Cardinal vowels 2–4 and 6–7

[i ɑ u] are the easiest vowels to define in articulatory terms. The other CVs fit in between the cardinal vowels in auditorily equidistant steps. Articulatory descriptions of the cardinal vowels are impressionistic rather than factually correct: their definition is primarily an auditory and impressionistic one.

Between [i] and [ɑ], there are CVs 2–4, [e – ε – a]. They are all made with the tongue front in the mouth, and CV4, [a], is made with the tongue low in the mouth (and/or with an open jaw). They are ‘auditorily equidistant’ from each other, which means that the step from [i] to [e] sounds like the same sort of step as from [e] to [ε], and from [ε] to [a], etc. These vowels have lip postures that change from ‘close, spread’ for [i] to ‘neutral’ for [a].

Between [ɑ] and [u], there are two more cardinal vowels, [ɔ] and [o]. These vowels have accompanying lip rounding. [ɔ] has the most open rounding, and the amount of rounding and protrusion changes through [ɔ – o – u] to become more puckered and closer. As with the front series, the vowels [ɑ – ɔ – o – u] are auditorily equidistant from one another.

If there is more lip-rounding than to be expected according to the IPA, system, we can use the diacritic [,]; if there is less, then we can use the diacritic . For example [o] with the rounding of [u] can be transcribed . The diacritic is used for consonants that are accompanied by lip-rounding (as in e.g. RP , ‘saw’), but is also occasionally used to mark rounding at the end of a vowel, as a [w]-like off-glide into another sound, as in RP ‘go away’, .