 Yet, the interpretation of theoretical terms by axioms of a scientific theory differs in several ways from that of a defined term by a definition. First, the introduction of theoretical terms may be joined with the introduction of another, theoretical domain of interpretation, in addition to the basic domain of interpretation in which observation terms are interpreted. Second, it must not be assumed that the interpretation of theoretical terms results in a unique determination of the extension of these terms. This is an implication of Carnap’s doctrine of partial interpretation (1958), as will become obvious by the end of this section. Third, axioms of a scientific theory are not conservative extensions of the observation language since they enable us to make predictions. Definitions, by contrast, must be conservative (cf. Gupta 2009). Taking these differences into account when observing the semantic similarities between definitions and Carnapian postulates suggests the following explanation: a set \(A(\TC)\) of axioms that interprets a set \(V_t\) of theoretical terms on the basis of a language \(L(V_o)\) imposes a constraint on the admissible, or intended, interpretations of the language \(L(V_o,V_t)\). An \(L(V_o,V_t)\) structure is admissible if and only if it (i) satisfies the axioms \(A(\TC)\) and (ii) extends the intended interpretation of \(L(V_o)\) to include an interpretation of the theoretical terms.