The letter J was used as the swash letter I, used for the letter I at the end of Roman numerals when following another I, as in XXIIJ or xxiij instead of XXIII or xxiii for the Roman numeral representing 23. A distinctive usage emerged in Middle High German. Gian Giorgio Trissino (1478–1550) was the first to explicitly distinguish I and J as representing separate sounds, in his Ɛpistola del Trissino de le lettere nuωvamente aggiunte ne la lingua italiana (“Trissino’s epistle about the letters recently added in the Italian language”) of 1524. Originally, ‘I’ and ‘J’ were different shapes for the same letter, both equally representing /i/, /iː/, and /j/; but, Romance languages developed new sounds (from former /j/ and /ɡ/) that came to be represented as ‘I’ and ‘J’; therefore, English J, acquired from the French J, has a sound value quite different from /j/ (which represents the initial sound in the English language word “yet”).
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