Yu: The Letter for a Glide and a Vowel

Yu stands thirty third and writes the sequence of a glide followed by the vowel u. It carries no numeral value.

Old Church Slavonic wrote such sequences with letters of their own rather than with two signs, and yu is the member of that group that survived everywhere. It is present in every modern Cyrillic alphabet, unchanged in shape and in value, where its companions in the iotified series have mostly gone.

The reason it survived and they did not is that the sequences the others wrote either disappeared or were absorbed. The iotified e fell together with the plain e in most of the East Slavic area. The iotified a became the modern letter for ya. The iotified yus letters lost their nasal vowels and had nothing left to write. Yu had no such fate: the sequence it represents remained common and distinct, so the letter kept its job.

In the modern alphabets it does a second job as well. Because Cyrillic marks consonant softness on the following vowel, this letter after a consonant no longer writes a glide at all; it writes a plain u and says that the consonant before it is soft. The same letter therefore means one thing at the start of a word and another in the middle of one, which is a general property of the Cyrillic vowel letters and the point of the companion article.