Cool MateImpossible vs That'll be the day
When to use each in English, with meaning, register, and examples.
Impossible
Top 1,000 (very common)A2
That'll be the day
InformalBeyond 10,000 (less common)
Most formal: ImpossibleMost common: Impossible
| Impossible | That'll be the day | |
|---|---|---|
| Pronunciation | 🇬🇧 /["/ɪmˈpɒsəbl/"]/🇺🇸 /["/ɪmˈpɑːsəbl/"]/ | 🇬🇧 //ðætəl bi ðə deɪ//🇺🇸 //ðætəl bi ðə deɪ// |
| Meaning | Not able to happen or be done. | A phrase used to express doubt that something will happen. |
| Example | Climbing that mountain seems impossible without proper training. | He thinks he will win the lottery? That'll be the day. |
| Register | Neutral | Informal |
| How common | Top 1,000 (very common) | Beyond 10,000 (less common) |
| CEFR level | A2 | - |
| Collocations | appear, be, look, absolutely, completely, downright, for, be, become, find somebody, really, absolutely, completely | say that'll be the day, believe that'll be the day, think that'll be the day |
| 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'. | Misusing it as a literal prediction instead of expressing skepticism., Using it in serious or formal discussions where it may seem dismissive. |
| 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 in conversational contexts, often when discussing something unlikely to happen. Avoid in formal writing. |
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Frequently asked questions: Impossible vs That'll be the day
What's the difference between Impossible and That'll be the day?
Impossible: Not able to happen or be done. That'll be the day: A phrase used to express doubt that something will happen.
Which is more formal: Impossible and That'll be the day?
Impossible is the most formal of these.
Which is more common: Impossible and That'll be the day?
Impossible is the most common in everyday English.
Can you show an example of each?
Impossible: Climbing that mountain seems impossible without proper training. That'll be the day: He thinks he will win the lottery? That'll be the day.
Can I use Impossible and That'll be the day interchangeably?
Not always. Impossible and That'll be the day 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.