Halliday & Matthiessen (2014: 384):
Personal pronouns and proper names are alike in that, for both, the reference is typically unique. With pronouns, the referent is defined interpersonally, by the speech situation. With proper names it is defined experientially: there exists only one, at least in the relevant body of experience. In both cases, this means that typically there is no further specification; pronouns and proper names usually occur without any other elements of the nominal group. Sometimes they need further defining, like you in the back row, Henry the Eighth (this was how surnames started, as Qualifiers of personal names); and they may carry attitudinal Epithets, like poor Tom – cf. pretty little Polly Perkins of Paddington Green, which has both.