The IPA chart depicts vowels on the vowel quadrilateral with the shape and, in particular, the corners of the quadrilateral resembling the general relationship of the tongue position during the vowel productions [a], [i]. [o], [u]. Vowels can be described about advancement, tongue height, tenseness, rounding, length, and nasality. In relation, diphthongs reflect a single syllable that involves movement from one vowel to the next.