The Greeks adopted a form of this Phoenician yodh as their letter iota (⟨Ι, ι⟩) to represent /i/, the same as in the Old Italic alphabet.

The modern letter 'j' originated as a variation of 'i', and both were used interchangeably for both the vowel and the consonant, coming to be differentiated only in the 16th century.

[2] In some sans serif typefaces, the uppercase ⟨I⟩ may be difficult to distinguish from the lowercase letter L, 'l', the vertical bar character '|', or the digit one '1'.

This pattern arose for basically the same reason that lowercase ⟨i⟩ acquired a dot: so it wouldn't get lost in manuscripts before the age of printing: The capitalized "I" first showed up about 1250 in the northern and midland dialects of England, according to the Chambers Dictionary of Etymology.

Chambers notes, however, that the capitalized form didn't become established in the south of England until the 1700s (although it appears sporadically before that time).

Capitalizing the pronoun, Chambers explains, made it more distinct, thus "avoiding misreading handwritten manuscripts.