What are cardinal vowels?
Cardinal vowels are what is known as a set of reference vowels that are used by phoneticians to help them describe and classify the different sounds of languages. A cardinal vowel is a sound that is produced when the tongue is either at the extreme front, extreme back, extreme top or extreme bottom of the mouth. The system of cardinal vowels that is used to day was organised by Daniel Jones at the beginning of the 20th century, though the present organisation of cardinal vowels that we use can be seen to stretch back to the work of earlier phoneticians.
If you follow the top link below, you will be taken to a webpage with all of the cardinal vowels listed and a diagram of the mouth and where the tongue needs to be in order to pronounce them. Cardinal vowels are therefore very useful when it comes to working with new languages in order to map out the sounds and the vowels that are used in them.