 The Pythagorean view shifts the problem of theoretical terms to the theory of meaning and reference for mathematical expressions. The question of how we are able to refer successfully to electrons is answered by the Pythagorean by pointing out that we are able to refer successfully to mathematical entities. Moreover, the Pythagorean explains, it is part of the notion of an electron that corresponding mathematical entities are connected to observable phenomena by means of axioms and inference rules. The empirical surplus of theoretical entities in comparison to “pure” mathematical entities is thus captured by axioms and inference rules that establish connections to empirical phenomena. Since mathematical entities do not, by themselves, have connections to observable phenomena, the question of truth and falsehood may not be put in a truth-conditional manner for those axioms that connect mathematical entities with phenomenal events (cf.  Section 4.2).  Carnap (1958), therefore, came to speak of postulates when referring to the axioms of a scientific theory.