 Grimm's law

Grimm's law (also known as the First Germanic Sound Shift) is a set of statements first systematically put forward by Jacob Grimm but first remarked upon by Rasmus Rask describing the 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, fricatives and the stop consonants of certain other centum Indo-European languages (Grimm used mostly Latin and Greek for illustration).