to arising earlier in Proto-Germanic: PG > Late PG > OE > ModE "(I) thought". Anglo-Frisian brightening: Fronting of to (unless followed by a geminate, by a back vowel in the next syllable, or in certain other cases). Hence OE dæġ "day", plural dagas "days" (dialectal ModE "dawes"; compare ModE "dawn" < OE dagung ). This does not affect nasal . And since this is a back vowel, in a preceding syllable was prevented from being fronted as well. This created an alternation between the infinitive in *-aną and strong past participle in *-ana (< PG *anaz), where the former became -an in OE but the latter became *-ænæ > -en. Fronting of to (generally, unless followed). Final-syllable , and are lost. No attested West Germanic languages show any reflexes of these vowels. However, the way it affected the fronting of as described above shows that at least was retained into the separate history of Anglo-Frisian. Old English period This period is estimated to be c. AD 475–900. This includes changes from the split between Old English and Old Frisian (c. AD 475) up through historic early West Saxon of AD 900: Breaking of front vowels. Most generally, before , and + consonant (assumed to be velarized in these circumstances), but exact conditioning factors vary from vowel to vowel. Initial result was a falling diphthong ending in , but this was followed by diphthong height harmonization, producing short , , from short , , , long , , from long , , . Written ea, eo, io, where length is not distinguished graphically. Result in some dialects, for example Anglian, was back vowels rather than diphthongs. West Saxon ceald; but Anglian cald > ModE cold. Diphthong height harmonization: The height of one element of each diphthong is adjusted to match that of the other. > through this change, possibly through an intermediate stage . PG > OE > ModE stone. was first fronted to and then harmonized to . PG > OE "joy" (cf. ModE dream, ModG Traum). PG > OE > ModE death (Goth , ModG Tod). PG > OE > ModE eye (Goth , ModG Auge). is harmonized to . A-restoration: Short is backed to when a back vowel follows in the next syllable. This produces alternations such as OE dæġ "day", pl. dagas (cf. dialectal dawes "days"). Palatalization of velar consonants: were palatalized to in certain complex