Polskie zdania względne z wewnętrznym rzeczownikiem – wstępne rozpoznanie
troduced by a special relator który to, which in sentences bearing such clauses obligatorily agrees with the internal head. Such clauses have been hitherto overlooked in most syntactic descriptions of Polish. The inquiry is based on 291 citations obtained from the National Corpus of Polish, analysed for their semantic and syntactic features. The results show that double-headed relative clauses in Polish are marked as explicitly non-restrictive (as opposed to standard relative clauses). While identical internal and external heads need to be separated by a phrase governed by the external head, there is no such constraint on nonidentical internal heads. These may have not only nominal, but also clausal antecedents. In addition, non-identity of internal and external heads allows an introduction of subjective valuation (in the internal head) and a switch from object language to metalanguage or vice versa between the governing clause and the relative clause.