One Roman letter covered two sounds
The Roman alphabet inherited a problem from Latin: I could stand for both a vowel and a consonant. As a vowel, it represented a sound like the “i” in machine. As a consonant, it often represented a sound closer to the “y” in yes—not the modern English sound of J in jam.
For a long time, readers worked out which sound was intended from the word. There was no need for a separate letter every time pronunciation differed.
A variant shape becomes useful
As handwriting styles changed, scribes sometimes gave I a longer or curved tail, especially at the end of a word or numeral. That hooked form—J—was initially a way of writing I, not a consistently separate letter with its own sound. Its shape made the two forms easier to distinguish on the page, but spelling practices varied across places and periods.
The decisive change was not simply drawing a new character. Writers increasingly used I and J to represent different sounds. That distinction took hold gradually, as scholars and printers made spelling more regular and readers encountered the same forms in books.
Why J comes near the end
Once J acquired a distinct identity, it had to find a place in an alphabet whose sequence was already familiar. It remained beside I, its older relative, rather than being inserted among the other letters according to its sound. That history is why the alphabet’s order preserves a visual family connection: J is a late-arriving letter that grew out of I, not an entirely new Roman character.
