Grimm's law

Grimm's law (also known as the First Germanic Sound Shift or Rask's rule) is a set of statements named after Jacob Grimm describing the inherited Proto-Indo-European (PIE) stop consonants as they developed in Proto-Germanic (the common ancestor of the Germanic branch of the Indo-European family) in the 1st millennium BC. It establishes a set of regular correspondences between early Germanic stops and fricatives and the stop consonants of certain other centum Indo-European languages (Grimm used mostly Latin and Greek for illustration).

Grimm's law is the first non-trivial systematic sound change discovered, and though originally conceived of as a discovery in philology, it led to the creation of historical phonology as a separate discipline of historical linguistics. The correspondence between Latin p and Germanic f was first noted by Friedrich von Schlegel in 1806. In 1818, Rasmus Christian Rask extended the correspondences to other Indo-European languages, such as Sanskrit and Greek, and their full range of consonants involved. In 1822, Jacob Grimm, the elder of the Brothers Grimm, put forth the rule in his book Deutsche Grammatik, and extended it to include standard German.

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