Zero grade

In linguistics, the Indo-European ablaut (pronounced /ˈæblaʊt/) is a system of apophony (regular vowel variations) in the Proto-Indo-European language. All modern Indo-European languages have inherited the feature, though its prevalence and productivity strongly varies.

An example of ablaut in English is the strong verb sing, sang, sung and its related noun song, a paradigm inherited directly from the Proto-Indo-European stage of the language.

The term (from German ab- in the sense "down, reducing, gradated" + Laut "sound", thus literally meaning "sound gradation") was coined in the early nineteenth century by linguist Jacob Grimm. However, the phenomenon of the Indo-European ablaut itself was first recorded more than 2000 years earlier by the Sanskrit grammarians and was codified by Pāṇini in his Ashtadhyayi, where the terms guṇa and vṛddhi were used to describe the phenomena now known respectively as the full grade and lengthened grade.

In the context of European languages, the phenomenon was first described in the early 18th century by the Dutch linguist Lambert ten Kate, in his book Gemeenschap tussen de Gottische spraeke en de Nederduytsche ("Commonality between the Gothic language and Low German [Dutch]", 1710).

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