Asno law

In historical linguistics, the asno law is a sound law in Proto-Indo-European where word-medial consonant clusters containing underlying *-Cmn- tend to lose one of the nasal consonants *m or *n. This sound change was first documented by Johannes Schmidt in 1895 and is named for the Avestan reflex 𐬀𐬯𐬥𐬋 asnō.^[1] The asno law, along with Stang's law, is one of Proto-Indo-European's manifestations of a phonotactic restriction against multiple adjacent sonorants in the coda of a syllable.^[2]

Affected affixes

The asno law is usually invoked to explain the disappearance of *-m- in the oblique case forms or thematic derivatives of animate-gender *-men- and *-mon- nouns, which have cases where a sequence *-mn- should appear. Thematic derivatives of neuter *-mn̥ nouns were also affected.

Phonological conditioning

The conditions under which the asno law is triggered remain controversial and unsettled. It is usually supposed to be triggered when the *-mn- sequence follows a consonant; if the *-mn- is preceded by a short vowel, the asno rule does not apply.

Byrd has *-Cmn- losing the *m if the preceding syllable was accented and the *n if the following syllable has the accent.^[1] This account is rejected by Tijmen Pronk.^[3] Alexander Nikolaev also rejects the post-tonic *n-loss part of this account but instead posits that asno rule applied to delete either one of *m or *n (more often *n) when the next syllable is accented. The asno law would also be generalized to thematized derivatives of any nasal-stem noun, including *r/n-heteroclitic nouns, where the base noun would lose the stem-final nasal in composition.^[4]

Dissimilatory loss of *-m- in *-mn- when the root contained a labial consonant has been used to explain many cases of the asno rule.^[5] Pronk posits this dissimilation as the sole mechanism of the asno rule.^[3]

Adiego alternatively proposes that the asno rule was conditioned not by the accent, as Byrd believes, but instead by the ablaut grade of the root; the zero grade would cause the deletion of *-m- but with other grades, the *-n- would be lost instead.^[2]