Editing Verner's law (section)

== Problem ==
A seminal insight into how the Germanic languages diverged from their [[Proto-Indo-European language|Indo-European]] ancestor had been established in the early nineteenth century, and had been formulated as [[Grimm's law]]. Amongst other things, Grimm's law described how the [[Proto-Indo-European language|Proto-Indo-European]] [[voiceless stop]]s ''{{PIE|*p}}'', ''{{PIE|*t}}'', ''{{PIE|*k}}'', and {{lang|gem-x-proto|*kʷ}}  regularly changed into Proto-Germanic {{lang|gem-x-proto|*f}} ([[voiceless bilabial fricative|bilabial fricative]] {{IPA|[ɸ]}}), {{lang|gem-x-proto|*þ}} ([[voiceless dental fricative|dental fricative]] {{IPA|[θ]}}), {{lang|gem-x-proto|*h}} ([[voiceless velar fricative|velar fricative]] {{IPA|[x]}}), and {{lang|gem-x-proto|*hʷ}} ([[voiceless labio-velar fricative|labio-velar fricative]] {{IPA|[xw]}}).{{sfn|Fulk|2018|p=102}}

However, there appeared to be a large set of words in which the agreement of [[Latin]], [[Greek language|Greek]], [[Sanskrit language|Sanskrit]], [[Baltic languages|Baltic]], [[Slavic languages|Slavic]] etc. guaranteed Proto-Indo-European ''{{PIE|*p}}'', ''{{PIE|*t}}'' or ''{{PIE|*k}}'', and yet the Germanic [[reflex (linguistics)|reflex]] was not the expected, unvoiced fricatives {{lang|gem-x-proto|*f}}, {{lang|gem-x-proto|*þ}}, {{lang|gem-x-proto|*h}}, {{lang|gem-x-proto|*hʷ}}  but rather their voiced counterparts {{lang|gem-x-proto|*β}}, {{lang|gem-x-proto|*ð}}, {{lang|gem-x-proto|*ɣ}}, {{lang|gem-x-proto|*ɣʷ}}. A similar problem obtained with Proto-Indo-European {{lang|gem-x-proto|*s}}, which sometimes appeared as Proto-Germanic {{lang|gem-x-proto|*z}}.{{sfn|Fulk|2018|p=107-8}}

At first, irregularities did not cause concern for scholars since there were many examples of the regular outcome. Increasingly, however, it became the ambition of linguists like the [[Neogrammarian]]s to formulate general and exceptionless rules of sound change that would account for all the data (or as close to all the data as possible), not merely for a well-behaved subset of it.

One classic example of Proto-Indo-European ''{{PIE|*t}}'' → Proto-Germanic {{lang|gem-x-proto|*ð}} is the word for 'father'. Proto-Indo-European {{wikt-lang|ine-x-proto|*ph₂tḗr}} (here, the [[Macron (diacritic)|macron]] marks [[vowel length]]) → Proto-Germanic {{lang|gem-x-proto|faðēr}} (instead of expected {{lang|gem-x-proto|faþēr}}).{{sfn|Fulk|2018|p=107-8}} In the structurally similar family term {{wikt-lang|ine-x-proto|*bʰréh₂tēr}} 'brother', Proto-Indo-European ''{{PIE|*t}}'' did indeed develop as predicted by Grimm's Law (Germanic {{wikt-lang|gem-x-proto|*brōþēr}}).{{sfn|Fulk|2018|p=106}} Even more curiously, scholars often found ''both'' {{lang|gem-x-proto|*þ}} and {{lang|gem-x-proto|*ð}} as reflexes of Proto-Indo-European ''{{PIE|*t}}'' in different forms of one and the same root, e.g. {{lang|gem-x-proto|*werþaną}} 'to turn', [[preterite]] third-person singular {{lang|gem-x-proto|*warþ}} 'he turned', but preterite third-person plural {{lang|gem-x-proto|*wurðun}} and past participle {{lang|gem-x-proto|*wurðanaz}}.