Winter's law, named after Werner Winter, who postulated it in 1978, is a proposed sound law operating on Balto-Slavicshort vowels */e/, */o/, */a/, */i/ and */u/ according to which they lengthen before unaspirated voiced stops, and that syllable gains rising, acute accent. Compare;
PIE *sed- "to sit" > Proto-Balto-Slavic *sēstej > Lithuanian sė́sti, OCS:wikt:сѣсти#Old Church Slavonic|sěsti.
PIE *h₂ebl- "apple" > Proto-Balto-Slavic *ābl- > standard Lithuanian ' and also dialectal forms of óbuolas and Samogitianóbulas, OCS :wikt:аблъко#Old Church Slavonic|ablъko, modern Serbo-Croatian ', Slovene ' etc.
Winter's law is supposed to showthe difference between the reflexes of PIE */b/, */d/, */g/, */gʷ/ in Balto-Slavic and PIE */bʰ/, */dʰ/, */gʰ/, */gʷʰ/. That shows that in relative chronology, Winter's law operated before PIE aspirated stops */bʰ/, */dʰ/, */gʰ/ merged with PIE plain voiced stops */b/, */d/, */g/ in Balto-Slavic. Secondarily, Winter's law is also supposed to show the difference between the reflexes of PIE *h₂e > */a/ and PIE */o/ which otherwise merged to */a/ in Balto-Slavic. When those vowels lengthen in accordance with Winter's law, old */a/ has lengthened into Balto-Slavic */ā/, and old */o/ has lengthened into Balto-Slavic */ō/. In later development, which represented Common Slavic innovation, the reflexes of Balto-Slavic */ā/ and */ō/ were merged, and they both result in OCS /a/. This also shows that Winter's law operated prior to the common Balto-Slavic change */o/ > */a/. The original formulation of Winter's law stated that the vowels regularly lengthened in front of PIE voiced stops in all environments. As much as there were numerous examples that supported this formulation, there were also many counterexamples, such as OCS stogъ "stack" < PIE *stógos, OCS ' "water" < PIE *. An adjustment of Winter's law, with the conclusion that it operates only on closed syllables, was proposed by Matasović in 1994. Matasović's revision of Winter's law has been used in the Lexikon der indogermanischen Verben. Other variations of the blocking mechanism for Winter's law have been proposed by Kortlandt, Shintani, Rasmussen, Dybo and Holst.
Criticism
Not all specialists in Balto-Slavic historical linguistics accept Winter's law. A study of counterexamples led Patri to conclude that there is no law at all. According to him, exceptions to the law create a too heterogeneous and voluminous set of data to allow any phonological generalization.
