Can Not and Cannot

Cannot (one word) is the most common expansion of the contraction can't.

Can't can also be expanded to can not (i.e., two words), but this is less common and usually reserved for emphasis. For example: Of course, the words can and not sometimes appear alongside each other when the not forms part of another construction (such as not only). For example:

Cannot or Can Not?

Writers are often unsure whether to write cannot (one word) or can not (two words).

Cannot

Cannot (one word) is the usual expansion of the contraction can't. It is possible to write can not as two words, but this is usually reserved for emphasis. For example:

Can Not (When Not an Expansion of Can't)

Although rare, it is possible for can and not (just like any two words) to be situated alongside each other. This is most common with the correlative conjunction not only... but also. For example:
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See Also

Glossary of easily confused words What are correlative conjunctions? What are contractions? Glossary of common errors Glossary of grammatical terms