The Modal Verb "Can" in English

"Can" is one of the most common modal verbs in English. Modal verbs are auxiliary verbs that express ability, possibility, permission, or obligation. "Can" is primarily used to express ability, possibility, and permission, making it an essential verb to master in English communication.

Unlike regular verbs, modal verbs like "can" have special characteristics: they don't change form with different subjects, they're followed by the base form of the main verb (without "to"), and they don't use auxiliaries to form questions or negatives.

1. Form and Structure

The modal verb "can" has the same form for all subjects in the present tense:

  • Affirmative: Subject + can + base verb
  • Negative: Subject + cannot/can't + base verb
  • Question: Can + subject + base verb?

Examples:

  • I can swim.
  • You can speak three languages.
  • He can play the piano very well.
  • She cannot (or can't) drive a car.
  • It can rain heavily in this region.
  • We can finish this project on time.
  • They cannot (or can't) attend the meeting tomorrow.
  • Can you help me with this exercise?

2. Conjugation Table for Present Tense

Here is how "can" is conjugated with different subjects in the present tense:

Subject Affirmative Negative Question
I I can swim I cannot/can't swim Can I swim?
You You can swim You cannot/can't swim Can you swim?
He He can swim He cannot/can't swim Can he swim?
She She can swim She cannot/can't swim Can she swim?
It It can work It cannot/can't work Can it work?
We We can swim We cannot/can't swim Can we swim?
They They can swim They cannot/can't swim Can they swim?

Note that "can" does not change form regardless of the subject.

3. Main Uses of "Can"

1. Ability: To express physical or mental abilities.

  • She can run a marathon in under 4 hours.
  • I can speak French fluently.
  • My grandmother can knit beautiful sweaters.

2. Possibility: To express that something is possible or may happen.

  • It can be very cold in winter here.
  • Traffic can be terrible during rush hour.
  • Climate change can affect agriculture.

3. Permission: To ask for or give permission (informal).

  • Can I use your phone?
  • You can take an extra day off if you need it.
  • Students can use calculators during the exam.

4. Requests: To politely ask someone to do something.

  • Can you open the window, please?
  • Can you tell me the way to the station?
  • Can you help me with this heavy bag?

5. Offers: To offer to do something for someone.

  • I can give you a ride to the airport.
  • We can help you move into your new apartment.
  • I can lend you some money if you need it.

4. Past Form: "Could"

The past form of "can" is "could." It's used to talk about past abilities, possibilities, and requests.

  • Past ability: When I was younger, I could run very fast.
  • Past possibility: It could be very hot in summer.
  • Polite requests: Could you pass me the salt, please?
  • Suggestions: We could go to the movies tonight.

For the negative form in the past:

  • I could not (or couldn't) understand what he was saying.
  • They could not (or couldn't) attend the wedding last Saturday.

5. Differences Between "Can" and Other Modal Verbs

It's important to understand when to use "can" versus other similar modal verbs.

"Can" vs. "May":

  • Can is more informal and commonly used for permission: Can I go to the party?
  • May is more formal for permission: May I have your attention, please?

"Can" vs. "Could":

  • Can refers to present ability or possibility: I can help you now.
  • Could refers to past ability: I could speak Chinese when I lived in Beijing.
  • Could is also used for more polite requests: Could you help me? (more polite than "Can you help me?")

"Can" vs. "Be Able To":

  • Can is used in present and past simple tenses only.
  • Be able to can be used in all tenses and with other modal verbs:
    • I will be able to speak German after my course.
    • She has been able to solve the problem.

6. Common Expressions and Idioms with "Can"

There are several common expressions and idioms in English that use the modal verb "can":

  • "As much as you can" - to your maximum capacity
  • "Can't help it" - unable to control or stop something
  • "I can't believe it!" - expressing surprise
  • "Can do attitude" - positive, ready-to-act mindset
  • "You can say that again" - strong agreement
  • "Can't stand" - strongly dislike

Examples:

  • Take as much as you can carry.
  • I'm sorry for laughing, but I can't help it.
  • I can't believe you won the lottery!
  • She has a can-do attitude toward everything.
  • "This weather is awful." "You can say that again!"
  • I can't stand people who talk during movies.

7. Common Mistakes with "Can"

Here are some common mistakes to avoid when using "can":

1. Using 'to' after 'can':

  • ❌ I can to swim.
  • ✓ I can swim.

2. Using 'do' or 'does' with 'can' in questions or negatives:

  • ❌ Do you can dance?
  • ✓ Can you dance?
  • ❌ She does not can ride a bike.
  • ✓ She cannot (or can't) ride a bike.

3. Using 's' with the main verb after 'can':

  • ❌ He can plays the guitar.
  • ✓ He can play the guitar.

4. Confusing 'can' and 'could' for making requests:

  • 'Could' is generally more polite than 'can' for requests.
  • ✓ Can you close the door? (slightly less polite)
  • ✓ Could you close the door? (more polite)