Are there any rules for using can't and cannot since they mean the same thing, and they are used interchangeably, but they sound weird in certain contexts?


2 Answers 2


This answer at ELU suggests:

Grammatically, you can use can't instead of can not or cannot in the majority of circumstances. There is an exception. In wh-movement, the contraction should not be expanded unless you also change the word order:

Why can't I have some bacon? //OK
Why cannot I have some bacon? //not OK, archaic
Why can I not have some bacon? //OK again, although formal

Stylistically, the choice between can't and cannot is more complex. Generally, people use can't in speech and informal writing, and cannot or can not in formal writing or very formal speech. Also, cannot might be used when you need to carefully distinguish it from can't in speech.


I believe "cannot" is used in the more formal aspect, whereas "can't" is used in casual discussions and conversations.

  • I would just added that one should never use can't in a formal written form.
    – MasterPJ
    Commented Feb 1, 2013 at 9:03
  • 2
    In fact, we shouldn't be using contractions at all in formal writing.
    – Hydra
    Commented Feb 1, 2013 at 9:04
  • 3
    Never and not at all are a bit strong; conventional wisdom is relaxing this restriction. Grammar Girl says, "Use contractions in formal writing if it will sound stranger to avoid them than to use them". The Purdue OWL opined that contraction use is "sometimes dictated by what would otherwise appear as stilted language and over-formality". Even ELU evolved between 2010 and 2012.
    – J.R.
    Commented Feb 1, 2013 at 9:31

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