This study deals with the confusion of diphthongs /ow/ and /oj/ in the evolution of European Portuguese. Both diphthongs have different etymological basis, but in the ancient Portuguese they start to be confused.We analyzed selected words with these diphthongs in the diachronic corpus www.corpusdoportugues.org.
The results of this analysis showed that the final form of the word depends on its phonological structure: in the words with the final back vowel /o/ and /u/, the diphthong /ow/ predominates and in the words ending in central or central back vowel /ɐ/ or /ɨ/, a clearly preferred diphthong is /oj/.