Classical Adûnaic had only long diphthongs, the primitive short diphthongs [ai] and [au] having become the long vowels [ē] and [ō], respectively (SD/423). These long diphthongs were produced by the contact of two long vowels, and were always pronounced with the first element long and the second element short (SD/423). By the time of Classical Adûnaic, the long diphthongs were [āi], [āu], [ōi] and [ēu]; two older diphthongs [ēi] and [ōu] were reduced to [ē] and [ō] by the time of Classical Adûnaic (SD/424). Long diphthongs were usually seen as noun or verbal inflections, but could sometimes arise from the loss of primitive consonants (SD/424).