 Accordingly, it is mental states which are to be regarded as the referents of both psychological and physical terms. More precisely, Feigl assumes that, in the case of psychological terms, evidence is derived from (direct) knowledge by acquaintance, whereas in the case of physical (neurophysiological) terms evidence is derived from (indirect) knowledge by description (see Feigl 1967, p. 94). Yet, the referent is in both cases the same, so that we have a relation of ‘referential identity,’ as in the context of Gottlob Frege’s example of the terms ‘morning star’ and ‘evening star’ that differ in sense (Sinn), but not in reference (Bedeutung), which in both cases is identical, namely Venus (see, for this analogy, Feigl 1981, pp. 346–347). Consequently, we have two kinds of evidence for one and the same type of events. It is for this reason that Feigl’s identity theory is committed to a dualism at the evidential basis. Or, as Feigl puts it in “The ‘Mental’ and the ‘Physical’”: