In the Seoul dialect, the pronunciation of vowels is different according to the age of speakers, and so the vowel system is also different. Generally speaking, speakers over sixty years of age pronounce the vowel e in two ways;one is [*] and the other is [*:].The former [*] corresponds to the Middle Korean vowel e in a low or high accent and the latter [*:] to e in a low-high accent.These two vowels appear almost complementary to each other, i.e. [*] appears as a short vowel and [*] appears as a long vowel in most cases.In spite of that, I think that each of these two vowels falls to a different phoneme for the following reasons: (1)each vowel of the Seoul dialect, except [*] and [*], has an opposition of quantity in the word-initial syllable, but the sound value of a long vowel is not different from the correspnding short vowel, (2) usually, [*] appears as a long vowel and [*] as a short vowel, but there are a few examples where [*] appears as a short vowel and we can also find a few examples where [*] appears as a long vowel.Therefore I consider [*] and [*] correspond to different phonemes.Consequently, there are nine vowel phonemes, /i, e, e, a, a, o, u, i, a/;and each vowel has the opposition of quantity in the word-initial syllable in older people's pronunciation.The vowel system of speakers over sixty years of age is shown as  of table 1.
In contrast to older speakers, younger people have a very simple vowel system which consists of seven vowels, /i, e, a, o, u, i, A/. Thus we find the very interesting situation that speakers of the Seoul dialect have different vowel systems depending on their age group.This is the result of diachronic changes that have occurred over the last few decades.
I investigated eighteen informants who were native to the mid-town area of Seoul in 1988 and 1989 to clarify how vowels changed according to the age of speakers.The types of vowel systems shown at table 1 were found in the investigation.
The vowel changes according to the speakers'age groups can be pictured as shown at the table 5.
[*:] of groups  and  phonemically changed into [i:] in groups  and  for basic words which they learned orally in their childhood, but in literary words they borrowed [*:] from the older people's pronunciation.
[*:] was brought into the pronunciation of group  by the influence of the written language, i.e.spelling pronunciation, as language education began to follow a regulated curriculum from primary school, and additionally due to the analogical change in the verb conjugation which first occurs in this group. In group , [i:] and [*:] joins [*:] due to the increasing influence of the written language and in addition by the analogical change in verb conjugation.
In group , long vowels lose length and accordingly [*:] changes into [A], losing lip-rounding.
With respect to the front vowel opposition, group  and  have a clear distinction in initial syllables, but in non-initial syllables it hasalready disappeared as a rule except in morpheme-boundary position. Roughly speaking, most informants of groups that follow group  show unstable distinction even in initial syllables.
Considering the above-mentioned vowel change, it can be summarized that the change goes on very gradually in each age group because it occurs under the linguistic influence of elderly groups to restrain from the change and also being receded by interference of the written language and analogical change.Thus we see the reason why the different vowel systems can exist synchronically in the same speech community.