Can and Could: What’s the Difference?

Can and could seem confusing, but they are really just two versions of the same verb. Here is how to tell them apart.

The verbs can and could may seem like similar words, but these modal verbs have slightly different uses. Strong writers are those who can learn to use them well. As you strive to learn English, here is what you need to know to distinguish between can and could.

Definition of Can and Could

Before looking at the different ways to use can and could in English grammar, first you must define the words. Can and could are two forms of the same verb, which means to be able to or permitted to do something.  

Can and Could Are Modal Auxiliary Verbs

Both can and could are a type of verb known as modal auxiliary verbs. These are used to show the capability or possibility of something. 

When a base verb and modal auxiliary verb get paired together, the base verb does not change form based on the number, tense or voice of the sentence. For example, both of these are correct:

• He gives his children an allowance.
• He could give his children an allowance.

When paired with a helping verb, the base verb give does not change, even though the subject is singular. 

Can Expresses Present Tense

The word can will express possibility, general ability or permission, but always in the present tense. You could say:

• He can speak two languages.

This is a present tense fact. You can also say:

• Eating healthily can help you lose weight.

This is also a fact that happens right now. 

Can Used for Making Informal Requests

If you make a request, both can and could are appropriate. However, can is the form of the verb to use in informal speech. You could say:

• Can you come here, please?

This request is made in the present tense and is informal. 

Other Uses of Can

Can is also used to make an offer. If you say:

• Can I show you where to put your coat?

You are using the verb properly. 

Can is also used in its negative form to show that an action is not allowed. This use of can is always paired with the word dot, as in:

• You cannot leave your coat there.

Could as the Past Tense of Can 

Could is the past tense of can. In this use, it can mean ability or possibility that took place in a past time. You could say:

• He could speak fluently when he was younger.

You could also say:

• That mistake could have been prevented.

Could Used for Making Formal Requests

Could, like can, is sometimes the word chosen when making a request. it is the more formal or polite form of the verb. For example, you could say:

• Could you come over at 7 p.m. instead of 8?

This is a polite request, not an informal one. 

Could to Show a Suggestion or Future Possibility

The word could can show the suggestion of an action in conditional sentences. For example, you might say:

• I could run a marathon if I put in several months of training.

This sentence implies you could only perform the action if a condition, the training, occurs. In this way, it is a future possibility, but only on condition.

Examples of Can and Could

Here are some examples of can used properly:

• I can ride a bike easily. (This sentence states that you are able to ride a bike.)
• Can the children go to the park without an adult? (This sentence is asking permission to go to the park unsupervised.)
• You can go to your friend’s house after school. (This sentence delivers permission to go to the house.)
• Working hard can get you a raise at your job. (This use expresses the possibility of an action.)
• Could you please raise your hand before you speak? (This is a polite request.)
• He could visit his grandmother over Christmas break. (This shows the possibility of a visit.)
• The police officer could have written me a ticket, but he chose to give me grace. (This shows the ability of the officer to write the ticket.)

Can and Could Used in Passive Voice

A final use of the modal verbs can and could is in the passive voice. When the verbs get paired with a form of the word be and the past participle of a verb, it is a form of passive voice. Here is an example:

• The furnace could be repaired, but the price is high

In this sentence, the furnace does no action, and thus it is the passive voice. 

A Final Word on Can and Could

When it comes to grammar rules, can and could are fairly easy to remember once you understand them. Can represent a present ability or present possibility. It is a more informal use when asking for permission.

Could, on the other hand, is the past form of can. It can also show future possibilities in conditional statements. It is the way to ask polite questions or to ask for permission in a more formal manner.

FAQs About Can and Could