Cool MateImpossible vs When pigs fly
When to use each in English, with meaning, register, and examples.
Impossible
Top 1,000 (very common)A2
When pigs fly
InformalTop 5,000 (fairly common)
Most formal: ImpossibleMost common: Impossible
| Impossible | When pigs fly | |
|---|---|---|
| Pronunciation | 🇬🇧 /["/ɪmˈpɒsəbl/"]/🇺🇸 /["/ɪmˈpɑːsəbl/"]/ | 🇬🇧 //wɛn pɪɡz flaɪ//🇺🇸 //wɛn pɪɡz flaɪ// |
| Meaning | Not able to happen or be done. | Something that will never happen. |
| Example | Climbing that mountain seems impossible without proper training. | I'll believe she'll clean her room when pigs fly. |
| Register | Neutral | Informal |
| How common | Top 1,000 (very common) | Top 5,000 (fairly common) |
| CEFR level | A2 | - |
| Collocations | appear, be, look, absolutely, completely, downright, for, be, become, find somebody, really, absolutely, completely | believe it when pigs fly, expect it when pigs fly, do it when pigs fly, see it when pigs fly |
| Antonyms | possible, feasible, achievable | - |
| Common mistakes | 'Impossible' is sometimes confused with 'unbelievable' but they are not the same., Learners might use 'impossible' to describe very challenging tasks instead of things that cannot be done at all., 'Impossible' is often incorrectly combined with less strong modifiers, like 'very impossible'. | Used in serious contexts where a straightforward answer is needed., Misunderstood as a literal phrase rather than an idiom., Incorrectly interpreted as hopeful rather than negative. |
| Usage notes | Use 'impossible' to describe something that cannot be achieved. It’s suitable for both spoken and written English but may be too strong in polite contexts. | Used to express that something is impossible or very unlikely. More appropriate in casual conversation than in formal writing. |
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Frequently asked questions: Impossible vs When pigs fly
What's the difference between Impossible and When pigs fly?
Impossible: Not able to happen or be done. When pigs fly: Something that will never happen.
Which is more formal: Impossible and When pigs fly?
Impossible is the most formal of these.
Which is more common: Impossible and When pigs fly?
Impossible is the most common in everyday English.
Can you show an example of each?
Impossible: Climbing that mountain seems impossible without proper training. When pigs fly: I'll believe she'll clean her room when pigs fly.
Can I use Impossible and When pigs fly interchangeably?
Not always. Impossible and When pigs fly are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.