Grimm's Law — sound change without exceptions, and the exception that deepened it

Grimm (1822): the PIE voiceless stops became Germanic fricatives, systematically — *p -> f (pater->father, ped->foot, piscis->fish), *t -> th (tres->three), *k -> h (cornu->horn, canis->hound, centum->hundred). The REGULARITY is the whole point: sound laws admit no exceptions (the Neogrammarian principle), which is exactly why the method PREDICTS rather than guesses. And the assay's own ethos appears here a century early: Grimm's law had stubborn apparent exceptions, and Verner (1875) chased them to a DEEPER rule — they depended on where PIE stress fell, and Verner's Law explained every one. An anomaly pursued honestly revealed a more fundamental law — the moat's discipline, in 19th-century philology. Empirical, discovered, predictive.