 There is a simple, intuitive and influential proposal how to relativize the theory-observation distinction in a sensible way: a term t is theoretical with respect to a theory T, or for short, a T-term if and only if it is introduced by the theory T at a certain stage in the history of science. O-terms, by contrast, are those that were antecedently available and understood before T was set forth (Lewis 1970; cf. Hempel 1973). This proposal draws the theory-observation distinction in an apparently sharp way by means of relativizing that distinction to a particular theory. Needless to say, the proposal is in line with the contextual theory of meaning.