Attic had many diphthongs, all falling diphthongs with as the second semivocalic element, and either with a short or long first element. Diphthongs with a short first element are sometimes called "proper diphthongs", while diphthongs with a long first element are sometimes called "improper diphthongs." Whether they have a long or a short first element, all diphthongs count as two morae when applying the accent rules, like long vowels, except for in certain cases. Overall Attic and Koine show a pattern of monophthongization: they tend to change diphthongs to single vowels.