We cannot even begin to ferret out and discuss all the psychological problems that are concealed behind these bland tables.  Their general parallelism is obvious.  Indeed we might say that to-day the English and German forms resemble each other more than does either set the West Germanic prototypes from which each is independently derived.  Each table illustrates the tendency to reduction of unaccented syllables, the vocalic modification of the radical element under the influence of the following vowel, the rise in tongue position of the long middle vowels (English o to u, e to i; German o to uo to u, uee to ue), the diphthongizing of the old high vowels (English i to ei to ai; English and German u to ou to au; German ue to oeue to oi).  These dialectic parallels cannot be accidental.  They are rooted in a common, pre-dialectic drift.

Phonetic changes are “regular.”  All but one (English table, X.), and that as yet uncompleted, of the particular phonetic laws represented in our tables affect all examples of the sound in question or, if the phonetic change is conditional, all examples of the same sound that are analogously circumstanced.[159] An example of the first type of change is the passage in English of all old long i-vowels to diphthongal ai via ei.  The passage could hardly have been sudden or automatic, but it was rapid enough to prevent an irregularity of development due to cross drifts.  The second type of change is illustrated in the development of Anglo-Saxon long o to long e, via oe, under the influence of a following i.  In the first case we may say that au mechanically replaced long u, in the second that the old long o “split” into two sounds—­long o, eventually u, and long e, eventually i.  The former type of change did no violence to the old phonetic pattern, the formal distribution of sounds into groups; the latter type rearranged the pattern somewhat.  If neither of the two sounds into which an old one “splits” is a new sound, it means that there has been a phonetic leveling, that two groups of words, each with a distinct sound or sound combination, have fallen together into one group.  This kind of leveling is quite frequent in the history of language.  In English, for instance, we have seen that all the old long ue-vowels, after they had become unrounded, were indistinguishable from the mass of long i-vowels.  This meant that the long i-vowel became a more heavily weighted point of the phonetic pattern than before.  It is curious to observe how often languages have striven to drive originally distinct sounds into certain favorite positions, regardless of resulting confusions.[160] In Modern Greek, for instance, the vowel i is the historical resultant of no less than ten etymologically distinct vowels (long and short) and diphthongs of the classical speech of Athens.  There is, then, good evidence to show that there are general phonetic drifts toward particular sounds.