theory-ladenness should be kept separate: (a) The semantic form: the meaning of observational terms is partially determined by theoretical presuppositions; (b) The perceptual form: the theories held by the investigator, at a very basic cognitive level, impinge on the perceptions of the investigator. The former may be referred to as semantic and the latter as perceptual theory-ladenness. In a book showing the theory-ladenness of psychiatric evidences, Massimiliano Aragona (Il mito dei fatti, 2009) distinguished three forms of theory-ladenness. The "weak form" was already affirmed by Karl Popper (it is weak because he maintains the idea of theoretical progress directed to the truth of scientific theories). The "strong" form was sustained by Kuhn and Feyerabend, with their notion of incommensurability.