Grimm's law (also known as the First Germanic Sound Shift is a set of statements describing the inherited Proto-Indo-European (PIE) stops as they developed in Proto-Germanic in the 20BC"st 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.
Proto-Indo-European voiced stops become voiceless stops.
Proto-Indo-European voiced aspirated stops become voiced fricatives; ultimately, in most Germanic languages these voiced fricatives become voiced stops.
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.
