This generative phonological study brings together for the first time an exhaustive treatment of the Portuguese data relating to changes in vowel height and the several descriptive frameworks and distinctive feature systems available for their codification. A detailed acoustic phonetic analysis of the Portuguese vowel data is followed by a review of the history of confusion between secondary and primary tongue-body height. The author then argues for a set of Articulator Features’—an extension of the Chomsky and Halle ‘SPE’ distinctive feature system in which all SPE place-of-articulation features are replaced by strictly binary articulator-based features. This framework is then applied to the previously problematic Portuguese vowel-height data and is shown to be capable of both elegant and explanatory codification of the data. Finally, it is shown that these new explanatory rules render simple certain previous solutions on the basis of which it has been erroneously argued that vowel height in Portuguese is not binary.