Ancient Greek dialects by the grammarians under the terms 'lexeis' or 'glôssai'. The dialects of Classical Antiquity are grouped slightly differently by various authorities. Pamphylian is a marginal dialect of Asia Minor and is sometimes left uncategorized. Mycenaean was deciphered only in 1952 and so is missing from the earlier schemes presented here: The Ancient Greek dialects differed mainly in vowels. Loss of intervocalic "s" and consonantal "i" and "w" from Proto-Greek brought two vowels together in hiatus, a circumstance often called a "collision of vowels". Over time, Greek speakers would change pronunciation to avoid such a collision, and the way that vowels
Ancient Greek phonology and this cluster underwent metathesis early in the Ancient Greek period. Metathesis is likely in this case; clusters of a voiced stop and , like , do not occur in Ancient Greek, since they change to by assimilation (see below), while clusters with the opposite order, like , pronounced , do occur. Ancient grammarians, such as Aristotle in his "Poetics" and Dionysius Thrax in his Art of Grammar, categorized letters () according to what speech sounds ( 'elements') they represented. They called the letters for vowels ('pronounceable', singular ); the letters for the nasals, liquids, and , and the letters