The Neogrammarian doctrine: sound laws admit no exception

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In the preface to the first volume of Morphologische Untersuchungen, Hermann Osthoff and Karl Brugmann set out the programme of the Leipzig school, whose central claim was that sound change proceeds without exception within a given dialect and period, with apparent exceptions to be explained by conditioning environments, analogy or borrowing. The doctrine followed directly from Verner's result of the previous year. It has been qualified extensively since — lexical diffusion and sociolinguistic variation both bear on it — but as a working assumption it remains what makes the comparative method a demonstration rather than an impression.

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