cannot

cannot — modal verb

1. You use cannot instead of "can" to express a negative meaning: it tells you that

1.modal verbA1
Definition

You use cannot instead of "can" to express a negative meaning: it tells you that someone is not able to do something, does not have permission to do it, or that a situation makes it impossible. For example, saying "I cannot find my keys" means you have looked but failed; saying a restaurant cannot serve you means its rules or circumstances prevent it.

Example

Minh cannot find his keys anywhere in the house.

cannot + base verb (find)

I am sorry, but we cannot accept credit card payments here.

cannot + verb (permission / rules)

Common collocations
  • cannot possibly
  • simply cannot
  • just cannot
  • cannot afford to
  • cannot help + verb-ing
Synonyms
  • be unable to

    more formal; works in all tenses (e.g. 'was unable to', unlike cannot which is present only)

  • can't

    contracted form; very common in speech and informal writing

  • be not able to

    less common; used when a different tense is needed

Antonyms

Grammar Patterns

cannot + base verb

cannot possibly + base verb

cannot help + verb-ing

Usage Note

Spelling: The standard written form is the one-word 'cannot' (no space). The contraction 'can't' is common in speech and informal writing. The two-word form 'can not' is less common; it is used in formal writing for emphasis, especially before 'not only … but also …' or when the writer wants to stress the negative. ❌ 'I can not swim' (when you mean you are unable to swim). ✅ 'I cannot swim' or 'I can't swim.'

Common Mistakes

I cannot to swim.
I cannot swim.
After a modal verb like cannot, the main verb is always in the base form with no 'to.'
She cannot comes to the party.
She cannot come to the party.
The verb after cannot does not change for third person: no -s ending.
I can not open this jar.' (when meaning unable).
I cannot open this jar.' or 'I can't open this jar.
Use the one-word form for standard inability; two words are reserved for emphasis or formal constructions.

2. When you have strong evidence that something is absolutely impossible or cannot

2.modal verbB1
Definition

When you have strong evidence that something is absolutely impossible or cannot be true, you express this certainty with cannot. You are not guessing — you are drawing a logical conclusion. For example, if all the lights are off and nobody answers the door, you conclude that the person cannot be at home; if a friend just ate an entire pizza, you know they cannot be hungry again.

Example

Chidi cannot be at work today — I saw his car still parked at his house.

cannot + base verb (present deduction based on evidence)

You cannot be serious about quitting your job without a plan.

cannot + be (rejecting a possibility)

Common collocations
  • cannot be
  • cannot have
  • cannot possibly be
  • surely cannot
  • simply cannot be
Synonyms
  • must not

    less common; 'must not' more often expresses prohibition rather than deduction

  • could not possibly

    stronger and more emphatic

Antonyms
  • must

    the positive deduction form: 'He must be at home'

  • certainly

    adverb form conveying the same certainty

Grammar Patterns

cannot + base verb (present deduction)

cannot have + past participle (past deduction)

Usage Note

This sense expresses strong logical certainty, not possibility. The difference between 'He cannot be at home' (impossible, based on evidence) and 'He may not be at home' (possible but not certain) is important — the first is a firm conclusion, the second is a guess. For past events, use 'cannot have + past participle': 'She cannot have left already.'

Common Mistakes

You cannot be tired?' (question intonation — use 'can't' for questions).
Can't you be tired?' or 'Can't you be serious?
Cannot is not used in questions; use 'can't' instead.
He cannot be at home because I think he might be out.
He cannot be at home because his car is not in the driveway.
Use cannot for deduction only when the evidence is strong, not for guesses.

cannot — auxiliary verb

Word family

  • can
    modal verbA1
  • can't
    contractionA1
  • can't
    noun (only in phrases like "the can'ts")C2

Synonym discussion

Sense: modal verb/1

"Cannot" is the standard written negative form of "can," used in both formal and informal writing to express inability, lack of permission, or impossibility. "Can't" is the contracted form and is extremely common in everyday speech and informal writing, but it is generally avoided in formal academic or business documents. "Be unable to" is a more formal alternative that has the advantage of working in any tense — "could not" for past, "will be unable to" for future — whereas "cannot" is only used in the present tense. "Be not able to" is grammatically possible but less natural and less common than the other forms. For example: "I cannot attend the meeting tomorrow" (standard written English); "I can't make it to the meeting" (natural spoken English); "I was unable to attend last week's meeting" (past tense, where cannot/can't cannot be used).

cannot ↗can'tbe unable tobe not able to

Common collocations

Adverbs

Phrases

  • cannot help but
  • cannot afford to
  • cannot bear to

Etymology

Old EnglishMiddle EnglishEnglish

"Cannot" comes from the Old English verb "cann" (meaning "know how to" or "be able to") combined with "not." The two words began to be written as a single word "cannot" around the 1400s, making it one of the oldest contracted negatives in English. Unlike other modals whose negatives are written separately (like "must not" or "should not"), "cannot" fused into one word early on because "can not" was already pronounced as a single unit in everyday speech.