2. Light tone is a special tone sandhi phenomenon in Chinese, which appears in most dialects and Putonghua in China. Light tone is generally not regarded as tone, because it has no fixed tone value.

3. There are only four tones in modern Chinese Pinyin: even tone, rising tone, rising tone and falling tone. In the phonetic sequence, many syllables often lose their original tone, but are read as a light and short tone. It is not the fifth tone besides the four tones, but a special tone sandhi of the four tones, which is physically manifested as the shortening of tone length and the weakening of tone intensity.