The four-sided figure (or vowel space) whose points are determined by the vowels with the articulatory positions of tongue high and front, tongue low and front, tongue low and back, and tongue low and high (see figure below). All other vowels are produced within or along the sides of the quadrilateral so defined.
Vowel space depicted along two dimensions: 1. high-low dimension along the vertical axis (representing the height of the tongue during vowel articulation and sometimes referred to as the close-open dimension). On an arbitrary basis, there are four points along this dimension (high, high-mid, low-mid, low). 2. Front-back dimension along the horizontal axis (representing the degree to which the mass of the tongue lies toward the front of the vowel space). Along this dimension, there are three arbitrary points (front, center, back). Combining the two dimensions, a vowel can be cross-classified in terms of its height (of articulation) in the vowel space and whether it is to the front, center or back of this space. The vowels are symbolized according to the notation system of the International Phonetic Association.
See Articulation, Vowels