Primitive Adûnaic had only two diphthongs: [ai] and [au] (SD/422). These diphthongs could be produced by various processes: a-fortification, the disappearance of consonants ([ʔ], [ɣ], [w], [j]) between vowels, or when the semi-vowels [w] and [j] became [u] and [i] before consonants and finally. When phonetic developments put [u] and [i] into contact with a following vowel, the result was not a diphthong, and the vowels were later separated when the glide consonant [w] or [j] was inserted between [u] or [i] and a following distinct vowel.