The Farlex Grammar Book > English Grammar > Parts of Speech > Verbs > Auxiliary Verbs > Modal Auxiliary Verbs > Modal Auxiliary Verbs - Can

Modal Auxiliary Verbs - Can

Definition

As a modal auxiliary verb, can is most often used to express a person or thing’s ability to do something. It is also used to express or ask for permission to do something, to describe the possibility that something can happen, and to issue requests and offers.

Expressing ability

Can is used most often and most literally to express when a person or thing is physically, mentally, or functionally able to do something. When it is used with not to become negative, it forms a single word, cannot (contracted as can’t). For example:

“John can run faster than anyone I know.”
“It’s rare to find a phone that cannot connect to the Internet these days.”
“We don’t have to stay—we can leave if you want to.”
“Can your brother swim?”
“I don’t think he can read.”
“Just do the best you can.”
“Can’t you just restart the computer?”
“When can you start?”

“Can do”

In response to a request or an instruction, it is common (especially in American English) to use the idiomatic phrase “can do.” This usually stands on its own as a minor sentence. For example:

Speaker A: “I need you to fix this tire when you have a chance.”
Speaker B: “Can do!”

Speaker A: “Would you mind making dinner tonight?”
Speaker B: “Can do, darling!”

The phrase has become so prolific that it is also often used as a modifier before a noun to denote an optimistic, confident, and enthusiastic characteristic, as in:

“His can-do spirit is infectious in the office.”
“We’re always looking for can-do individuals who will bring great energy to our team.”

We can also make this phrase negative, but we use the word no at the beginning of the phrase rather than using the adverb not after can, as we normally would with a modal verb. For example:

Speaker A: “Is it all right if I get a ride home with you again tonight?”
Speaker B: “Sorry, no can do. I need to head to the airport after work.”

Permission

We often use can to express permission* to do something, especially in questions (interrogative sentences).

For example:

“Can I go to the bathroom, Ms. Smith?”
“Can Jenny come to the party with us?”
“You can leave the classroom once you are finished with the test.”
“You can’t have any dessert until you’ve finished your dinner.”

(*Usage note: Although it is sometimes considered grammatically incorrect to use can instead of may to express permission, it is acceptable in modern English to use either one. Can is very common in informal settings; in more formal English, though, may is still the preferred modal verb.)

As a rhetorical device

Sometimes, we use can in this way as a rhetorical device to politely introduce or emphasize an opinion or sentiment about something, in which case we invert can with the subject. For instance:

“Can I just say, this has been the most wonderful experience of my life.”
“Can we be clear that our firm will not be involved in such a dubious a plan.”
“And, can I add, profits are expected to stabilize within a month.”

Note that we can accomplish the same thing by using the verbs let or allow instead, as in:

“Let me be clear: this decision is in no way a reflection on the quality of your work.”
“Allow us to say, we were greatly impressed by your performance.”

Adding angry emphasis

Can is sometimes used to ironically or sarcastically give permission as a means of adding emphasis to an angry command, especially in conditional sentences. However, this is a very informal usage, and it is not common in everyday speech or writing. For example:

“You can walk home if you’re going to be so ungrateful!”
“If he continues being so insufferable, he can have his party all alone!”
“You can just go to your room and stay there, young man! I’m sick of listening to your backtalk.”

Possibility and likelihood

Similar to using can to express ability, we also use can to describe actions that are possible. It may appear to be nearly the same in certain cases, but the usage relates less to physical or mental ability than to the possibility or likelihood of accomplishing something or of something occurring. For instance:

“You can get help on your papers from your teaching assistant.”
“My mother-in-law can be a bit overbearing at times.”
“People forget that you can get skin cancer from tanning beds.”
“It can seem impossible to overcome the debt from student loans.”

Negative certainty and disbelief

We use the modal verb must to express certainty or high probability, but we generally use can’t (or, less commonly, cannot) to express negative certainty, extremely low likelihood, or a disbelief that something might be true. For example:

“You can’t be tired—you’ve been sleeping all day!”
“I can’t have left my phone at home, because I remember packing it in my bag.”
“After three years of college, she wants to drop out? She cannot be serious.”

Making requests

It is common to use can to make a request of someone. For example:

“Can you get that book down from the shelf for me?”
“Your sister is a lawyer, right? Can she give me some legal advice?”
“Can you kids turn your music down, please?”

However, this usage can sometimes be considered too direct or forceful, and it may come across as impolite as a result. In more formal or polite circumstances, we can use other modal verbs such as could or would to create more polite constructions, as in: