compensatory lengthening

The result of contraction and “compensatory lengthening” was not ει and ου as in Attic and Ionic, but η and ω: ἦμεν infinitive = εἶναι from *esmen; gen. sing. of o-stems in ω: θεῶ, acc. pl. in -ως: θεώς; dy was represented by δδ, not ζ, as in Attic-Ionic; μύσιδδε = μύθιζε.

The sonant n appears in Brythonic as an, whereas in Goidelic the nasal disappears before k, t with compensatory lengthening of the vowel, e.g.

Similarly b, d, g disappear in Goidelic when standing after a vowel and preceding l, r, n with compensatory lengthening of the vowel, but in Welsh they produce a vowel forming a diphthong with the preceding vowel, e.g.

So in many cases there is a choice between compensatory lengthening and compensatory pause.

This was lost before -an of the infinitive, contraction and compensatory lengthening being the result.