Reduction of unstressed vowels in Proto-Frisian and the Germanic 'Auslautgesetze'

The quantitative reduction and loss of Proto-Germanic vowels during the transition from some form of Common North West Germanic to the attested ‘Old’ languages, such as Old English and Old Frisian, is a complicated process, interfering with morphological restructuring processes. Various reconstructions have been presented, the most extensive one by Boutkan (1995). Scrutiny of the Runic Frisian data, from the period ca. 500–800, shows that especially the apocope of PWGmc *-a and of *-u < PGmc *-ō should be positioned much later in the relative chronology than envisaged by Boutkan. The order that can be derived from the Runic Frisian data reflects a gradual loss of one mora, running in a cline from the least salient to the most salient vowel, which provides a phonetic rationale for the development. This gradual mora reduction can be dated to the period between ca. 500 and 700. This absolute dating can have implications for phonological processes in which root vowels interact with the quality or quantity of the vowel in the following syllable