Answer: 

Cardinal vowels are ‘a set of reference vowels’ used by phoneticians to describe language sounds of language. They consist of 8 vowels classified by tongue position, tongue height, and lip rounding. These represent extreme tongue positions, and the system was organized by Daniel Jones in the 20th century, building on earlier work by phoneticians like Ellis and Bell.

Every person produces speech sounds uniquely, making it challenging to identify and classify vowel sounds due to variations in speaking styles. To address this issue, Daniel Jones, a British phonetician, introduced the concept of cardinal vowels. Cardinal vowels are a set of eight vowel sounds with specific acoustic qualities, tongue, and lip positions. They serve as reference points for describing and categorizing vowel sounds in any language and are represented in the International Phonetic Alphabet (IPA). Unlike consonants, vowels are produced without obstructions in the oral cavity, adding to the complexity of vowel analysis in speech.

Cardinal vowels are described based on tongue position, tongue axis (vertical and horizontal), and lip rounding. The tongue’s highest point is the hard palate, and the lowest is the front tongue surface, determining vowel height (high, middle, low) and position (front, central, back). Lip rounding (rounded, unrounded, neutral) is also considered; front vowels are unrounded, while back vowels are rounded.

There are eight cardinal vowels numbered CV1 to CV8. CV1 and CV5 are identified by articulatory positions, while the other six rely on acoustic characteristics.

CV1: The vowel sound CV1 is characterized by the tongue being raised as far forward and as high as possible, while the lips can be either widely spread or unrounded. 

CV2, CV3, and CV4 – represent front vowels selected for their acoustic properties to create a sequence bridging CV1 and CV5.

CV5: It is characterized by the lowest position of the back of the tongue and unrounded lips.

The vowels are equally spaced from one another in terms of their acoustic characteristics, and this uniform separation is referred to as “equidistance.”

CV 6, 7, and 8: It represents vowels produced at the back of the tongue, following the principle of maintaining acoustic equidistance within the back vowel series.

The primary distinction among cardinal vowels 1, 2, 3, 4, and 5 lies in the varying tongue positions.  Lip positions have minimal impact on vowel differences.