“Can” vs. “Could”: What’s The Difference?

It can be easy to mix up can with could. Can you use these words interchangeably or not?

In this article, we’ll explain the differences between can and could, cover when and how both words should be used, and provide examples that show how they’re typically used in sentences.

Quick summary

The verb can is an auxiliary (helping) verb that is often used alongside other verbs to express ability, possibility, or permission (in the case of permission, could is often considered more polite than can, but they are grammatically interchangeable in this context). Because can is an irregular verb, its past tense form is could, as in Back then I could not do it, but I can now. Could is also used to form hypothetical or conditional statements (in what’s called the subjunctive mood), as in If you could have any superpower, what would it be?

When to use can or could

The word can is an auxiliary verb (or helping verb) and a modal verb. It is commonly used together with other verbs to express ability, possibility, or permission (asking and giving).

For example:

  • I can speak French fluently. (ability)
  • The coin can land on heads or tails. (possibility)
  • Can I have some water, please? (permission)
  • Sure, you can have some water. (permission)

The simple past tense form of can is could. Could is also used in the context of ability, possibility, or permission. In the case of possibility, the present perfect tense is typically used. In the case of permission, could is typically only used when asking permission, not giving it.

For example:

  • I could speak French fluently when I was younger. (ability)
  • The coin could have landed on heads or tails, and fortunately for you it landed on heads. (possibility)
  • Could I have some water, please? (permission)

When asking for permission, could is often considered to be more formal or more polite than can. Grammatically, though, either one is completely acceptable.

The word could is also often used for the subjunctive mood, which is used to express hypothetical or conditional statements. When used this way, could is used to express conditional or hypothetical ability or possibility even when talking about the present or the future. When discussing the past in this context, the word could is often used alongside the auxiliary verb have.

For example:

  • If you really tried, you could easily pass the test tomorrow.
  • Being lost is bad, but it could be worse—we could still be in the woods.
  • She could have been the champion if her opponent hadn’t cheated.

Like other auxiliary verbs, can and could often appear alone in sentences. In this case, they are still acting as auxiliary verbs—the main verb is omitted but still understood.

In these examples, the omitted verb or verb phrase is included in brackets for clarity:

  • Cheetahs can run faster than lions can [run].
  • I can’t play piano, but my brother can [play piano].
  • I’m not going to punish you, even though I could [punish you].

For a related comparison, check out our guide to can vs. may.

Verbs similar to can and could

There are two other auxiliary verbs whose conjugations are similar to can and could. The past tense of the verb will is would and the past tense of the verb shall is should.

Examples of can and could used in a sentence

Let’s look at examples of sentences that show how can and could are typically used.

  • Parrots can imitate human speech.
  • To reach the castle, we could either use the mountain path or the forest trail.
  • Do you think Batman could beat Superman in basketball?
  • Could you tell me which one is more expensive?
  • Can I please use your phone?
  • They could be the champions if they can start to get along.

Take The Quiz

Feeling confident about how much you’ve learned about these verbs? If so, show off how capable you are by taking our quiz on can vs. could. You may surprise yourself with what you’ve learned!

Learn more about modal verbs like "can" and "could" here.

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