Either in modern dialects or in Old Chinese in times of the PreQin, Two Han Dynasties, Wei and Jin and Northern and Southern Dynasties, Song Dynasty, Yuan Dynasty and Ming and Qing Dynasties, the front and back open vowels did not constitute contrastive phonemes, rather the configuration of vowel phonemes assumed a triangular shape. Nor the front and back open vowels were found contrastive in foreign transliterations of the middle ancient Chinese and in related languages. Therefore, in the middle ancient Chinese in times of the Sui and Tang Dynasties, Chinese front and back open vowels could not be contrastive but triangularshaped. In most modern dialects, most characters with secondclass open vowels in middle ancient Chinese contain no semi-vowel, and the major vowels belong to low vowels or sublow vowels. In some dialects, all secondclass open vowels contain no semivowels at all. So the secondclass open vowels could not contain semivowels in the middle ancient Chinese. It is supposed that some scholars in the old times might regard some firstclass vowels as the back open vowels ɑ or , the major of some secondclass vowels as a or the secondclass vowels should contain an e or the medial ɑ or . None of the abovementioned was wellgrounded. In fact, in middle ancient Chinese of the Sui and Tang Dynasties, the front and back open vowels differed only in phonetic value and showed no phonological difference like the case in other times of Chinese history. As a result, they offered no basis for classification. The open vowels a and ɑ (or ) belong to the same phoneme as the major of firstclass vowels. The secondclass vowels contain no semivowels, and their major vowels are sublow vowels, such as .

middle ancient Chinese; the firstclass vowel; the secondclass vowel; the major vowel; phonetic value