Slavic Liquid Metathesis and Pleophony - Law of Open Syllables

During the Common Slavic period, a tendency known as the law of open syllables created the series of changes that completely eliminated closed syllables. This was evident in OCS, which had no closed syllables at all. Some of these changes include the monophthongization of diphthongs, loss of word-final consonants (e.g. 3rd person singular aorist OCS reče < *reket, OCS N sg of o-stems -ъ < *-us etc.), simplification of some medial consonant clusters (e.g. OCS tonǫti < *topnǫti etc.) and the formation of the nasal vowels *ǫ and *ę from *am/*an and *em/*en respectively.

Another change involved liquid consonants (R) *l or *r in closed-syllable *eRC and *aRC clusters, which were eliminated. The application of the law of open syllables for such clusters differed amongst the already differentiated Slavic dialects, but characteristically manifested in a number of dialects as the metathesis of liquid consonants, and is therefore called the liquid metathesis.