The English language is filled with small spelling distinctions that can create surprisingly persistent confusion. One of the most common examples is the question: “Flies or flys – which spelling is correct?” At first glance, both forms may look plausible. However, only one is correct in standard English usage. Understanding why will not only resolve this specific doubt but also strengthen your grasp of broader spelling patterns and grammatical rules.
TL;DR: The correct spelling is “flies”, not “flys.” “Flies” is the proper third-person singular form of the verb to fly and the plural of the noun fly. English spelling rules require changing the “y” to “ies” when a word ending in a consonant + y is pluralized or conjugated. “Flys” is almost always a misspelling.
The Short Answer: “Flies” Is Correct
In standard English, “flies” is the correct spelling in nearly all circumstances. The form “flys” is considered incorrect and does not appear in formal dictionaries except as a rare proper noun or surname.
“Flies” can serve two main grammatical purposes:
- The plural form of the noun fly (the insect).
- The third-person singular present tense of the verb to fly.
Examples:
- The room was filled with buzzing flies.
- She flies to New York every month for work.
In both examples, “flies” follows established spelling rules in English grammar.
Why “Flies” and Not “Flys”? Understanding the Rule
The difference comes down to a standard English spelling rule involving words that end in consonant + y.
When a noun or verb ends in a consonant followed by y, and you need to:
- Form the plural (for nouns), or
- Add “-s” for third-person singular present tense (for verbs),
You must replace the “y” with “ies.”
The Rule in Action
- Fly → Flies
- Baby → Babies
- City → Cities
- Cry → Cries
This rule exists to preserve pronunciation and maintain consistency within English spelling conventions.
Notice that the word fly ends in the consonant “l” followed by “y.” Because of this, when forming the plural or third-person singular form, the “y” changes to “ies.” Writing “flys” ignores this rule and is therefore incorrect in standard written English.
When Would “Flys” Ever Be Used?
In modern English, “flys” is almost never correct. However, there are limited and unusual contexts where it might appear:
- As a surname (e.g., someone named Mr. Flys).
- As a brand name or stylized trademark.
- As an archaic or obsolete spelling in very old texts.
Outside of these rare exceptions, “flys” is considered a spelling error.
One of the most common uses of “flies” is as the plural form of the insect fly.
Examples:
- The garbage attracted dozens of flies.
- Fruit flies gather around overripe bananas.
Just as you would not write “babys” for the plural of “baby,” you should not write “flys” for the plural of “fly.” The correct spelling follows the same pattern.
This spelling rule applies universally in modern English writing, whether formal or informal.
“Flies” as a Verb: Third-Person Singular of “To Fly”
The verb to fly follows the same consonant + y rule when conjugated in the present tense.
Consider the present tense forms:
- I fly
- You fly
- We fly
- They fly
- He/She/It flies
Only in the third-person singular do we add “-s.” But because “fly” ends in a consonant + y, the spelling changes to “flies” instead of “flys.”
Examples:
- The plane flies at 30,000 feet.
- He flies drones recreationally.
- Time flies when you are busy.
In every case, “flies” is grammatically correct. Writing “flys” would be a mistake.
What About Words That End in Vowel + Y?
To fully understand why “flies” is correct, it helps to examine the exception to the rule.
If a word ends in a vowel + y, you simply add “s” without changing the “y.”
Examples:
- Boy → Boys
- Key → Keys
- Play → Plays
- Enjoy → Enjoys
Notice that in “play,” the letter before “y” is “a” (a vowel). Therefore, “plays” keeps the “y.”
However, in “fly,” the letter before “y” is “l” (a consonant), so the spelling changes to “flies.”
This pattern consistently applies across standard English vocabulary.
Common Mistakes and Why They Happen
Why do people write “flys” if it is incorrect?
Several factors contribute:
- Phonetic confusion: The pronunciation of “flies” does not clearly signal the spelling change.
- Overgeneralization: Writers may incorrectly apply the simple “add s” rule used for most words.
- Typing errors: Fast digital communication often leads to shortcuts or misspellings.
Because English contains many irregularities, writers sometimes assume a simpler rule applies. However, “fly” is not irregular in this context—it follows a standard and predictable spelling pattern.
Historical Perspective on the Spelling
Historically, English spelling has evolved significantly. In Middle English, variations in spelling were common because there was no standardized dictionary. Over time, as printing became widespread and dictionaries formalized usage, consistent patterns—like changing consonant + y to “ies”—became standard practice.
By modern conventions, “flies” has long been established as the correct form. Major dictionaries such as Merriam-Webster, Oxford English Dictionary, and Cambridge Dictionary list “flies” as the plural and third-person singular form, with no recognition of “flys” as a standard variation.
Related Confusing Word Forms
The confusion between “flies” and “flys” mirrors similar spelling dilemmas:
- Carry → Carries (not carrys)
- Study → Studies (not studys)
- Reply → Replies (not replys)
Once you understand the consonant + y rule, you can confidently apply it to dozens of similar words.
How to Remember the Correct Spelling
If you struggle to remember whether to use “flies” or “flys,” keep this simple method in mind:
- Look at the letter before the “y.”
- If it is a consonant, remove the “y” and add “ies.”
- If it is a vowel, just add “s.”
For “fly”:
- The letter before “y” is “l.”
- “L” is a consonant.
- Therefore: “flies.”
This three-step process eliminates guesswork.
Final Verdict: Always Choose “Flies”
In virtually every writing situation, “flies” is the correct spelling. It serves as both the plural of the insect “fly” and the third-person singular form of the verb “to fly.” The spelling follows one of the most consistent rules in English: changing a consonant + y ending to “ies.”
The form “flys” does not meet standard grammatical requirements and should be avoided in formal, academic, and professional writing.
When in doubt, remember that English spelling conventions exist for clarity and pronunciation consistency. Applying the consonant + y rule correctly will ensure you never confuse “flies” and “flys” again.
In short, if you are writing about insects, airplanes, time passing quickly, or anything that takes to the air, the correct spelling is clear and well-established: flies.