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description of the regular correspondences in Indo-European languages formulated by Jacob Grimm in his Deutsche Grammatik (1819-37; "Germanic Grammar"); it pointed out prominent correlations between the Germanic and other Indo-European languages of Europe and western Asia. The law was a systematic and coherent formulation, well supported by examples, of patterns recognized as early as 1814 by the Danish philologist Rasmus Kristian Rask. It is important for historical linguistics because it clearly demonstrates the principle that sound change is a regular phenomenon and not a random process affecting only some words, as had been thought previously.