p t k b d g f th h

corresponds point for point to the Sanskrit series: 

b d g bh dh gh p t k

The relation between phonetic pattern and individual sound is roughly parallel to that which obtains between the morphologic type of a language and one of its specific morphological features.  Both phonetic pattern and fundamental type are exceedingly conservative, all superficial appearances to the contrary notwithstanding.  Which is more so we cannot say.  I suspect that they hang together in a way that we cannot at present quite understand.

If all the phonetic changes brought about by the phonetic drift were allowed to stand, it is probable that most languages would present such irregularities of morphological contour as to lose touch with their formal ground-plan.  Sound changes work mechanically.  Hence they are likely to affect a whole morphological group here—­this does not matter—­, only part of a morphological group there—­and this may be disturbing.  Thus, the old Anglo-Saxon paradigm: 

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.