Cannot vs. Can Not
“Cannot” is the normal closed spelling for the negative of “can,” but “can not” is not universally wrong. Institutional and Chicago guidance document two-word uses when “not” is emphasized or belongs to a separate construction such as “not only” or a deliberate choice not to act.
Use “cannot” for ordinary “be unable to” negation. Use “can not” only when “not” has separate emphasis or scope; do not label every two-word occurrence as an error.
Key details
Choose the right form
| Meaning / situation | Construction | Decision |
|---|---|---|
| ordinary negative meaning “be unable to” | cannot | use the closed form in most cases |
| “not” has separate syntactic scope or emphasis | can not + separate construction | two words may be justified |
Quick tests
Negation-scope test
Does “not” simply negate “can” in the ordinary sense of inability?
If yes: Use “cannot.”
If no: If “not” belongs to another structure, such as “not only … but also,” keep the boundary required by that structure.
Caveat: Both forms are documented in context; avoid a simplistic rule that every two-word occurrence is wrong.
Examples
I cannot finish the report tonight.
Ordinary negative ability uses “cannot.”
She can not only edit but also design.
Here “not” belongs to the correlative “not only … but also” structure.
We cannot approve the request without the signed form.
This is ordinary negation, so the closed form is natural.
Usage notes
Use the closed form cannot in ordinary standard prose; two-word can not is reserved for narrower structural/emphatic cases.
Further guidance
Error Policy
The QA layer forbids treating a dictionary/style-documented contextual form as simply “incorrect.”
Scope Boundary
The Language Portal of Canada says both forms are correct but recommends “cannot” in most cases. Chicago likewise calls “can not” rarely necessary while documenting structural uses.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- cannot, can not (opens in a new tab)Language Portal of Canada · Both forms and structural conditions for two-word can not
- Chicago usage Q&A: cannot / can not (opens in a new tab)The Chicago Manual of Style · Ordinary negative cannot and rare structural can not