The short vowels which are not at the very beginning of a word in written Mongolian may weak- ens in modern oral Mongolian,and even disappear,which is attributed by most scholars to the position of the ac- cent of the word.

Several rules of English vowel shortening are summed up; the nature and the regular pattern of long and short vowel alternation in the shortening rules are analysed; and the reason for the formation of shortening rules is discussed.

Based on the previous studies and the investigation of the document language materials and live materials of the modern Turkic languages,the article proves that there exists no short vowel e.