Cardinal vowels are a set of reference vowels used by phoneticians in describing the sounds of languages. For instance, the vowel of the English word "feet" can be described with reference to cardinal vowel 1, , which is the cardinal vowel closest to it.

Vowel sound produced when the tongue is in an extreme position, either front or back, high or low. The current system was systematised by Daniel Jones in the early 20th century, though the idea goes back to earlier phoneticians, notably Ellis and Bell.

It takes much practice and training from an expert to learn to produce the cardinal vowels accurately. Three of the cardinal vowels, [i], [ɑ] and [u] have articulatory definitions. [i] is produced with the tongue as far forward and as high in the mouth as is possible, with spread lips. [u] is produced with the tongue as far back and as high in the mouth as is possible, with pursed lips. This sound can be approximated by adoping the posture to whistle a very low note, or blow out a candle. [ɑ] is produced with the tongue as low and as far back in the mouth as possible. The other vowels are 'auditorily equidistant' between these three 'corner vowels', at four degrees of aperture or 'height': close (high tongue position), close-mid, open-mid, and open (low tongue position).

These degrees of aperture plus the front-back distinction define 8 reference points on a mixture of articulatory and auditory criteria. These eight vowels are known as the eight 'primary cardinal vowels', and vowels like these are common in the world's languages. The lip positions can be reversed with the lip position for the corresponding vowel on the opposite side of the front-back dimension, so that e.g. Cardinal 1 can be produced with the rounding for Cardinal 8, etc.; these are known as 'secondary cardinal vowels'. Sounds such as these are less common in the world's languages. Other vowel sounds are also recognised on the vowel chart of the International Phonetic Alphabet.

See also

• list of phonetics topics