A
vowel diagram or
vowel chart is a schematic arrangement of the
vowels. Depending on the particular language being discussed, it can take the form of a triangle or a quadrilateral. Vertical position on the diagram denotes the
vowel closeness, with close vowels at the top of the diagram, and horizontal position denotes the
vowel backness, with front vowels at the left of the diagram. Vowels are unique in that their main features do not contain differences in voicing, manner, or place (articulators). Vowels differ only in the position of the tongue when voiced. The tongue moves vertically and horizontally within the oral cavity. Vowels are produced with at least a part of their
vocal tract obstructed.