Understanding the Difference Between “Could” and “Can”

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  • Can and could are modal verbs that express possibility or ability. They’re also used to make a request or ask for permission.
  • When referring to ability or possibility, can is used for present scenarios, whereas could is used in the past tense.
      • ○ I can translate that for you.
      ○ I could have gone to Harvard, but I preferred to attend Howard University instead.
  • When you’re talking or writing about the future, use can when referring to something that is certain (or very likely) to happen. Could implies that something might happen in the future, but there’s still a possibility it won’t.
      • ○ You can get an infection if you keep picking at your wound.
      ○ You could win first place in the marathon if you keep up with this rigid training schedule.
  • Both could and can are used to ask for permission; however, can is often considered colloquial and could is seen as more polite.
      • ○ Can I be excused?
      ○ Could you help me find my keys, please?

What Is the Difference Between “Can” and “Could”?

Can and could are both modal verbs. Modal verbs are the type of auxiliary verb that indicate suggestion, obligation, possibility, or ability. In addition to can and could, modal verbs also include:

There are a few others such as must and ought to. Additionally, need sometimes functions as a modal verb.

LanguageTool's Grammar Checker can help you fix mistakes in sentences containing modal verbs.

When To Use “Can”

Here are the different uses of can:

1. Using “can” to express a strong possibility or indicate that something is certain to happen

A bee sting can cause pain and discomfort.

2. Using “can” to indicate ability

I can run a mile in under eight minutes.

3. Using “can” to make a request

Can you upload the document onto the hard drive, please?

4. Using “can” to ask for permission

Can I go to the restroom, please?

It’s important to note that using can to ask for permission is considered informal and colloquial. It can also be seen as ambiguous. Some people may read this question as if you’re questioning whether you’re capable of going to the restroom. The more appropriate modal verb to use in this instance would be may.

May I go to the restroom, please?

Can has two negated forms: Cannot is spelled without a space in between, and can’t is considered as a bit more informal.

When To Use “Could”

Could has similar uses, but there are some differences to keep in mind. We’ll review them below.

1. Using “could” to express possibility

The main difference between could and can is that when expressing a possibility, could implies that something might happen, but there’s still a doubt.

I could buy a new car by the end of the year if I save up enough money.

2. Using “could” to indicate possibility or ability in the past

I could have helped her had I known she was struggling.
Larry could swim by the age of three.

3. Using “could” to make a request

Could you lower the volume?

4. Using “could” to ask for permission

Could I work a few extra hours this week?

Again, may would be the grammatical correct modal verb to use in this scenario. However, when it comes to can and could, could is often considered the more polite word to use. Its negation is could not or couldn’t.

“Could” vs. “Can”

Understanding the difference between “could” and “can” may be challenging. The most important things to remember are:

  • Can is used when referring to something with a strong possibility or occurring, whereas could is used to refer to something that has a weak possibility.
  • Both can and could can be used to make a request, but when asking for permission, could is the more polite choice to use.
  • When indicating ability or possibility, can is used in the present tense and could is used in the past tense. For example:
When I was young, I could only write clearly in one language, but now thanks to LanguageTool, I can write clearly in multiple languages.