High German Consonant Shift

The High German Consonant Shift or the Second German Consonant shift was a series of sound changes which separates the Upper High German dialects from other West Germanic languages such as Modern English, Dutch, and Low German. There are four major steps of this sound shift, and then there are other shifts which separate High German from other languages.

The Phases of the Shift

The 4 stages of the shift could be defined as follows:

1. Non-geminated voicless stops became fricatives,
2. Geminated and liquid-adjacent voiceless stops became affricates,
3. Voiced stops became voiceless stops, and finally
4. All interdental fricatives (/ð/ and /θ/) became the dental stop and/or Alveolar stop /d̻/ and /d/.
   

The last stage was shared by Low German and Dutch.

The shift occured in the period before Old High German existed, and in fact was the marker of Old High German.