Grimm's law, principle of relationships in Indo-European languages, first formulated by Jakob Grimm in 1822 and a continuing subject of interest and investigation to 20th-century linguists. It shows that a process—the regular shifting of consonants in groups—took place once in the development of English and the other Low German languages and twice in German and the other High German languages. The first sound shift, affecting both English and German, was from the early phonetic positions documented in the ancient, or classical, Indo-European languages (Sanskrit, Greek, Latin) to those still evident in the Low German languages, including English; the second shift affected only the High German languages, e.g., standard German. Grimm's law shows that the classical voiceless stops ( k,t,p ) became voiceless aspirates ( h,th,f  ) in English and mediae ( h,d,f  ) in German, e.g., the initial sounds of Latin pater, English father, German Vater, and in the middle of Latin frater, English brother, German Bruder. It also shows that the classical unaspirated voiced stops ( g,d,b ) became voiceless stops ( k,t,p ) in English and voiceless aspirates ( kh,ts,f ) in German, e.g., the initial sounds of Latin decem, English ten, German zehn, and that the classical aspirated voiced stops ( gh,dh,bh ) became unaspirated voiced stops ( g,d,b ) in English and voiceless stops ( k,t,p ) in German, e.g., the initial sounds of Sanskrit dhar, English draw, German tragen.
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