History of the Greek alphabet retained the sound. A symbol based on the left-hand half ( ├ ) of the letter Η was therefore sometimes used to indicate the presence of where necessary, and its absence was indicated by a symbol based on the right half. During the classical period, ΕΙ came to be pronounced and ΟΥ came to be pronounced , Υ having meanwhile moved to . By about 200 BC, a system of diacritical marks was invented, representing the tone accents in use in Ancient Greek. This also helped to indicate the length of the vowels Α, Ι, and Υ in certain cases
History of the Greek alphabet Greek. Since the names of the letters "’āleph" and "hē" were pronounced and by the Greeks, with initial vowels due to the silent gutturals (the disambiguation "e psilon" "narrow e" came later), the acrophonic principle was retained for vowels as well as consonants by using them for the Greek vowel sounds and . Only the letter "‘ayin" for necessitated a change of name ("o", later "o micron"). Phoenician also had an "emphatic" consonant, "ṭēth", which did not exist in Greek. However, Greek had an aspiration distinction that Phoenician lacked, and used ṭēth for the aspirated . The Phoenician consonants "kaph"