I cannot do vs I can't

When to use each in English, with meaning, register, and examples.

I cannot do

Top 1,000 (very common)

I can't

High-frequency chunk
 I cannot doI can't
Pronunciation🇬🇧 //aɪ ˈkænɒt duː//🇺🇸 //aɪ ˈkænɑt du//🇬🇧 //aɪ kɑːnt//🇺🇸 //aɪ kænt//
MeaningI am unable to do something.I am unable to do something.
ExampleI cannot do my homework because I lost the instructions.I can't attend the meeting tomorrow.
RegisterNeutralNeutral
How commonTop 1,000 (very common)High-frequency chunk
Collocationsdo my homework, do this task, do any more work, do what is required, do the right thingI can't wait, I can't believe, I can't go
Common mistakesConfusing with 'I can't do' - 'cannot' is more formal., Omitting the action you cannot do - always specify what you cannot do.Confused with 'I can' leading to incorrect negation., Using in overly formal contexts., Omitting the subject by saying just 'can't'.
Usage notesUsed in various contexts to express inability. Suitable for both spoken and written English, but not overly formal.Use 'I can't' for informal refusal or inability. It's appropriate in casual conversation but less formal than 'I cannot'.

See it in real clips

I cannot do
I can't

Frequently asked questions: I cannot do vs I can't

What's the difference between I cannot do and I can't?

I cannot do: I am unable to do something. I can't: I am unable to do something.

Can you show an example of each?

I cannot do: I cannot do my homework because I lost the instructions. I can't: I can't attend the meeting tomorrow.

Can I use I cannot do and I can't interchangeably?

Not always. I cannot do and I can't 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.