 Virtually all formal accounts of theoretical terms in fact assume that those phenomena which a theory T is meant to account for can be described in terms of expressions whose meaning does not depend on T. The counter-thesis that the meaning of putative observation terms depends on a quotidian or scientific theory, therefore, attacks a core doctrine in the logical empiricists’ and subsequent work on theoretical terms. A thorough discussion and assessment of theory-ladenness of observation in the works of the great historians of science is beyond the scope of this entry. Bird (2004), Bogen (2012) and Oberheim and Hoyningen-Huene (2009) are entries in the present encyclopedia that address, among other things, this issue. Schurz (2013: ch. 2.9) defines a criterion of the theory independence of observation in terms of an ostensive learning experiment, and shows how such a criterion helps answer the challenges of theory-ladenness of observation.