adigm:

Sing. Plur.
N. Ac. _fot_ _fet_ (older _foti_)
G. _fotes_ _fota_
D. _fet_ (older _foti_) _fotum_

could not long stand unmodified. The _o_--_e_ alternation was welcome in
so far as it roughly distinguished the singular from the plural. The
dative singular _fet_, however, though justified historically, was soon
felt to be an intrusive feature. The analogy of simpler and more
numerously represented paradigms created the form _fote_ (compare, e.g.,
_fisc_ "fish," dative singular _fisce_). _Fet_ as a dative becomes
obsolete. The singular now had _o_ throughout. But this very fact made
the genitive and dative _o_-forms of the plural seem out of place. The
nominative and accusative _fet_ was naturally far more frequently in use
than were the corresponding forms of the genitive and dative. These, in
the end, could not but follow the analogy of _fet_. At the very
beginning of the Middle English period, therefore, we find that the old
paradigm has yielded to a more regular one:

Sing. Plur.
N. Ac. *_fot_ *_fet_
G. *_fotes_ _fete_
D. _fote_ _feten_

The starred forms are the old nucleus around which the new paradigm is
built. The unstarred forms are not genealogical kin of their formal
prototypes. They are analogical replacements.

The history of the English language teems with such levelings or
extensions. _Elder_ and _eldest_ were at one time the only possible
comparative and superlative forms of _old_ (compare German _alt_,
_aelter_, _der aelteste_; the vowel following the _old-_, _alt-_ was
originally an _i_, which modified the quality of the stem vowel). The
general analogy of the vast majority of English adjectives, however, has
caused the replacement of the forms _elder_ and _eldest_ by the forms
with unmodified vowel, _older_ and _oldest_. _Elder_ and _eldest_
survive only as somewhat archaic terms for the older and oldest brother
or sister. This illustrates the tendency for words that are
psychologically disconnected from their etymological or formal group to
preserve traces of phonetic laws that have otherwise left no
recognizable trace or to preserve a vestige of a morphological process
that has long lost its vitality. A careful study of these survivals or
atrophied forms is not without value for the reconstruction of the
earlier history of a language or for suggestive hints as to it