PRONUNCIATION

Depending on the language we can have several intermediate tongue heights.

 Englishhas three heights: high, mid and low, whereas French has two intermediate tongue heightswith a total of four tongue heights: high, mid high, mid low and low.The part of the tongue involved in the production of a vowel can also be illustratedwith the examples above. 

If you say [i:] and then [u:] just after it, you almost have the feelingthat you are moving your tongue backwards. This is because [i:] is a front vowel, and [u:] isa back vowel, or in other words, the highest point in the pronunciation of [i:] is the front ofthe tongue, whereas the highest point in [u:] is the back of the tongue. 

Length

As you may have seen, there are two types of [i] sound in English placed in two
different positions. However for the purpose of description, what is relevant is not the
difference of position but that of the perceived length of the vowel. Thus it is said that [i:] is
a long vowel and [H] is a short one. The same is valid for [u:] / [T], [2:]/[?], [N:]/ [P].
Symbols for long vowels all have a colon.
Phonologically, one can establish the rule such as only long vowels may be the last
sound of a syllable, whereas short vowels are always followed by at least a consonant. If we
take away the final [t] from court, [kN:] is a possible syllable (core) whereas [kP] could not
possibly occur. (Exceptions from this are the three short vowels that occur in completely
unstressed syllables, [sHtH, HntT, swet?] city, into, sweater).
 Rounding
Vowels may also be different from each other with respect to rounding. If you
compare [i:] in [tRi:z] cheese with [u:] in [tRu:z] choose, you will see that not only is [i:] a
front vowel and [u:] a back vowel, but [i:] is also unrounded where [u:] is rounded. When
pronouncing [u:] your lips are rounded, but when pronouncing [i:] the corners of the mouth
are much further apart.