Vowel diagram

A representation of Daniel Jones's original cardinal vowel trapezium, which served as a basis for later vowel diagrams (though not the first of its kind; the original 1900 IPA chart had a somewhat similar form).

A vowel diagram or vowel chart is a schematic arrangement of vowels within a phonetic system (though also often used in phonemic descriptions). Vowels do not differ in place, manner, or voicing in the same way that consonants do. Instead, vowels are distinguished primarily based on their height (vertical position), backness (horizontal position), and roundedness (lip articulation). The degrees of height and backness may be used to describe either tongue articulation or acoustic quality, depending on the method of analysis. The former is the more traditional method, while the latter is the more modern method.

The vowel systems of all languages can be represented by vowel diagrams. Usually, there is a pattern of even distribution of vowel placement on the diagram, a phenomenon that is known as vowel dispersion. Most languages have a vowel system with three extreme points, forming a vowel triangle. Only 10% of languages, including English, have a vowel system with four extremes. Such a diagram is called a vowel quadrilateral or a vowel trapezium.

Alternatively, these shape-based terms are used to distinguish the method of analysis used for vowel diagrams: vowel triangles for diagrams typically based on § acoustics, and vowel quadrilaterals for diagrams typically based on § articulation. As such, languages which have three extremes may still be plotted within a vowel quadrilateral, and languages which have four extremes may still be represented with a vowel triangle.