Traditionally, Portuguese linguistics has acknowledged phonetic differences in vowel length conditioned by stress in Contemporary Standard European Portuguese (EP), yet has rarely addressed the possibility that underlying vowel length oppositions — not directly inherited from but analogous to those attested in Classical Latin and established through phonological developments in the 14th–15th centuries — may persist in the Contemporary language. In contrast, Makino (2006¹, 2006², 2007²) argued for the persistence of an underlying opposition in vowel length even in Contemporary EP, seeking to account for a range of phonological phenomena: the characteristic vowel alternations in open syllables preceding prepalatal and palatal consonants [ʃ ʒ ʎ ɲ]; the phonetic outcomes of vowel coalescence at the level of phrasal phonology; non-reduction in unstressed syllable of radical vowels of derived nouns and adjectives formed by suffixation to verbal radicals without intervening thematic vowels; and the absence of vowel reduction in unstressed syllables of derived words with negative implicatures. This theoretical study revisits this issue and offers a novel account of two phenomena: the absence of vowel quality reduction in nasal vowels in unstressed syllables, and the opposition [ɐ́ː] ≈ [áː] in the verb endings -amos and -ámos in the first-person plural of the present and preterite indicatives. The analysis is developed within the framework of Stratal Optimality Theory (Stratal OT), and employs a revised view of vowel feature geometry in which the traditional [±ATR] feature is reinterpreted as the terminal direction of a multistage tongue-height vector. Without introducing new phonetic data — except for a key pair of instrumental measurements that provide acoustic evidence for the underlying length distinction — this study offers a principled reinterpretation of phonological patterns that have previously been considered beyond the scope of systematic analysis.― ― ― The numbering of examples and figures is currently being revised to match that of the main text. We would be grateful if you could wait a little before downloading the file.