Can is the most common modal verb in English. It combines with the base form of another verb to express ability, permission, possibility, or a request.
Like all modal verbs, can has no -s in the third person, no infinitive, and no -ing form. It is always followed by the bare infinitive — the verb without to.
Form
| TYPE | STRUCTURE | EXAMPLE |
|---|---|---|
| Positive | subject + can + verb | James can cook. |
| Negative | subject + cannot / can't + verb | I can't swim. |
| Question | Can + subject + verb? | Can she speak French? |
The full negative form is cannot — written as one word, not two. In speech and informal writing, can't is far more common.
Can does not change with the subject. Whether the subject is I, he, they, or it, the form stays the same.
Ability
The most frequent use of can is to describe what someone knows how to do or is physically able to do right now.
Can often appears with perception verbs — see, hear, smell, taste, feel — where many other languages would use a simple present tense instead.
Permission
In everyday conversation, can is the standard way to ask for or give permission.
Some grammar books insist on may for permission, but in modern spoken English, can is perfectly natural in all but the most formal situations.
General possibility
Can describes things that are sometimes true or generally possible, without referring to one specific moment.
This is not about one event — it is about what is possible in general. For a specific future event, English uses could or might instead.
Requests
A question with can you... is one of the most common ways to ask someone to do something.
These are not questions about ability — the speaker already knows the listener is able to do it. The question is a polite way of asking them to act.
Can't for impossibility
When something seems logically impossible based on evidence, English uses can't (or cannot in formal writing).
This is not about ability. The speaker is saying the situation is impossible given what they know. It works as the strong negative counterpart of must — where must means "I'm almost sure this is true", can't means "I'm almost sure this is not true".
Can and could
Could is the past form of can when talking about ability.
Could is also used for more polite requests — slightly softer than can.
The full comparison between can and could is covered separately.
Can and be able to
Can has no infinitive and no future form. When you need can in a tense where it does not exist, use be able to instead.
In the present tense, can and be able to mean the same thing, but can is far more natural in everyday speech. The full range of be able to is covered separately.
Common mistakes
Missing base form
Adding -s to the verb after can
Using do/does in questions and negatives
Writing cannot as two words
Using will + can for the future