The absence of plural referring expressions from the predicate calculus forces quantification to function in the calculus in a way that is significantly different from the way it functions in natural language. In natural language, pluralities are introduced and specified by means of plural referring expressions; in the predicate calculus, a plurality, which is unspecified by the sentence, is introduced by presupposing a domain of discourse. In order to speak of pluralities natural language sentences presuppose no domain of discourse, in the technical sense in which this concept is used in predicate logic semantics. In natural language, the context directly determines the reference of the concepts used. Variables resemble plural referring expressions in some respects. The plural reference involved in a quantified sentence of the predicate calculus is introduced by the quantified construction itself, and not by any specific expression in it.