Primitive Irish: 1. Reduction of hiatus; 2. The u-infection of a; 3. The u-infection of penultimate syllables. Archaic Irish: 1. Reflexes of new final consonants; 2. Reduction of hiatus; 3. Coalescence of preverbs; 4. Compensatory lengthening. Early Old Irish: 1. Syncope of vowels in post-tonic syllables; 2. Composite forms; 3. Loss of intervocalic -w-; 4. The shift to rising diphthongs. Old Irish: 1. The short diphthongs; 2. The long diphthongs; 3. Reduction of hiatus. Conclusion.
Édouard Bachellery, in ÉtC 15 (1976-1978), pp. 741-746.