History of the Greek alphabet only required one. The history here is complicated, but basically "sāmekh" dropped out in certain dialects, and was reused to represent in others, while usage for the sound varied between "ṣādē" and "šin". The letter now known as sigma took its name from "sāmekh" but its form from "šin", while the letter San, which occurred in a few dialects only, took its name from "šin" but its place in the alphabet from "ṣādē". A further Greek letter of uncertain origin, sampi, is found occasionally, and may represent an affricate, such as . For the special case of zeta, see Zeta
History of the alphabet All of the names of the letters of the Phoenician alphabet started with consonants, and these consonants were what the letters represented, something called the acrophonic principle. However, several Phoenician consonants were absent in Greek, and thus several letter names came to be pronounced with initial vowels. Since the start of the name of a letter was expected to be the sound of the letter (the acrophonic principle), in Greek these letters came to be used for vowels. For example, the Greeks had no glottal stop or voiced pharyngeal sounds, so the Phoenician letters "’alep" and "`ayin" became Greek "alpha"