Grimm's Law

Grimm's law (also known as the First Germanic Sound Shift or the Rask's-Grimm's rule), named after Jacob Grimm, is a set of statements 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). As it is presently formulated, Grimm's law consists of three parts, which must be thought of as three consecutive phases in the sense of a chain shift:

1. Proto-Indo-European voiceless stops change into voiceless fricatives.
2. Proto-Indo-European voiced stops become voiceless stops.
3. Proto-Indo-European voiced aspirated stops become voiced stops or fricatives (as allophones).

The chain shift can be abstractly represented as:

bʰ → b → p → ɸ

dʰ → d → t → θ

gʰ → g → k → x

gʷʰ → gʷ → kʷ → xʷ

Here each sound moves one position to the right to take on its new sound value. Notice that the new sound value entails the loss of a feature at each of the three steps. First the aspiration feature is lost, then voice and finally stop leaving a continuant.

The voiced aspirated stops may have first become voiced fricatives before hardening to the voiced unaspirated stops "b", "d", and "g" under certain conditions; however, some linguists dispute this. See Proto-Germanic phonology.

Grimm's law was the first non-trivial systematic sound change to be discovered in linguistics; its formulation was a turning point in the development of linguistics, enabling the introduction of a rigorous methodology to historical linguistic research. The correspondences between Latin p and Germanic f was first noted by Friedrich von Schlegel in 1806. In 1818 Rasmus Christian Rask elaborated the set of correspondences to include other Indo-European languages such as Sanskrit and Greek, and the full range of consonants involved. In 1822 Jacob Grimm, the elder of the Brothers Grimm, in his book Deutsche Grammatik, formulated the law as a general rule (and extended to include standard German).