Could and Can Role and Rules

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The words could and can are an essential part of the English language, widely used in various contexts. In this article, you will delve into the multiple ways 'can' and ‘could’ may be used.

What’s the difference between could vs can?

Understanding the subtle differences between 'can' and 'could' is essential for mastering the nuances of English language. These two modal verbs, while similar in many aspects, carry distinct meanings and are used in different contexts. This table aims to clarify these differences, providing learners with a clear guide on when to appropriately use each verb in various scenarios.

 Use of 'Can'Use of 'Could'
Basic FunctionExpresses ability or possibility in the present or future.Generally used to express ability or possibility in the past.
PermissionFormal or informal present or future permission.Polite request or permission, often more tentative.
PossibilityIndicates a higher degree of likelihood.Suggests a hypothetical or less certain possibility.
Requests and OffersInformal requests or offers.Polite, indirect or tentative requests or offers.
Conditional SentencesMay be used in zero conditional.May be used in the second conditional for hypothetical situations.
AdviceCan be used to give a direct advice.Can be used to give advice, often sounding less direct.

The choice between 'can' and 'could' significantly impacts the tone, formality, and meaning of a sentence in English. By carefully considering the context – whether it's about ability, permission, possibility, or politeness – speakers and writers can make precise and effective choices between these two modals. 

The use of can in the English language

Can is an English modal verb that may be used in various situations. Because of it’s versatile nature, can became a challenging word for English learners. Below, there are the rules how to use ‘can’ correctly.

Expressing Ability in Present

'Can' is frequently used to express:

  • general ability or the capacity to do something;
  • physical or mental ability;
  • contextual ability (speaking about the ability to do something a a particular moment).

In all the cases the structure is the same: ‘subject+can+verb+rest of the sentence.’ Here are some examples:

  • She can speak four languages. (general ability)
  • He can lift heavy weights. (physical ability)
  • I can see the stars tonight. (contextual ability)

‘Can’ is also used in describing what a machine or system is capable of doing. 'This software can process data quickly' highlights the capability of the software.

Indicating Permission and Giving Advices

'Can' is used to ask for or give permission in a more informal or casual context. 'Can I use your phone?' is a common way of seeking permission, whereas 'You can borrow my book' is an example of granting it. Sometimes, 'can' suggests a broader, more implied permission, often governed by rules or norms. For example, 'Students can use the library until 8 PM' indicates a policy-based permission.

'Can' is often used to offer casual or informal advice. For example, 'You can try this new restaurant for dinner' is a friendly suggestion without the force of strong recommendation. It also comes in handy when proposing possible solutions to a problem. 'You can restart your computer to fix the issue' provides a potential fix in a non-imposing way.

Denoting Possibility

'Can' helps express the possibility of something happening. For instance, 'It can rain in the evening' suggests that there is a chance of rain, but it's not certain. 'Can' is also used to warn about a potential risk or danger. 'Be careful, the surface can be slippery' alerts to the possibility of the surface being unsafe. In hypothetical scenarios, 'can' explores what is possible under different circumstances. 'If you save money, you can buy a car next year' illustrates a potential future outcome based on present actions.


The use of could in the English language

The modal verb 'could' is often used interchangeably with 'can,' yet has distinct applications. You should remember these difference to use each word correctly.

Expressing Possibility

One of the primary functions of 'could' is to indicate possibility. However, ‘could’ meaning in this terms is very different from ‘can.’ You should use ‘could’ to suggest possibilities that are hypothetical, speculative, or not certain. 

For instance, in the sentence, 'It could rain tomorrow,' the speaker isn't sure if it will rain, but acknowledges that it's a possibility. This form is particularly useful in scenarios where one wants to express uncertainty or speculate about future outcomes without asserting them as facts.

Polite Requests

When making a request, using 'could' adds a layer of politeness and deference. For example, 'Could you please help me with this report?' is more courteous and less imposing than saying, 'Can you help me with this report?' It shows respect for the other person's ability to decline the request without feeling pressured.

Past Ability

'Could' is the past tense form of 'can' and is used to talk about abilities someone had in the past but might not have anymore. For example, 'When I was younger, I could run a mile in under six minutes' implies that the speaker had the ability to run quickly in the past, which may or may not be the case presently. It's a way of recalling past skills or abilities that were once possible.

Conditional Situations

In conditional statements, 'could' helps to illustrate scenarios that are hypothetical or dependent on certain conditions being met. For example, 'If I had more time, I could learn to play the piano.' This indicates that the ability to learn the piano is contingent upon the availability of time, thus making it a conditional ability.

Suggesting Alternatives

'Could' can be used to suggest alternatives or options in a situation, often in the form of advice or recommendations. For instance, 'You could try calling customer service for help,' suggests an alternative action the person might take. It's a way of presenting options without asserting them as the only course of action.

Negative and interogative sentences

There’s no additional difference between can vs could in negative sentence or questions. Forming a negative sentence, you have to add ‘not’ after the word. Here are some examples:

  • I can not drive a car.
  • I couldn’t swim last summer, but now I understand some basics.

Forming ingterogative sentences, you just have to put can or could at the beginning of the sentence.

  • Can you bring me some wine?
  • Can you see the light?
  • Could you open the window?

Using could you vs can you, remember that the latter is more informal way to communicate. So pay attention to the context at the moment of speaking.


‘Can’ and ‘could’ are crucial parts of English language. They are used to express ability, possibility, make advices and requests, suggest alternatives - all of these things are communicated daily. Although they seem challenging, but you can master the rules for both words through practice.

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