Vowels
English vowels are dvided into two majors types,
simple vowels (also called pure vowels or
monophthongs) and dipthongs.
Simple vowels don't show a noticeable change in quality.
Dipthongs are vowels that exhibit a change in quality
within a single syllable, English diphtongs show
changes in quality that are due to tongue movement away
from the initial vowel articulation.