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Grimm's law is a sound law that states that Proto-Indo-European voiceless stops (such as /p/, /t/, and /k/) became voiced stops (such as /b/, /d/, and /g/) in Germanic languages. It was first noticed by Jacob Grimm in 1822, and is named after him. Grimm's law is one of the most important sound laws in the history of Indo-European linguistics, and has helped to reconstruct the Proto-Indo-European language.