Abstract: What is the empirical content of a theory? If a theory is identified with one of its linguistic formulations, the only available answers allow for no non-trivial distinction between empirical and non-empirical content. The restriction of such a formulated theory to a narrow ‘observational’ vocabulary is not a description of the observable part of the world but a hobbled and hamstrung description of its entire domain, still with non-empirical implications. Viewing a theory as identified through the family of its models––the structures it makes available for modelling the phenomena––yields a new approach. The distinctions so made are illustrated with Newton's physics, absolute versus relative motion, nineteenth- century ether theory of electromagnetism, and quantum mechanics. A hermeneutic circle in the interpretation is noted, and the theory-independence of the observable/unobservable distinction maintained.

Keywords: absolute motion, empirical content, ether theory, hermeneutic circle, interpretation, model, Newton, observable, observational vocabulary, theory-independence, unobservable,