Definition of a vowel letter:
Vowel letters correspond to speech sounds, which are articulated with an open vocal tract and minimal constriction of the airflow by lips, throat or tongue.
In the English alphabet, the vowel letters are A, E, I, O, and U. The letter Y is sometimes considered a vowel when it represents a vowel sound (e.g.: happy).
Even though there are only five main vowel letters, they appear in most words and form the foundation of the English language.
Additionally, one can distinguish between long and short vowel sounds. Short vowels are often found in shorter words (e.g.: big, wet), while long vowels often occur in words with more than one vowel letter (e.g.: hope). There are a lot of silent vowels as well.
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