 Ramsey ([1929] 1931) assumes that there is but one domain of interpretation for all descriptive symbols. Carnap (1956, 1958), by contrast, distinguishes between a domain of interpretation for observational terms and another for theoretical terms. Notably, the latter domain contains exclusively mathematical entities. Ketland (2004) has emphasized the importance of distinguishing between an observational and a theoretical domain of interpretation. TC is a first-order sentence in Ramsey’s seminal article “Theories” ([1929] 1931). Carnap (1956; 1958), however, works with higher-order logic to allow for the formulation of mathematical propositions and concepts.