Where the diphthongs [ei] and [ou] developed at a later stage in Ilkorin, from the vocalization of [z] or of [g], these diphthongs developed into [ē] and [ou], as opposed to primitive ᴹ✶[ei] and ᴹ✶[ou] which became [ī] and [ū] respectively (PE19/25). The development is well-attested for [ou] > [au]: ᴹ✶kuʒnā > kogna > coun > Ilk. caun (Ety/KUƷ). This rule is more speculative in the case of [ei] > [ē], but can be deduced from examples like ᴹ✶ezdē > Ilk. Êd (EtyAC/EZDĒ). Helge Fauskanger suggested instead that this might simply be due to the lengthening of the original [e] rather than the development of a diphthong [ei] (AL-Doriathrin/méd).