A vowel is a speech sound you make with your mouth open and your voice flowing freely, without your tongue, teeth, or lips blocking the air. In English, the vowel letters are A, E, I, O, U, and sometimes Y. When you say “ah” at the doctor's office or sing a long note, you're making a vowel sound.

Try this: say the word “cat” very slowly. Notice how the “c” and “t” sounds involve your tongue or lips stopping or redirecting the air, but the “a” in the middle flows out smoothly? That's the vowel doing its job. Most English words need at least one vowel sound to be pronounceable. Without vowels, language would sound like a bunch of clicks and hisses strung together.

The letter Y acts as a vowel when it makes an “ee” sound (like in “happy”) or an “eye” sound (like in “fly”), but it's a consonant when it makes a “yuh” sound at the start of words like “yellow.”

Vowels are the backbone of syllables. A syllable is a single unit of sound in a word, and each syllable contains one vowel sound. The word “elephant” has three syllables (el-e-phant) and three vowel sounds, while “strength” has just one syllable and one vowel sound, even though it has more consonants.