As mentioned, for historical reasons these have traditionally been labeled as "front" vowels and "back" vowels. Indeed, in Romanized transcription of Mongolian, the vowels and are often conventionally rendered as and , while the vowels and are expressed as and (this is also the case in the nonphonological sections of this article). However, for modern Mongolian phonology, it seems more appropriate to instead characterize the two vowel-harmony groups by the dimension of tongue root position. There is also one neutral vowel, , not belonging to either group.