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_, _üe_ to _ü_), the diphthongizing of the old high vowels (English _i_ to _ei_ to _ai_; English and German _u_ to _ou_ to _au_; German _ü_ to _öü_ 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 _ö_, 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 _ü_-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.