| Definition -
A hypothesis about the regularity of sound change, which states that a diachronic sound change affects — without exception and simultaneously — all words in its environment. Verner's law is a famous result derived from this hypothesis.
1. The Neogrammarian hypothesis was the first sound-change hypothesis to attempt to follow the principle of falsifiability. Nowadays, it is considered as more of a guiding principle than a fact, because numerous examples of sound changes that affect only a few words at first and then gradually spread to other words have been attested to.