Flies or flys: What is the difference?

Pluralisation can be a tricky part of our language. As can knowing what the correct form of verb to use. One word that manages to cover both of these is fly.

Flies or flys?

The correct answer is almost always “flies”. “Flys” has nothing to do with flying an airplane or the bug called a fly. “Flys” is only correct when speaking of synonym nouns such as the zipper on the crotch, the “fly ball” in baseball, a type of old carriage, or the area over a stage.

In this article, I want to take a look at where the word comes from, what the rules of pluralising words that end in S are, what kind of word “flies” is and what tense it’s in.

Hopefully, at the end of this article, you will know more about the word “fly”, even if you won’t be able to do it yet.

Origin of the word “Flies”

Before we had the word “fly”, when we spoke Old English, we had the word “fleogan”. This word came from “Fleugan”, which is in a language called Proto-Germanic, which was a language that was spoken become English became a thing.

“Fleugan” comes from “Pleuk”, which is in Proto-Indo-European, one of the earliest languages that was spoken by humans. People still aren’t too sure what their civilisation was like.

If you ask me “Pleuk” sounds a bit like someone trying, but failing to fly.

Rules of “flies” or “flys”

Most of the time, when we wish to pluralise words, we simply add an S on the end. But when words end in Y, the rules are slightly different.

When the letter before the Y is a vowel, you follow the usual rule of just adding an S on the end. This is why we would say “I have two boys who both have stingrays.

It’s only when the letter before the Y is a consonant that the Y gets replaced by IES. “He often flies. He likes to explore the skies”.


Even though you should never say “flys”, there will be circumstances where you can say “fly’s”. This is to be used when talking about something that belongs to a fly. Even though flies don’t own things as we do, they still have possessions.

I might say “This fly’s wing looks odd”.

When you want to show that something is owned by a group of flies, you would add the apostrophe after the s. So I would say “If you leave your cake too long, it will become the flies’ cake”.

Hopefully, now, you have a better idea of how to pluralise words. And how the rules of plurals differ from the rules of possession.


What kind of word is it?

If I were to say “He flies through the sky”, I’m sure most of you will be able to tell me that “flies” is a verb.

A verb, by the way, is a doing word. “Flies” describes the action that someone is doing. But there’s more to it than that.

You would never say “I flies through the sky” or “They flies through the sky”. You would say “I fly through the sky” or “They fly through the sky.

When used as a verb, “flies” is written in the third person, singular.

What tense is it in?

The word “flies” is almost always written in the present simple. As I’m sure you’re aware, present tense refers to things that are happening at this moment or things that occur regularly.

When talking about fixed habits, we call it the present simple. If I say “Santa flies at night”, I’m not saying he is flying right now, just that’s what he does every year.

If Santa is in the sky when you’re reading this, you should say “Santa is flying in the sky”. And then go to bed- he won’t bring presents if you’re awake!

Flew, Flying, Fly

When you’re not talking in the present tense, you can use other terms.

When talking in the past tense, you would say “flew”. It doesn’t matter if you’re talking about yourself, someone else, or a group.

I flew, you flew, he flew, they flew, we flew.

When talking in the present continuous, you would say “flying”, as we’ve already established. I am flying, you are flying, he is flying, they are flying, we are flying.

“Fly” can either be used in the future tense or the present simple when talking about the person you’re talking to. ” I will fly to Germany tomorrow. But you fly all the time.”

Other Definitions of “fly”

Even though “fly” usually means travelling in the air, or a type of bug, there are other definitions of the word.

When used in the sentence “dissing your fly girl”, “fly” can either mean cool or good looking.

If something “isn’t going to fly with you”, you won’t be accepting it.

I often get super embarrassed when my “flies are undone”.

If an Australian gives something a “fly”, they are giving it an attempt.

“Fly” is also a type of old fashioned one-horse carriage. Interestingly, this type of fly gets pluralised by adding an S. “I saw two flys on the road today”.

Idioms associated with the word “flies”

English even has a few idioms that use the word “fly”. Most of these, you will have heard before.

  • When Pigs Fly. This is never going to happen.
  • Time flies when you’re having fun. When you’re enjoying yourself, time seems to pass quicker than it actually does.
  • Pass with flying colours. Pass easily, or with a large amount.
  • Fly on the wall—someone who does not want to be noticed and just wants to observe.


Whether we’re talking about the verb or the plural of the bug, you must always use “flies” and never “flies”.

I hope now, I have given you a better idea of how to pluralise words that end in Y. And you should also be clear about what type of word “flies” is, and what tense it’s in.

Time flies when you’re reading my articles!

Next time you need to use any words related to flying, you should be using the correct word, in the correct tense. Because if you don’t, you’ll have to read this article all over again.