The letter J: origin, forms, sounds, and uses

In the Phoenician alphabet, the character yodh was used to render the semivowel [j], which can be described as both a palatal approximant and an unsyllabic [i]. When the Greeks developed the Greek alphabet from the Phoenician alphabet, they adopted the sign as an iota to write the vowel [i].

The Etruscans adopted the Greek sign, but used it not only to write the vowel [i], but also to write the homophonous semivowel [j] (just as they used the sign V for both the vowel [u] and the homophonous semivowel [w]). The Romans adopted the Etruscan usage unchanged.

In late antiquity, the semivowel [j] developed into a voiced affricate [dʒ]. From this arose the various sounds of the modern Romance languages. Thus, the Latin [j] (e.g. in iustus "just") corresponds to a [dʒ] (giusto [ˈdʒusto]) in modern Italian, to an [x] (justo [ˈxusto]) in modern Spanish, and to a [ʒ] (juste [ʒyst]) in modern French.

Although these considerable phonetic differences had already fully developed in the early Middle Ages, both sounds were still written with the same character until the early modern period, which could sometimes look like a J (as a majuscule), sometimes like an I (as a minuscule). The capitalis of the Romans did not know the graphic variant J yet. In the later uncial, the present form of the J with a small descender is recognizable. The consistent distinction between the letters I and J is said to have been first proposed in the 16th century by the French philosopher Pierre de la Ramée.

When the German language was written down towards the end of the first millennium AD, the letter I was used twice: On the one hand for the rendering of the unrounded closed front-tongue vowel [i], on the other hand for the rendering of the voiced palatal approximant [j]. Thus, the original Latin double usage was adopted, although the I in its use as a consonant letter in the Romance languages of the time meanwhile denoted another sound, a [dʒ].

Because the semivowel [j] persisted in German, the need for a distinction of the consonant letter J from the vowel letter I was less urgent than in other languages. This distinction was therefore not adopted in the writing of German texts until it was already established in other languages. Broken scripts did not distinguish between the majuscules I and J until around 1900. While only the use of the minuscules changed, it was not until after 1900 that broken types showed a distinguishable majuscule-J with an extended bow, as well as a compressed majuscule-I. As far as German texts were set in Antiqua, they already distinguished in the 19th century - just as today - between I/J and i/j.

To this day, there are still older scribes who use a J instead of the capital I (e.g. Jda, Jtalia). Even in sans-serif typefaces, a capital J is sometimes substituted for a capital I. One reason for this is that in such typefaces, the capital I and the lowercase L are often difficult or impossible to distinguish, especially when both letters are next to each other (for example, in Jll, Jller, Jlmenau, Jllustrierte as opposed to Ill, Iller, Ilmenau, Illustrierte).

"Since the Endstrichlosen play such a large role, one seems to think here and there that the I is insufficient and not infrequently substitutes for it the inverted J, that is, an inverted sound. If the I is followed by one or two l's, three naked vertical strokes are formed in the endless line. In a good script, however, these are not of the same size and thickness. At least the I is thicker by a trace. That must suffice."

- Jan Tschichold: Master Book of Writing

For some foreign words, there is both a German spelling with J, valid according to the new German orthography, and a technical spelling with I (e.g. iodine, next to iodine). In chemistry, the spelling with I is even preferred (analogous to citric acid).

Apart from proper names and abbreviations, no word ends in these letters according to spelling.