You already know that vowels in the English alphabet are a, e, i, o, u, and sometimes y, while the rest of the letters are called consonants. But did you ever ask yourself why the letters were divided into two separate groups?

Basically, a vowel is a sound that is made with the mouth and throat not closing at any point. In contrast, a consonant is a sound that is made with the air stopping once or more during the vocalization. That means that at some point, the sound is stopped by your teeth, tongue, lips, or constriction of the vocal cords.

The difference explains why “y” is only “sometimes” a vowel. Depending on which word “y” is being used in, it can represent different sounds. In words like “myth” or “hymn,” the letter takes on a sound like a short “i” and the mouth and throat don’t close when the sound is made. However, in words like “beyond,” it acts as a bridge between the “e” and the “o,” and there is some partial closure, making “y” a consonant.

Another forgotten letter that has the same qualities as “y” is “w.” While “w” is almost always a consonant, it is considered a vowel at the end of words like “wow” or “how.” You can see for yourself when saying these words that your mouth doesn’t fully close while pronouncing the letter.

There are, of course, other differences between vowels and consonants. For instance, in English you can have vowels that are entire words, such as “a” or “I.” You won’t see a consonant that is a word by itself, however. Words in English need vowels to break up the sounds that consonants make. So, while every word has to have a vowel, not every word has to have a consonant.

There are strings of consonants that are sometimes written like full words, like “hmm.” However, these are just sounds rather than actual words. You will also find that most words in English won’t have more than three consonants in a row, because otherwise it gets to be too difficult for English-speakers to say it. There are exceptions, of course—take the word “strengths” for example, which has a string of five consonants (though it only has three consonant sounds in a row: ng, th, and s). In other languages, like Polish, long strings of consonants are more common.

Of course, there are also sounds made by consonants that can be repeated over and over without a vowel sound. If you were to repeat “z” over and over, like the sound of a buzzing bee, you would find that your mouth remains slightly open and the sound is seemingly unobstructed—so shouldn’t it fall under the “vowel” category? The letter “z,” along with the letter “s,” actually fall under a subcategory of consonants called “fricatives.” Fricatives are sounds you make by pushing air through a small gap in your teeth.

As you can see, the differences between vowels and consonants are more complex than you were probably taught in elementary school. It’s less about the letters and more about how your mouth moves when you’re saying them.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

• Why Do the British Pronounce “Z” as “Zed”?
• The Differences Between British and American English
• Mozart and the Alphabet Song
• “Ye” in Names Like “Ye Olde Coffee Shoppe” Should Be Pronounced “The”, Not “Yee”
• The Origin of the English Alphabet

Bonus Facts:

• The word “vowel” comes from the Latin word vox, which means “voice.” The word “consonant” also has a Latin root, con sonare, which means “with sound.”
• There aren’t any words in the English language that have all five vowels in a row without any consonants in between. There is one word that has five vowels, with a repeated a, in a row: Rousseauian. It means “relating to the French philosopher Jean-Jacques Rousseau.” More commonly, “queuing” also has a lengthy string of vowels, but without an “a” or an “o.”
• There are also words in English which contain all five vowels (with consonants in between) in order. Some of these include facetious (“treating serious situations with inappropriate humour”), abstentious (“abstinent”), and caesious (“bluish or greyish green”).
• Ever wonder why “w” is pronounced “double-u” and not “double-v?” The Roman Latin alphabet was adapted to be used for Old English. Old English had a “w” sound, but back then the alphabet didn’t have a “w.” Instead, the “v” sound was pretty close, so words that required a “w” were often represented by a “v” instead. In the 7^th century, scribes started using “uu” to represent the “w” sound, which is how it got its name. However, printers used to use “vv” to represent the sound, which is how it got its shape.
• There are very few words in the English language that have two u’s in a row, and the only two that are used frequently are “vacuum” and “continuum.”  Nearly all of the “double u” words were adapted from Latin, such as “duumvir,” meaning “each of a pair of magistrates holding joint office in ancient Rome.” A few are adapted from other languages, such as “muumuu,” a loose dress that is traditionally worn in Hawaii.
• Just as you won’t find long strings of consonants in English, you also won’t find long strings of the same letter. No word in the English language contains more than a double letter, so you’ll never see three directly in a row. If a word seems to call for three, it will be hyphenated. For instance, the word for something without a shell is “shell-less” not “shellless.” In other cases, a letter is dropped. For instance, “seer” has only two e’s instead of the called-for “seeer” or “see-er.” The only exceptions to this rule are things like “shhh” or “brrr,” but these aren’t really words.