EN
This study sets out to determine the differences in the phonological representation of RP English and Castilian Spanish diphthongs. The analysis brings to light the discrepancies in the criteria for classifying a vocalic cluster as a diphthong. A functional explanation for the differences between Spanish and English complex nuclei in provided in Beats-and-Binding framework (the model developed by Dziubalska-Kołaczyk 1995, 2002a, inter alia). The discussion also shows that English and Spanish glides phonologically differ by their ability/inability to propagate a n→B binding. The conclusion is that "diphthong" is an ad-hoc notion which denominates completely different phonological entities in English and Spanish. What follows, it could be successfully supplanted by the functional term complex beat.