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when pigs fly

B1 idiom #13,456 most common 11 min read

when pigs fly

Practice it Examples Notes & Tips when pigs fly in 30 Seconds

Explanation when pigs fly in your Level:

At the A1 level, you are just starting to learn English. 'When pigs fly' is a funny phrase. It means 'no' or 'never'. Think about a pig. Can a pig fly? No, it cannot. So, if someone asks 'Can I have your car?' and you say 'When pigs fly!', it means 'No, you can never have my car'. It is a way to say that something is impossible. You use it with friends. Do not use it with your teacher or your boss. It is a joke. Just remember: Pigs don't fly, so the answer is 'No'. You can use it as a short answer. If a friend says, 'I will be the President one day,' you can laugh and say, 'When pigs fly!' This tells your friend that you think it is impossible. It is a very common idiom in English movies and cartoons. It is good to know so you don't think people are talking about real flying animals. English speakers like to use animals in their idioms. This one is very popular because it is easy to imagine. Imagine a big pink pig with wings. It looks silly, right? That is why the phrase is used for silly or impossible ideas. Keep it simple: 'When pigs fly' = 'Never'.

At the A2 level, you can start using more interesting expressions. 'When pigs fly' is an idiom used to express strong disbelief. If you think something will never happen, you use this phrase. It's more colorful than just saying 'never'. For example, if your brother says he will clean the whole house in ten minutes, you can say, 'Yeah, and pigs will fly!' This shows you are being sarcastic. Sarcasm is when you say the opposite of what you mean to be funny or to show you don't believe something. Grammatically, it's easy to use. You can say it by itself as a response. Or you can put it at the end of a sentence: 'I will go on a date with him when pigs fly.' This means you will never go on a date with him. It's important to remember that this is for informal situations. You should use it with people you know well. If you use it in a serious situation, people might think you are being rude. It's a great way to sound more like a native speaker because native speakers love using idioms to show their feelings. When you hear it, don't look at the sky for pigs! Just know that the person is saying 'No way!'

At the B1 level, you should understand that 'when pigs fly' is a classic example of an 'adynaton'. This is a fancy word for a figure of speech that uses an impossibility to describe an impossibility. It is used to express extreme skepticism. It is a very common part of colloquial English. You will hear it in movies, read it in novels, and hear it in daily conversation. The phrase is often used as a sarcastic retort. For instance, if someone makes a claim that is clearly false or highly unlikely, you can use this idiom to dismiss it immediately. It's also helpful to know the British variation: 'pigs might fly'. They mean the same thing. In terms of usage, it's often preceded by 'and' or 'yeah'. Example: 'He says he's going to stop smoking.' — 'Yeah, and pigs might fly.' This shows you don't believe him at all. You can also use it to set a condition that will never be met: 'I'll lend you money again when pigs fly.' This is a firm way of saying 'I will never lend you money again.' Because it's an idiom, the words don't change. You don't usually say 'when a pig flies' or 'when pigs flew'. Keeping the phrase exactly as it is helps people understand you better. It's a fun, slightly cheeky way to express doubt without being too aggressive.

At the B2 level, you can appreciate the rhetorical power of 'when pigs fly'. It's not just a way to say 'never'; it's a way to mock a suggestion or a prediction. It carries a tone of derision or playful mockery. You should be able to use it in various sentence structures. For example, you can use it in a 'when' clause: 'The day I agree to that will be the day when pigs fly.' This is more emphatic than a simple 'never'. You should also be aware of its synonyms and how they differ in intensity. 'When pigs fly' is generally humorous and informal. In contrast, 'when hell freezes over' is much more forceful and can be seen as slightly vulgar. 'Once in a blue moon' is often confused with 'when pigs fly', but as a B2 student, you should know the distinction: 'once in a blue moon' means very rarely, while 'when pigs fly' means not at all. You might also encounter it in a more sophisticated structure: 'Only when pigs fly will I consider that proposal.' This use of inversion for emphasis is a hallmark of more advanced English. Understanding the cultural context is also key; the pig is used because it is the antithesis of a flying creature—heavy, muddy, and earthbound. This contrast is what makes the idiom so effective and enduring in the English language.

At the C1 level, you should be exploring the nuances of register and the historical context of idioms like 'when pigs fly'. This expression is a prime example of how English speakers use hyperbole to manage social interactions. By using a humorous image to express disbelief, the speaker can mitigate the potential harshness of a direct refusal or a blunt 'you're lying'. It's a social lubricant for skepticism. You should also be aware of the phrase's etymology; it has been in use since at least the early 17th century, appearing in works like 'Withals' Dictionary' (1616) as 'pigs fly in the air with their tails forward'. Over time, it was shortened to the version we know today. As a C1 learner, you should be able to identify when the idiom is being subverted for comedic or literary effect. For example, if a character in a story actually sees a flying pig, it's a signal that the 'impossible' is happening, which is a common trope in magical realism. You should also be comfortable using it in more complex, nuanced conversations where the level of sarcasm needs to be finely tuned. For instance, using it with a slightly rising intonation can make it sound more like a playful tease, whereas a flat, falling intonation makes it sound like a cold dismissal. Mastering these prosodic features alongside the idiom itself is what characterizes a high-level speaker.

At the C2 level, 'when pigs fly' is more than just a vocabulary item; it's a tool for sophisticated rhetorical play. You should be able to analyze its function within the broader category of 'adynaton' and compare it with similar constructs in other languages or historical periods. In classical literature, such impossibilities were often used to emphasize the permanence of a vow or the depth of a feeling. In modern English, 'when pigs fly' has become a cultural touchstone, often referenced in advertising, political satire, and high-level journalism to succinctly dismiss absurdities. You should be able to use it with perfect timing in spontaneous conversation, perhaps even layering it with other idiomatic expressions for a more colorful effect. Furthermore, a C2 speaker should understand the subtle differences between 'when pigs fly', 'pigs might fly', and 'and pigs can fly'. While they all denote impossibility, the choice of modal verb can slightly shift the tone from a statement of fact to a more skeptical 'maybe' (though still meaning 'no'). You should also be aware of how the idiom interacts with modern technology and culture—for instance, the use of flying pig imagery in social media to signal that a news story is 'fake' or 'too good to be true'. At this level, your goal is to use the idiom not just correctly, but with a sense of its full historical and cultural weight, demonstrating a deep integration into the English-speaking world's shared conceptual metaphors.

Practice it Examples Notes & Tips

when pigs fly in 30 Seconds

An idiom meaning 'never' or 'impossible'.
Used sarcastically to show total disbelief.
The British version is 'pigs might fly'.
Informal register; best for friends and family.

The English language is rich with colorful expressions that convey skepticism, and few are as vivid or as widely recognized as the idiom 'when pigs fly'. At its core, this phrase is used to describe an event that is considered absolutely impossible. It functions as a sarcastic or humorous way of saying 'never'. When someone uses this expression, they are not just saying that an event is unlikely; they are asserting that the laws of nature would have to be fundamentally altered for the event to occur. The image of a heavy, ground-dwelling animal like a pig suddenly sprouting wings and taking to the skies is inherently ridiculous, which is precisely why it serves as such an effective metaphor for impossibility. This type of figure of speech is known in linguistics as an adynaton—a form of hyperbole so extreme that it involves a complete physical impossibility.

Core Meaning: The phrase indicates that a specific event will never happen because it is as impossible as a pig flying through the air.

Historically, humans have always used the natural world to illustrate their doubts. In ancient times, people might have said 'when the Nile flows backward' or 'when the sun rises in the west'. The English version involving pigs has been around for centuries, appearing in various forms since the 1600s. It is most commonly used in informal conversations, often as a quick retort to a claim that seems far-fetched. For instance, if a notoriously lazy friend says they are going to run a marathon tomorrow, you might respond with, 'Sure, and pigs will fly!'

'I think the boss is going to give us all a fifty percent raise this year.' — 'Yeah, when pigs fly!'

The phrase is also versatile in its phrasing. You might hear 'pigs might fly' (common in British English) or 'and pigs will fly' or simply the adverbial phrase 'when pigs fly'.

Cultural Nuance: In many cultures, the pig is seen as the ultimate symbol of being grounded and ungraceful, making the contrast with flight even more striking.

'Do you think they will ever stop arguing?' — 'When pigs fly, maybe.'

Synonymous Imagery: It shares a semantic space with 'hell freezes over' or 'a cold day in hell', though 'when pigs fly' is generally seen as less aggressive and more whimsical.

'He says he'll pay you back when pigs fly.'

'I'll clean my room when pigs fly!' shouted the teenager.

'The two rival teams will merge when pigs fly.'

Understanding this idiom is crucial for anyone looking to grasp the nuances of English sarcasm. It is not just about the literal impossibility, but the attitude of the speaker—one of playful yet firm disbelief. It allows for a creative way to say 'no' without being overly blunt, using a shared cultural image to lighten the mood of a disagreement. Whether you're watching a sitcom or chatting with colleagues, you're likely to encounter this airborne porcine metaphor frequently.

Using 'when pigs fly' correctly requires an understanding of its grammatical role and the social context of the conversation. Most commonly, it acts as a response to a statement or as an adverbial clause indicating time (or rather, the lack thereof). Because it is an idiom of impossibility, it is almost always used in the future tense or in conditional structures.

Sentence Structure: It can be used as a standalone exclamation: 'When pigs fly!' or as part of a longer sentence: 'I will do that when pigs fly.'

One of the most effective ways to use this phrase is to highlight the absurdity of a prediction. If someone suggests that a notoriously corrupt politician will suddenly become honest, a listener might say, 'He'll be honest when pigs fly.' Note how the idiom takes the place of a time expression like 'tomorrow' or 'next week'.

'Will you ever go skydiving with me?' — 'Sure, when pigs fly!'

In British English, a common variation is 'pigs might fly'. This is often used as a sarcastic retort to someone else's optimistic statement. If person A says, 'I might win the lottery this weekend,' person B might respond, 'And pigs might fly.' This implies that the chance of winning the lottery is as likely as pigs taking flight.

Tone and Sarcasm: The tone is usually lighthearted but can be biting depending on the relationship between the speakers.

'I'll finish this report by midnight.' — 'Yeah, and pigs might fly.'

Placement in Narrative: In writing, it is almost exclusively found in dialogue. It adds a natural, colloquial feel to characters' speech.

The old man scoffed, 'They'll build a bridge over this canyon when pigs fly.'

'She'll apologize to him when pigs fly.'

'I'll believe that when pigs fly,' he muttered under his breath.

It is also possible to use it in a more complex sentence to show a conditional impossibility. 'Only when pigs fly will I ever agree to work for that company again.' This inversion (Starting with 'Only when...') adds a dramatic, emphatic flair to the statement, making the refusal sound very final. By mastering these different structures, you can use the idiom to add color and personality to your spoken English, ensuring your skepticism is heard loud and clear.

You will encounter 'when pigs fly' in a variety of settings, ranging from casual family dinners to pop culture references. Its primary home is in informal spoken English. It is a favorite of parents responding to unlikely requests from children, friends teasing each other about unrealistic goals, and coworkers venting about improbable corporate promises.

In Media: The phrase is a staple in television sitcoms and movies, often used for comedic effect when a character makes a ridiculous prediction.

For example, in the animated show 'The Simpsons', there is a famous scene where a pig is actually seen flying past a window, prompting a character to realize that an impossible event is actually happening. This play on words relies on the audience's deep familiarity with the idiom.

'I'll give you a million dollars.' — 'Sure, when pigs fly!'

In literature, the idiom is often used to establish a character's cynical nature. A character who frequently says 'when pigs fly' is likely someone who is grounded in reality and doesn't have much patience for nonsense or idealistic dreams.

In Politics: Political commentators often use it to describe the likelihood of rival parties reaching a consensus on a controversial issue.

'The two countries will sign a peace treaty when pigs fly,' the journalist remarked.

In Sports: Fans of underdog teams might use the phrase when talking about their team's chances of winning a championship against a powerhouse opponent.

'We'll beat the champions when pigs fly.'

'I'll start waking up at 5 AM when pigs fly.'

'They'll lower the taxes when pigs fly.'

Because it is so recognizable, you will also see it used in advertising. A company might use the slogan 'Until pigs fly, we'll keep doing X' to emphasize their commitment to a traditional or reliable service. In all these contexts, the idiom serves as a shorthand for 'it's not going to happen', saving the speaker from having to give a long explanation of why they are skeptical. It's a linguistic tool that combines cultural history with immediate, relatable imagery.

Despite its popularity, there are several common mistakes that learners of English—and even native speakers—make when using 'when pigs fly'. The most frequent error is taking the phrase too literally. Because idioms are figurative, their meaning cannot be deduced from the individual words. A learner might mistakenly think the phrase refers to a specific time or a biological anomaly, rather than a general state of impossibility.

Literal Interpretation: Mistaking the phrase for a real condition. For example, asking 'What kind of pigs?' or 'How high do they fly?' misses the point entirely.

Another mistake is using the phrase in the wrong register. It is a highly informal idiom. Using it in a formal academic paper, a legal document, or a serious business presentation can make the speaker or writer appear unprofessional or disrespectful. For example, saying 'The company will reach its targets when pigs fly' in a board meeting would likely be seen as a grave insult to the management's efforts.

Incorrect: 'The scientific results will be validated when pigs fly.' (Too informal for science).

Confusion between the American 'when pigs fly' and the British 'pigs might fly' is common, though they are interchangeable in meaning. However, mixing them into 'when pigs might fly' is non-standard and sounds awkward.

Grammatical Errors: Using the past tense incorrectly. You shouldn't say 'It happened when pigs flew' because the whole point is that it never happens.

Incorrect: 'I will pay you when a pig flies.' (Usually plural 'pigs' is used).

Overuse: Using the phrase too often can make your speech sound repetitive or overly cynical. It's best reserved for moments of genuine, humorous disbelief.

Incorrect: 'I'll go to the store when pigs fly.' (If you actually intend to go, this is confusing).

Incorrect: 'When pigs fly, it will be Tuesday.' (This mixes a real time with an impossible one, which is nonsensical).

Incorrect: 'He said pigs fly when he is happy.' (The order is almost always 'when pigs fly').

Finally, some people confuse it with other animal-related idioms like 'the elephant in the room' or 'dog days', which have completely different meanings. Remembering that 'when pigs fly' is strictly about impossibility will help you avoid these pitfalls and use the phrase with confidence.

If you find yourself using 'when pigs fly' too often, or if you need a phrase that fits a slightly different context, there are many alternatives in English. Each has its own nuance, level of formality, and intensity.

Hell Freezes Over: This is a much stronger and more emphatic version. It implies a definitive, often angry, refusal. 'I'll work for him again when hell freezes over!'

This alternative is common but can be considered mild profanity in some conservative circles, so 'when pigs fly' is the safer, more 'family-friendly' choice. Another common alternative is 'not in a million years'. This is very common and lacks the humorous imagery of the pig idiom, making it slightly more direct and serious.

'Will you move to the city?' — 'Not in a million years.'

Don't Hold Your Breath: This is used when someone is waiting for something that is unlikely to happen. It suggests that if they wait for it, they will run out of air before it occurs.

'He said he'd call me back today.' — 'Don't hold your breath.'

In more formal or academic contexts, you should avoid idioms altogether and use words like 'impossible', 'unattainable', or 'implausible'. These words convey the same meaning without the informal baggage.

Fat Chance: This is a very short, sarcastic way of saying there is no chance at all. Interestingly, 'slim chance' means the same thing, even though 'fat' and 'slim' are opposites.

'Maybe they'll let us leave early.' — 'Fat chance!'

'I'll believe that when hens grow teeth.' (An older, less common variation).

'That will happen when the sun rises in the west.'

By knowing these alternatives, you can tailor your level of skepticism to the situation, choosing between the humor of flying pigs, the intensity of frozen hell, or the directness of a million years. This variety makes your English sound more natural and sophisticated.

How Formal Is It?

Formal

Neutral

Informal

Child friendly

Slang

Fun Fact

Lewis Carroll used a variation in 'Alice's Adventures in Wonderland' when the Duchess says, 'and the moral of that is—"Birds of a feather flock together."' and Alice responds by thinking about pigs flying.

Pronunciation Guide

UK /wen pɪɡz flaɪ/

US /wɛn pɪɡz flaɪ/

The primary stress is on 'pigs' and 'fly'.

Rhymes With

When figs buy When wigs die When digs lie When bigs try When twigs dry When jigs sigh When rigs tie When pigs cry

Common Errors

Saying 'when pig fly' (forgetting the 's' on pigs).
Pronouncing 'pigs' with a long 'e' sound.
Confusing the vowel in 'when' with 'wan'.
Putting too much stress on 'when'.
Pronouncing 'fly' like 'flee'.

Difficulty Rating

Reading 2/5

Easy to recognize in text once the concept of idioms is understood.

Writing 3/5

Requires knowledge of informal register and correct plural usage.

Speaking 3/5

Requires correct tone and sarcasm to be effective.

Listening 2/5

Usually clear, but the British variation might confuse some.

What to Learn Next

Prerequisites

Pig Fly Never Impossible Sarcastic

Learn Next

Once in a blue moon Piece of cake Break a leg Under the weather Cost an arm and a leg

Advanced

Adynaton Hyperbole Rhetorical device Idiomaticity Colloquialism

Grammar to Know

Conditionals with 'when'

I will go when he arrives. (Real) / I will go when pigs fly. (Impossible condition)

Negative Inversion

Only when pigs fly will I agree. (The auxiliary 'will' comes before the subject)

Plural Nouns

Pigs (plural) is required for the idiom; 'when a pig flies' is non-standard.

Modal Verbs for Possibility

Pigs *might* fly (British) vs. Pigs *will* fly (American/Retort).

Future Tense in Time Clauses

Use present simple after 'when' even for future meaning: 'when pigs *fly*' (not 'will fly').

Examples by Level

Will you eat broccoli? When pigs fly!

Never!

Used as a short exclamation.

He will give me his toy when pigs fly.

He will never give it to me.

Used at the end of a sentence.

When pigs fly, I will clean my room.

I will not clean my room.

Used at the beginning of the sentence.

She says she can jump over the house. Yeah, when pigs fly!

That is impossible.

Sarcastic response.

I will be a cat when pigs fly.

I will never be a cat.

Simple future tense structure.

Will it rain candy? When pigs fly!

No, it won't.

Exclamatory response.

You will win the race when pigs fly.

You won't win.

Direct statement of impossibility.

Is he nice? Only when pigs fly.

He is never nice.

Using 'only' for emphasis.

I'll believe that story when pigs fly.

I don't believe the story at all.

Common collocation with 'believe'.

My sister will share her clothes when pigs fly.

She is very selfish with her clothes.

Subject + will + verb + when pigs fly.

Sure, and pigs might fly too!

I am being very sarcastic.

British variation with 'might'.

He'll arrive on time when pigs fly.

He is always late.

Focus on habitual behavior.

When pigs fly, I'll go swimming in the ocean.

I am afraid of the ocean.

Initial clause placement.

The dog will start talking when pigs fly.

Dogs can't talk.

Used for biological impossibilities.

Will you buy me a new phone? When pigs fly!

No, I won't buy it.

Response to a request.

I'll finish my homework early when pigs fly.

I always finish late.

Self-deprecating humor.

He thinks he'll be a millionaire by next year. Yeah, and pigs might fly.

That's a very unlikely dream.

Use of 'and' to join the retort.

I'll agree to go on a second date with him when pigs fly.

The first date was terrible.

Expressing a firm refusal.

The two politicians will agree on the budget when pigs fly.

They are always fighting.

Applying the idiom to a professional context.

I'll learn to play the violin in a week when pigs fly.

Learning an instrument takes a long time.

Highlighting an unrealistic timeframe.

He says he's given up sweets forever. When pigs fly!

He loves sugar too much to quit.

Short sarcastic interjection.

My car will start working again when pigs fly.

The car is completely broken.

Describing a broken object.

Only when pigs fly will I forgive him for what he did.

I am very angry and won't forgive him.

Advanced 'Only when' inversion.

I'll believe the weather report when pigs fly.

The weather reports are often wrong.

Expressing distrust in a source.

If you think I'm going to jump off that bridge, you'll have to wait until pigs fly.

I am never going bungee jumping.

Using 'until' instead of 'when'.

The manager said we'd get a bonus this month, but I'll believe it when pigs fly.

I don't trust the manager's promise.

Contrasting a statement with personal belief.

He claims he can run a mile in four minutes. Sure, and pigs might fly!

That's an Olympic-level speed he can't achieve.

Mocking a boastful claim.

When pigs fly, the city will finally fix the potholes on this street.

The roads have been bad for years.

Social/Civic commentary.

I'll wear that ridiculous costume when pigs fly and not a moment sooner.

I refuse to wear it.

Adding 'not a moment sooner' for emphasis.

They'll lower the price of gas when pigs fly.

Gas prices only seem to go up.

Expressing a cynical view on economy.

My computer will stop crashing when pigs fly.

The computer is extremely unreliable.

Personification of technology.

I'll be able to afford a mansion when pigs fly.

I don't have enough money.

Reflecting on financial status.

The idea that the two rival factions will reach a compromise is a 'when pigs fly' scenario.

It is a completely impossible situation.

Using the idiom as an adjective phrase.

He's been promising to renovate the kitchen for years, but I suspect it'll happen when pigs fly.

He is procrastinating indefinitely.

Using 'suspect' to add nuance to the doubt.

Only when pigs fly will that company prioritize environmental ethics over profit.

They are too focused on money.

Inversion for formal rhetorical effect.

To suggest that he will resign voluntarily is to believe that pigs will fly.

He will never quit on his own.

Infinitive structure 'To suggest... is to believe...'.

The likelihood of a peaceful resolution is about as high as the chance of pigs flying.

There is zero chance of peace.

Comparative structure.

I'll consider your offer when pigs fly, and even then, I might say no.

The offer is terrible.

Extending the idiom for extra sarcasm.

She'll admit she was wrong when pigs fly, given her legendary stubbornness.

She never admits her mistakes.

Adding a 'given' clause for context.

The tech giant will stop collecting user data when pigs fly.

Data collection is their business model.

Critique of corporate behavior.

The prospect of universal nuclear disarmament remains, for the foreseeable future, in the realm of 'when pigs fly'.

It is a utopian, impossible dream.

Using the idiom within a complex prepositional phrase.

Given the current geopolitical climate, a unified global currency will happen only when pigs fly.

Nations are too divided for this.

Integrating the idiom into a sophisticated political analysis.

To posit that human nature will fundamentally change is to wait for the day when pigs fly.

Human nature is constant and unlikely to change.

Using 'posit' and 'fundamental' for academic register.

He’ll stop seeking validation from others when pigs fly; it’s too deeply ingrained in his psyche.

His need for approval is permanent.

Using the idiom to describe a psychological trait.

The notion that we can achieve absolute zero waste in a consumerist society is a 'when pigs fly' proposition.

It's an unrealistic goal given the current system.

Using 'notion' and 'proposition' for high-level discourse.

I’ll believe the sincerity of his apology when pigs fly, or perhaps slightly after.

I will never believe he is truly sorry.

Adding a humorous 'after' clause to subvert the idiom.

When pigs fly, the various departments will finally communicate effectively without bureaucratic interference.

The bureaucracy is a permanent obstacle.

Satirical look at organizational structure.

The artist claimed he would stop painting when pigs fly, suggesting it was his life's sole purpose.

He will paint until the day he dies.

Narrative use of the idiom to show commitment.

Synonyms

when hell freezes over never in a million years not in a month of Sundays at the Greek calends a cold day in hell

Antonyms

any day now inevitably bound to happen

Common Collocations

Believe it when pigs fly

Yeah, and pigs might fly

Only when pigs fly

Until pigs fly

Wait for pigs to fly

A 'when pigs fly' situation

Happen when pigs fly

Agree when pigs fly

Change when pigs fly

Pay back when pigs fly

Common Phrases

And pigs will fly

— A sarcastic addition to an unlikely statement.

He'll be on time, and pigs will fly.

Pigs might fly

— The British version of the idiom.

Pigs might fly before he admits he's wrong.

When pigs sprout wings

— A less common variation of the same idiom.

I'll go when pigs sprout wings.

I'll believe that when pigs fly

— A standard way to express skepticism.

You finished the book? I'll believe that when pigs fly.

When pigs fly and cows jump over the moon

— Combining two nursery rhyme/idiom images for extra effect.

That'll happen when pigs fly and cows jump over the moon.

Sure, and I'm the Queen of England

— Another way to show disbelief by claiming something impossible.

You're a genius? Sure, and I'm the Queen of England.

That'll be the day

— Expressing that an event is very unlikely to happen.

He's cleaning? That'll be the day!

In your dreams

— A blunt way to say something won't happen.

I'm going to win. — In your dreams!

Tell it to the marines

— An old idiom meaning 'I don't believe you'.

You saw a UFO? Tell it to the marines.

Pull the other one

— Short for 'pull the other leg', meaning 'you are joking'.

He's a millionaire? Pull the other one!

Often Confused With

when pigs fly vs Once in a blue moon

Means 'very rarely', not 'never'. This is the most common confusion.

when pigs fly vs Flying pigs

A literal description of pigs in the air, not the idiom.

when pigs fly vs When the sun rises

Something that happens every day (certainty), whereas pigs flying is impossible.

Idioms & Expressions

"Once in a blue moon"

— Something that happens very rarely.

We go to the theater once in a blue moon.

Informal

"A cold day in hell"

— Used to say that something will never happen.

It'll be a cold day in hell before I talk to him again.

Informal/Strong

"When the cows come home"

— For a very long time, or never.

You can talk until the cows come home, but he won't listen.

Informal

"To cry wolf"

— To give a false alarm.

If you cry wolf too often, no one will believe you.

Neutral

"The elephant in the room"

— An obvious problem that no one wants to discuss.

His drinking was the elephant in the room.

Neutral

"Fish out of water"

— Someone who is uncomfortable in a specific situation.

He felt like a fish out of water at the formal party.

Informal

"Wild goose chase"

— A hopeless or pointless search.

They sent me on a wild goose chase for a non-existent file.

Neutral

"Let the cat out of the bag"

— To reveal a secret.

Who let the cat out of the bag about the surprise party?

Informal

"Straight from the horse's mouth"

— From the highest or most reliable authority.

I heard the news straight from the horse's mouth.

Informal

"Kill two birds with one stone"

— To achieve two things with one action.

I'll drop you off on my way to work and kill two birds with one stone.

Neutral

Easily Confused

when pigs fly vs Pig

Literal animal vs. idiomatic use.

In the idiom, the pig is a symbol of impossibility, not a real animal.

I saw a pig on the farm. vs. He'll win when pigs fly.

when pigs fly vs Fly

Multiple meanings (insect vs. verb).

In this idiom, it is always the verb meaning to move through the air.

A fly is on the wall. vs. Pigs will fly.

when pigs fly vs Might

Used in the British version.

In the idiom, 'might' doesn't mean 'maybe'; it still means 'never'.

It might rain. vs. Pigs might fly.

when pigs fly vs When

Usually indicates a real time.

Here, it indicates a time that will never exist.

When is the party? vs. When pigs fly.

when pigs fly vs Never

Direct synonym.

'Never' is neutral; 'when pigs fly' is colorful and sarcastic.

I never go there. vs. I'll go there when pigs fly.

Sentence Patterns

When pigs fly!

I'll [verb] when pigs fly.

I'll do it when pigs fly.

Yeah, and pigs might fly.

It'll happen when pigs fly.

Only when pigs fly will I [verb].

Only when pigs fly will I go.

That is a 'when pigs fly' scenario.

He says [claim], but when pigs fly!

He says he's rich, but when pigs fly!

Will [subject] [verb]? When pigs fly!

Will he help? When pigs fly!

Word Family

How to Use It

frequency

High in spoken English, Low in academic writing.

Common Mistakes

When pig fly → When pigs fly
The noun 'pigs' must be plural in this fixed idiomatic expression.
When pigs will fly → When pigs fly
In time clauses starting with 'when', we use the present simple tense, not the future 'will'.
Using it in a formal report → It is unlikely to occur
'When pigs fly' is too informal and sarcastic for professional or academic writing.
Confusing it with 'once in a blue moon' → Use 'when pigs fly' for 'never'
'Once in a blue moon' means something happens rarely, but it *does* happen. 'When pigs fly' means never.
Saying 'when pigs flew' → When pigs fly
The idiom is almost always used in the present/future context. It doesn't have a past tense form.

Tips

Master the Sarcasm

The key to this idiom is the 'Yeah, right' attitude. Practice saying it with a skeptical tone of voice to sound more like a native speaker.

Keep it Plural

Always use 'pigs' (plural). Saying 'when a pig flies' is a common mistake for learners and sounds slightly off to native ears.

Know Your Audience

Save this for friends, family, and close colleagues. In a job interview or a formal letter, it's better to use more direct language.

British Variation

If you are in the UK, listen for 'pigs might fly'. It's the same meaning, just a slightly different choice of words.

Dialogue Only

Try to use this idiom mostly in dialogue. It adds character to your writing and makes the speech sound authentic.

Visual Learning

Draw a pig with wings on a sticky note and write 'NEVER' next to it. Put it on your desk to help you remember the idiom's meaning.

The 'Yeah' Prefix

Start your response with 'Yeah' or 'Sure' to set the sarcastic tone: 'Sure, when pigs fly!'

Cartoon Context

Watch old cartoons. They often use this idiom literally for a joke, which helps you see how famous and common it is.

Synonym Check

Don't confuse it with 'once in a blue moon'. One means 'rarely', the other means 'never'. This is a very important distinction.

Pop Culture

Look for the flying pig on the Pink Floyd 'Animals' album cover. It's a great example of how this idiom has entered modern art.

Memorize It

Mnemonic

Think of a Pig with Propellers. Since a pig is too heavy to fly, the event you're talking about is too 'heavy' (impossible) to happen.

Visual Association

Imagine a pink pig wearing a pilot's helmet and goggles, trying to take off but failing miserably.

Word Web

Impossible Never Sarcasm Pigs Wings Sky Joke Doubt

Challenge

Try to use 'when pigs fly' in a conversation today when a friend makes an unlikely promise. See if they understand your sarcasm!

Word Origin

The phrase has been used in various forms since the early 17th century. It appears in a 1616 dictionary by John Withals.

Original meaning: The original version was 'pigs fly in the air with their tails forward', which emphasized the absurdity of the image.

Germanic (English origin).

Cultural Context

Generally safe, but can be perceived as rude if used to dismiss someone's genuine dreams or feelings.

Common in the US, UK, Canada, and Australia. The 'might' vs 'will' variation is the main regional difference.

The Simpsons (flying pig scene) Pink Floyd's 'Animals' album cover (flying pig over a power station) Alice in Wonderland

Practice in Real Life

Real-World Contexts

Responding to a lie

You're kidding, right?
When pigs fly!
I don't believe you.
Pull the other one.

Refusing a request

Not a chance.
When pigs fly.
In your dreams.
No way.

Discussing sports

They'll win when pigs fly.
Fat chance for them.
It's impossible.
Don't hold your breath.

Workplace banter

A raise? When pigs fly!
Yeah, and pigs might fly.
Sure thing...
In another life.

Talking about habits

He'll quit when pigs fly.
Never going to happen.
He's always like that.
Only in his dreams.

Conversation Starters

"Do you think people will live on Mars soon, or is that a 'when pigs fly' kind of idea?"

"What's something your parents told you would happen 'when pigs fly'?"

"Have you ever seen something happen that you thought would only happen when pigs fly?"

"Is there an idiom in your language that means the same thing as 'when pigs fly'?"

"If someone said they would give you a million dollars tomorrow, would you say 'when pigs fly'?"

Journal Prompts

Write about a time you achieved something that you previously thought would happen 'when pigs fly'.

Describe a situation where you had to use the phrase 'when pigs fly' to someone.

Compare 'when pigs fly' with a similar idiom from your native language. How are they different?

Do you think it's good to be cynical (using 'when pigs fly') or should people be more optimistic?

Imagine a world where pigs actually fly. How would this change the meaning of the idiom?

Frequently Asked Questions

10 questions

It can be. It's sarcastic, so if you use it to dismiss someone's serious dream, it might hurt their feelings. Use it with friends for best results.

In the UK, people often say 'pigs might fly' or 'and pigs might fly'. Both mean the same thing as the American version.

It's not standard. The idiom is almost always plural: 'when pigs fly'. Using the singular sounds unnatural to native speakers.

Pigs are traditionally seen as heavy, clumsy, and very 'grounded' animals. The contrast with the grace and lightness of flight makes the impossibility very clear.

Generally, no. It's too informal. Use 'unlikely' or 'not feasible' instead to remain professional.

No. 'Once in a blue moon' means something happens very rarely. 'When pigs fly' means it will never happen at all.

Not really. You wouldn't say 'It happened when pigs flew' because the idiom describes something that never happens.

Yes, 'when hens grow teeth' is an older one, but it's much less common today than the pig version.

Yes, it's often used as a sarcastic retort: 'Yeah, and pigs will fly!'

You could say 'That is a physical impossibility' or 'That event is highly improbable'.