History

Abstract

Distinguishing the observable from the unobservable is clearly important to an empiricist philosophy of science. The role of the distinction is no more clearly put than by the logical positivists. As presented by Carnap, the positivists’ position associates scientific meaningfulness with observability, and the association is carried out in terms of the language of science. Sentences are to be regarded as scientifically meaningful only if the constituent predicates can be linked to observational predicates, or are themselves observational predicates. (Carnap’s phrase is “observable predicates” rather than observational predicates as used here. The latter expression is preferable in light of an important distinction between entities which are observable or not, and terms, which are observational or not. The details and impact of this distinction will be presented in their historical place.) Carnap spends much of his time in clarifying the nature of the link between observational predicates and the terms of meaningful sentences, but for appreciating his conception of the observational-nonobservational distinction, it is more appropriate here to expand on his idea of an observational predicate.