The position of the highest point of the tongue protrusion in the mouth can be classified according to the height of the tongue position and the difference between front and back.
The tongue position can be extended and shrunk, or raised and lowered (the opening can be large or small), and the lip shape can be round or not.
The lowering and raising of the tongue position has a certain relationship with the opening and closing of the mouth (i.e. the size of the opening degree): generally, the smaller the opening degree, the higher the tongue position, and the larger the opening degree, the lower the tongue position. Vowels can be divided into high vowels (that is, closed vowels, such as i, u), half high vowels (that is, half closed vowels, such as e, o), half low vowels (that is, half open vowels), low vowels (that is, open vowels), etc.
According to the front and back of the tongue position, it can be divided into front vowel, central vowel and back vowel.
