 Carnap’s paper (1950 [1956]) considers a variety of linguistic frameworks, such as those for: observable things (i.e., the spatiotemporally ordered system of observable things and events), natural numbers and integers, propositions, thing properties, rational and real numbers, and spatiotemporal coordinate systems. Each framework is established by developing a language that typically includes expressions for one or more kinds of entities in question, expressions for properties of the entities in question (including a general category term for each kind of entity in question), and variables ranging over those entities. Thus, a framework for the system of observable things has expressions that denote such things (‘the Earth’, ‘the Eiffel Tower’, etc.), expressions for properties of such things (‘planet’, ‘made of metal’, etc.), and variables ranging over observables. The framework for natural numbers has expressions that denote them (‘0’, ‘2+5’), expressions for properties of the numbers (‘prime’, ‘odd’), including the general category term ‘number’), and variables ranging over numbers.