Lachmann's law is a somewhat disputed phonological sound law for Latin named after German Indo-Europeanist Karl Lachmann who first formulated it in 1850. According to it, vowels in Latin lengthen before Proto-Indo-European voiced stops which are followed by another (unvoiced) stop.
Examples PIE 'led' > (cf. short vowel in Ancient Greek ) PIE 'fortified' > (cf. short vowel in Sanskrit ) PIE 'covered' > (cf. short vowel in Ancient Greek )
Explanations According to Paul Kiparsky, Lachmann's law is an example of a sound law that affects deep phonological structure, not the surface result of phonological rules. In Proto-Indo-European, a voiced stop was already pronounced as voiceless before voiceless stops, as the assimilation by voicedness must have been operational in PIE ( → 'forced, made'). Lachmann's law, however, did not act upon the result of the assimilation, but on the deep structure > > .
Jay Jasanoff defends the Neogrammarian analysis of Lachmann's law as analogy followed by sound change. ( ⇒ * > * > ). Although this formulation ultimately derives from Ferdinand de Saussure, Jasanoff's formulation also explains problems such as: > * > - ⇒ *- > > * ⇒ * > * >
Because Lachmann's law also does not operate before PIE voiced aspirate stops, glottalic theory reinterprets the law as reflecting lengthening before glottalized stops, not voiced stops.
See also Glossary of sound laws in the Indo-European languages Winter's law, a similar law operating in Balto-Slavic
References
Sources
. PhD dissertation.
Further reading