Edward Sapir (18841939). Language: An Introduction to the Study of Speech. 1921.
to a höhith, hehith (later hehth) hangs; to dom doom, blod blood, and fod food corresponded the verbal derivatives dömian (later deman) to deem, blödian (later bledan) to bleed, and födian (later fedan) to feed. All this seems to point to the purely mechanical nature of the modification of o to ö to e. So many unrelated functions were ultimately served by the vocalic change that we cannot believe that it was motivated by any one of them.
The German facts are entirely analogous. Only later in the history of the language was the vocalic alternation made significant for number. And yet consider the following facts. The change of foti to föti antedated that of föti to föte, föt. This may be looked upon as a lucky accident, for if foti had become fote, fot before the -i had had the chance to exert a retroactive influence on the o, there would have been no difference between the singular and the plural. This would have been anomalous in Anglo-Saxon for a masculine noun. But was the sequence of phonetic changes an accident? Consider two further facts. All the Germanic languages were familiar with vocalic change as possessed of functional significance. Alternations like sing, sang, sung (Anglo-Saxon singan, sang, sungen) were ingrained in the linguistic consciousness. Further, the tendency toward the weakening of final syllables was very strong even then and had been manifesting itself in one way and another for centuries. I believe that these further facts help us to understand the actual sequence of phonetic changes. We may go so far as to say that the o (and u) could afford to stay the change to ö (and ü) until the destructive drift had advanced to the point where failure to modify the vowel would soon result in morphological embarrassment. At a certain