is called compensatory lengthening, because the vowel length compensates for the loss of the consonant. The result of lengthening depended on dialect and time period. The table below shows all possible results: Wherever the digraphs correspond to original diphthongs they are called "genuine diphthongs", in all other cases, they are called "spurious diphthongs". Contraction In Attic, some cases of long vowels arose through contraction of adjacent short vowels where a consonant had been lost between them. came from contraction of , and from contraction of , , or . arose from and , from , and from and . Contractions involving diphthongs ending in resulted in the long diphthongs . Uncontracted forms are found in other dialects, such as in Ionic. Monophthongization The diphthongs became the long monophthongs and before the Classical period. Vowel raising and fronting In Archaic Greek, upsilon represented the back vowel . In Attic and Ionic, this vowel was fronted around the 6th or 7th century BC. It likely first became central , and then the front . For example, the onomatopoietic verb μῡκάομαι ("to moo") was archaically pronounced /muːkáomai̯/, but had become /myːkáomai̯/ in 5th century Attic. During the Classical period, – classically spelled – was raised to , and thus took up the empty space of the earlier phoneme. The fact that was never confused with indicates that was fronted before was raised. In late Koine Greek, was raised and merged with original . Attic–Ionic vowel shift In Attic and Ionic, the Proto-Greek long shifted to . This shift did not happen in the other dialects. Thus, some cases of Attic and Ionic correspond to Doric and Aeolic , and other cases correspond to Doric and Aeolic . Doric and Aeolic , Attic and Ionic ('mother') — compare Latin The vowel first shifted to , at which point it was distinct from Proto-Greek long , and then later and merged as . This is indicated by inscriptions in the Cyclades, which write Proto-Greek as , but the shifted as and new from compensatory lengthening as . In Attic, both and Proto-Greek were written as , but they merged to at the end of the 5th century BC. At this point, nouns in the masculine first declension were confused with third-declension nouns with stems in . The first-declension nouns had resulting from original , while the third-declension nouns had resulting from contraction of . Aeschines