We are brainwashed early in our schooling to think that English has five vowels: A, E, I, O, U (and sometimes Y... in words like "fry" or "myth"). To linguists, though, a vowel isn't just a letter; it's a sound. Letters are merely meant (however sloppily) to represent sounds. By all accounts, English has many more than just five vowel sounds. Notice that the sound of A is completely different in the word "at" versus "ache" versus "about" versus "almond" versus "what." Most Americans even pronounce "ample" with an entirely distinct vowel. And all this under-the-surface diversity is represented simply by one letter! (So much for English spelling being logical or consistent.)
Depending upon one's exact accent of American English, there are really about 13 to 16 vowels. Depending on how we count, many British accents have even more vowels and English accents in South Wales perhaps more than 20!
The situation gets weirder because there's a subset of vowel sounds in English called "weak vowels." These appear only in unstressed syllables: all the ones except the one spelled A in the word "pronunciAtion." The kind of gold-standard weak vowel in English is a sound pronounced not too far back in the mouth, not too far forward, not too high towards the roof of the mouth, and not too low: a vowel in the very center of the vowel space. It is commonly symbolized by phoneticians as ə. In some accents of English, it's the sound of nearly every vowel in "pronunciation" --- prə.nən.ci.a.shən --- though saying the word precisely like this would sound a bit stilted to most American ears.
Here's a tricky question: does "pronunciation" rhyme with "shun" or with "shin"? The answer "neither" is also possible. Although I doubt how many Americans untrained in phonetics would be able to recognize it, most Americans certainly rhyme the word with "shin." (Not so much for Brits.)
Anoth
Every vowel letter --- what we learn in grade school -- can be used to represent the weak vowel: the A in "pita," the E in "delight," the I in "evil," the O in "summon," the U in "syrup," and even the Y in "anonymous."
Americans mostly have a phenomenon called the weak vowel merger, where