If you are unsure whether to write “flys” or “flies,” the correct choice in standard English is usually “flies.” But there is an important detail: fly has several meanings, and the correct form depends on whether you are using it as a noun or a verb.
For example, you write “The bird flies south” because flies is the third-person singular form of the verb fly. You also write “There are many flies in the kitchen” because flies is the plural of the noun fly. “Flys” is generally not the standard spelling for either of these uses.
This guide explains the difference between fly and flies, when the -y → -ies spelling rule applies, why flys is a common mistake, and how to choose the right form in everyday, academic, workplace, and professional writing.
Quick Answer: Flys or Flies?
“Flies” is the correct standard English spelling. “Flys” is normally incorrect.
- Fly → singular noun or base-form verb
- Flies → plural noun or third-person singular verb
- Flew → past tense of fly
- Flown → past participle of fly
- Flying → -ing form of fly
Examples
- Correct: A bird flies over the house.
- Correct: Several flies are near the window.
- Incorrect: A bird flys over the house.
- Incorrect: There are several flys in the room.
Memory tip: When fly becomes a plural noun or a third-person singular verb, the y changes to ies: fly → flies.
Oxford lists the noun plural as flies and gives the verb forms as fly, flies, flew, flown, and flying.
What Does “Fly” Mean?
The word fly can be a noun or a verb, and its meaning changes with its grammatical role.
As a noun, fly can mean a small flying insect:
A fly landed on the table.
The plural is flies:
Several flies landed on the food.
Oxford defines fly as a countable noun for a small flying insect and gives flies as its plural.
As a verb, fly means to move through the air, travel by aircraft, or operate an aircraft, among other meanings:
Birds fly south in winter.
We fly to London tomorrow.
Cambridge and Oxford both recognize these uses of fly.
Why this matters
Knowing whether fly is functioning as a noun or verb makes the spelling much easier to understand. In both of the common cases that produce flies, the standard spelling is the same.
Key takeaway: Fly is the base form; flies is used for a plural noun or a third-person singular present-tense verb.
Why Is It “Flies” and Not “Flys”?
The spelling follows a common English rule for words ending in consonant + y.
When a noun becomes plural, or when a verb takes the third-person singular -s, the y usually changes to i and -es is added.
So:
| Base word | Correct form | Use |
| fly | flies | plural noun |
| fly | flies | he/she/it verb |
| try | tries | plural/third-person verb form |
| carry | carries | third-person verb |
| study | studies | third-person verb |
| baby | babies | plural noun |
The important pattern is:
consonant + y → ies
So:
fly → flies
Compare this with words ending in a vowel + y
Not every word ending in y changes to ies.
For example:
- boy → boys
- day → days
- key → keys
- toy → toys
Here, the letter before y is a vowel.
That gives you a useful test:
Consonant + y → ies
Vowel + y → ys
Why it matters
This distinction helps prevent mistakes such as flys, boies, or studys.
Key takeaway: Don’t simply add -s to every word ending in y. Check the letter immediately before the y.
“Flies” as a Verb
One of the most common uses of flies is as the third-person singular present form of fly.
The pattern is:
- I fly
- You fly
- We fly
- They fly
- He flies
- She flies
- It flies
Oxford specifically lists he/she/it flies as the present simple form of fly.
Examples in everyday English
The bird flies over the garden.
My brother flies to Dubai for work.
The plane flies every morning.
A bee flies from flower to flower.
Examples in professional writing
The airline flies to several international destinations.
The aircraft flies at a high altitude.
Our sales manager flies to Singapore twice a year.
In each sentence, the subject is singular and the verb is therefore flies.
A quick grammar test
Replace the subject with they.
The bird flies south.
They fly south.
If they fly sounds right, the original singular form is probably flies:
The bird flies south.
Key takeaway: Use flies after he, she, or it when fly is the present-tense verb.
“Flies” as a Noun
Flies is also the plural form of the noun fly.
Singular:
There is a fly on the wall.
Plural:
There are flies on the wall.
Cambridge and Oxford both identify flies as the plural of the noun fly.
More examples
Daily conversation
I need to get rid of these flies.
Education
The student observed how flies behaved around the food.
News or informational writing
Flies can be found in many different environments.
Workplace
Please keep the kitchen door closed to prevent flies from entering.
How to tell whether “flies” is a noun
Look at what the word is doing in the sentence.
Flies are everywhere.
Here, flies is the subject and names insects. It is a noun.
Compare:
The bird flies every morning.
Here, flies describes an action. It is a verb.
The spelling is identical, but the grammatical function is different.
Key takeaway: The same word flies can be either a plural noun or a third-person singular verb.
Fly, Flies, Flew, Flown, or Flying?
This is where learners often get confused. These words belong to the same verb family, but they do different jobs.
| Form | Function | Example |
| fly | base/present form | Birds fly south. |
| flies | third-person singular present | The eagle flies high. |
| flew | simple past | The bird flew away. |
| flown | past participle | The bird has flown away. |
| flying | -ing form | The bird is flying. |
Cambridge gives the main verb forms as fly – flew – flown, while Oxford also identifies flies and flying in the verb paradigm.
The most important distinction
Do not use flies when you mean past tense.
Incorrect:
Yesterday, the bird flies away.
Correct:
Yesterday, the bird flew away.
Likewise, after has, have, or had, use flown, not flies:
The bird has flown away.
Why this matters
Fly is an irregular verb. Its past form is not flyed. Instead, it changes to flew, with flown as the past participle.
Key takeaway: Present singular = flies; simple past = flew; past participle = flown.
Flys vs. Flies: Side-by-Side Comparison
| Word | Standard English? | Typical meaning | Example |
| fly | Yes | base verb/singular noun | I fly often. |
| flies | Yes | plural noun or singular verb | The plane flies daily. |
| flys | Usually no | Common spelling error | ❌ The bird flys away. |
| flew | Yes | past tense | The bird flew away. |
| flown | Yes | past participle | The bird has flown away. |
| flying | Yes | -ing form | The bird is flying. |
Is “flys” ever correct?
In ordinary modern English, flys should not be used as the standard spelling of the plural noun fly or the third-person singular verb fly.
There can be specialized names, trademarks, usernames, product names, or other proper names that deliberately use unusual spellings. Those are exceptions based on naming rather than ordinary English grammar.
For normal writing, choose flies.
Key takeaway: If you are writing a normal English sentence and are choosing between flys and flies, choose flies.
Common Mistakes With “Flys” and “Flies”
Mistake 1: Adding only “s”
Wrong:
The bird flys across the sky.
Correct:
The bird flies across the sky.
Why it happens: Writers remember that third-person singular verbs usually take -s, but forget that words ending in consonant + y change spelling.
How to avoid it: Apply the y → ies rule.
Mistake 2: Using “flies” for the past
Wrong:
The plane flies to New York yesterday.
Correct:
The plane flew to New York yesterday.
Why it happens: Flies looks like a completed action to some learners, but it is a present-tense form.
How to avoid it: Look for a past-time marker such as yesterday, last week, or earlier. If the action is finished in the past, use flew.
Mistake 3: Writing “flyes”
Wrong:
There are many flyes in the room.
Correct:
There are many flies in the room.
The standard plural changes y to i and adds -es.
Mistake 4: Using “fly” after a singular subject
Wrong:
My sister fly to Lahore every month.
Correct:
My sister flies to Lahore every month.
But:
My sisters fly to Lahore every month.
The difference is subject-verb agreement.
Key takeaway: Check both the spelling rule and the subject before choosing fly or flies.
A Simple Decision Guide
When you’re stuck, use this sequence:
Are you talking about more than one insect?
→ Yes → flies
I saw three flies.
Are you describing what one person, animal, aircraft, or thing does now or regularly?
→ Yes → flies
The eagle flies over the valley.
Are you talking about I, you, we, or they?
→ Use fly
They fly every summer.
Are you describing a completed action in the past?
→ Use flew
They flew home yesterday.
Are you using has, have, or had before the verb?
→ Use flown
They have flown home.
This decision tree solves most everyday questions about these forms.
Special Meanings of “Flies”
The word flies is not limited to insects and ordinary verb forms.
In British English, flies can refer to the opening at the front of trousers. Cambridge notes this usage, and Oxford also lists it.
For example:
His flies were undone.
There is also a theatrical meaning in the expression “the flies.” Oxford defines this as the space above a theater stage used for lighting and storing scenery.
These meanings are much less likely to cause the flys vs. flies spelling question, but they show why context matters.
Related expressions
English also contains expressions such as:
- time flies — time passes quickly
- a fly on the wall — someone who watches without being noticed
- a fly in the ointment — something that causes a problem
- on the fly — done quickly or while something else is happening
Oxford lists these idiomatic uses under fly.
Key takeaway: Context can give flies meanings beyond the ordinary plural noun and verb form.
Expert Editing Tip: Look at the Word Before “Fly”
A fast proofreading method is to examine the subject and the time expression.
Compare:
The bird flies every morning.
The birds fly every morning.
The bird flew yesterday.
The bird has flown away.
The change is not random. It reflects three different grammar questions:
- Who is the subject?
- When did the action happen?
- Which verb form does the sentence require?
This is more reliable than trying to memorize flys versus flies as an isolated spelling question.
For students, editors, and professional writers, learning the pattern is more useful than memorizing one word.
Mini Quiz: Fly or Flies?
Choose the correct form.
- The airplane ___ over the city every evening.
- Several ___ are sitting near the window.
- We ___ to Karachi next week.
- She ___ to London twice a year.
- The bird ___ away yesterday.
- The bird has ___ away.
- My friends ___ home every summer.
- A ___ landed on my notebook.
Answers
- flies
- flies
- fly
- flies
- flew
- flown
- fly
- fly
The useful lesson is that the correct answer depends on grammar and meaning, not simply on how the word sounds.
Frequently Asked Questions
Is “flys” a real English word?
Flys is not the standard spelling for the common plural of fly or the third-person singular form of the verb fly. In ordinary English, use flies.
Is “flies” singular or plural?
It can be either. Flies is plural when it means more than one insect. It is singular in grammatical agreement when it is the verb form used with he, she, or it.
What is the plural of fly?
The standard plural is flies.
One fly → two flies.
Oxford and Cambridge both list flies as the plural form.
What is the past tense of fly?
The usual past tense is flew.
The plane flew over the mountains.
Cambridge and Oxford both identify flew as the past tense of fly.
What is the past participle of fly?
The past participle is flown.
The plane has flown to Dubai.
Oxford lists flown as the past participle.
Why does fly become flies?
Because fly ends in a consonant followed by y. In standard inflection, the y changes to i before -es is added.
fly → flies
The same pattern appears in words such as try → tries and study → studies.
Is “flies” pronounced like “flys”?
Yes. In ordinary use, flies is pronounced /flaɪz/, essentially the same sound that a hypothetical spelling flys would suggest. The spelling difference is grammatical, not a difference in pronunciation. Cambridge gives the pronunciation of flies as /flaɪz/.
Is “flies” always related to the insect?
No. It can be the verb form of fly, as in “She flies to Paris,” or it can have other noun meanings, including the theatrical term “the flies.”
Is “fly” an irregular verb?
Yes. Its principal forms are fly – flew – flown, rather than a regular -ed past-tense pattern. Oxford lists these forms explicitly.
Should I use “flys” in formal writing?
No, unless Flys is intentionally part of a proper name, brand, title, username, or other official spelling. For normal formal English, use flies.
What is an easy way to remember “flies”?
Think:
One fly → many flies.
Then apply the same spelling pattern to the verb:
It flies.
If you remember those two examples, the correct spelling becomes much easier to recall.
Key Takeaways
- Flies is the standard spelling; flys is normally incorrect.
- Flies can be the plural noun: three flies.
- Flies can also be the third-person singular present verb: the bird flies.
- Fly is used with I, you, we, and they: they fly.
- The past tense is flew.
- The past participle is flown.
- The consonant + y → ies pattern explains fly → flies.
- Unusual spellings may occur in proper names, but they do not change the normal grammar rule.
Editorial Note
For standard English editing, the safest rule is simple: write “flies,” not “flys,” unless you are reproducing an intentional proper name or brand spelling. Dictionary evidence from Oxford and Cambridge supports flies as the standard plural noun and third-person singular verb form.
References
- Cambridge Dictionary — Fly
- Cambridge Dictionary — Flies
- Oxford Advanced Learner’s Dictionary — Fly (verb)
- Oxford Advanced Learner’s Dictionary — Fly (noun)
- Oxford Advanced Learner’s Dictionary — Flies
Conclusion
If you’re choosing between flys and flies, choose flies in standard English. The same spelling works in two common situations: “The bird flies” and “I saw several flies.” When you need the past tense, switch to flew, and after has, have, or had, use flown.
The simplest rule to remember is:
fly → flies, not flys.
When in doubt, check the subject and the time of the action. That quick habit will usually tell you which form belongs in the sentence.
David James is an English language enthusiast, writer, and author at StudyNixx, a website dedicated to helping readers understand confusing English words, spelling differences, and commonly mistaken word forms. He focuses on making English language learning simple, practical, and easy to understand.
David is also the author of two books on English language and word usage, where he explores common spelling mistakes, confusing words, and practical ways to improve written English. Through his writing and educational content, he helps students, writers, and everyday English learners choose the right words with confidence.
At StudyNixx, David covers common word comparisons such as summary vs. summery, shiny vs. shiney, spicy vs. spicey, and breached vs. breeched. His goal is to provide clear, useful, and reliable explanations that make English spelling and word usage easier for everyone.