Havlík's law is a Slavic rhythmic law dealing with the reduced vowels (known as jers or yers) in Proto-Slavic. The letter Yer or Jer ( Ъ, ъ) of the Cyrillic alphabet is known as the hard sign (твёрдый знак znak in the modern Proto-Slavic is the Proto-language from which Slavic languages later emerged It is named for the Czech scholar Antonín Havlík (1855-1925), who determined the pattern in 1889. Year 1889 ( MDCCCLXXXIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common While Havlík's law was a precursor to the loss of the jers, that process is part of the individual history of the various Slavic languages. Havlík's law was already in effect at the end of the Proto-Slavic period, and ended the era of open syllables, a major phonological feature of Proto-Slavic. A syllable ( Greek:) is a unit of organization for a sequence of speech sounds
The front and back jers come from the Proto-Indo-European short high vowels ĭ and ŭ, respectively. The letter Yer or Jer ( Ъ, ъ) of the Cyrillic alphabet is known as the hard sign (твёрдый знак znak in the modern As vowels, they played a role in the law of open syllables, which states that every syllable must end in a vowel.
Word-final jers, which were abundant—including in declensional patterns—were reduced in length to ultrashort, or "weak", variants. These weak jers were then often elided. Elision is the omission of one or more sounds (such as a Vowel, a Consonant, or a whole Syllable) in a word or phrase producing a result that is easier In words with multiple jers, the weak variants were not limited to word-final position.
Havlík's law describes the pattern in which weak and strong jers occur. Counting from the last jer in a word, the final jer is weak, the previous jer is strong, the previous jer is weak, etc. , until a full vowel is reached, and then the pattern is started again with a weak jer, then a strong jer, etc.