In Semitic, the letter was probably originally a pictogram for an arm with hand, derived from a similar hieroglyph that had the value of a voiced pharyngeal fricative (/ʕ/) in Egyptian, but was
reassigned to /j/ (as in English "yes") by Semites, because their word for "arm" began with that sound. This letter could also be used for the vowel sound /i/, the close front unrounded vowel, mainly in foreign words.
The Greeks adopted a form of this Phoenician yodh as their letter iota (Ι, ι). It stood for the vowel /i/, the same as in the Old Italic alphabet. In Latin (as in Modern Greek), it was also used for the consonant sound of /j/. The modern letter J was firstly a variation of this letter, and both were interchangeably used for both the vowel and the consonant, coming to be differentiated only in the 16th century.
In modern English, I represents different sounds, mainly a "long" diphthong /aɪ/, which developed from Middle English /iː/ after the Great Vowel Shift of the 15th century, as well as the "short", open /ɪ/ as in "bill". The dot over the lowercase 'i' is sometimes called a tittle. In the Turkish alphabet, dotted and dotless I are considered separate letters and both have upper-case (I, İ) and lowercase (ı, i) forms. Dotted İi denotes the normal /i/ sound as in most other languages, while dotless Iı denotes a close back unrounded vowel (/ɯ/).
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