A number of the languages of Polynesia, including Tongan and Samoan, display a process whereby a pronominal argument of the main predicate of a clause appears to be realized as a preverbal 'second position' (2P) pronoun. All other arguments, if overt, are realized postverbally, the languages being rigidly predicate-initial. This paper examines the characteristics of these pronouns in Tongan arguing that in most cases they are best treated as distinct words in their own right (though often phonologically deficient) while in a handful of cases they are affixal material composed morphologically with a preceding preverbal Tense/Aspect Marker (TAM). Despite the fact that Tongan preverbal pronouns clearly do not appear in a typical argument position, standard approaches to 2P pronominal elements (e.g. 'clitic climbing' and 'prosodic inversion') do not seem naturally applicable to the Tongan data. The relation-based analysis provided here exploits a natural consequence of various potential definitions of 'subjecthood' within HPSG, treating the preverbal pronouns as the (unique) instantation of the valence feature SUBJ and correctly blocking the possibility of the pronoun appearing in true second position above the TAM when a clause-initial conjunction is present, except in particular specified circumstances. Thus the Tongan pronouns are not strict '2P' elements despite the fact that they most often appear in second position in a clause.