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Can/could vs. to be able to Posted by on Oct 30, 2013 in English Grammar

The use of ‘can/could’ and ‘to be able to’ in order to express ability, can at times cause confusion. So, today we are going to look at these different verb constructions and how they are used the same, and differently, to talk about ability. Here we go.

Can and to be able to are usually used in the same way without a difference in meaning, but not always…

Can’ is a modal auxiliary verb that expresses general ability in the present tense; ‘could’ works the same way, but in the past tense.

To be able to’ is not a modal auxiliary verb. It is the conjugated verb ‘to be’ + the adverb ‘able’ + the infinitive ‘to’.

When talking/writing about ability in the present tense you can use either ‘can’ or ‘be able to’, but ‘can’ is generally more common among native speakers.

Examples:
I can speak two languages.
I am able to speak two languages.

When talking/writing about past ability you can use ‘could’ or ‘was/were able to’ in order to discuss an ability that existed for a long time, but now no longer exists.

Examples:
When I was young, I was able to speak two languages.
When I was young, I could speak two languages.

But you should only use ‘was/were able to’ with action verbs to talk about an ability related to a single event or incident in the past.

Examples:
I was able to surprise my teacher yesterday.
Don’t say: I could surprise my teacher yesterday.

You can use either ‘could’ or ‘was/were able to’ with some stative verbs (see, hear, feel, taste) to discuss ability related to a single event or incident in the past.

Examples:
I was able to see the teacher well from my seat yesterday.
I could see the teacher well from my seat yesterday.

It is also okay to use ‘couldn’t’ or ‘wasn’t/weren’t able to’ for negative statements for both single events and a long period of time in the past.

Examples:
I wasn’t able to surprise my teacher yesterday. or I was never able to surprise my teacher.
I couldn’t surprise my teacher yesterday. or I couldn’t ever surprise my teacher.

Lastly, when talking/writing about future ability in English we only use ‘will be able to.’ We never use ‘can’ for an ability that may exist in the future.

Examples:
When I finish the advanced level English class I will be able to speak like a native speaker.
Don’t say: When I finish the advanced level English class I can speak like a native speaker.

But it is okay to use either ‘can’ or ‘will be able to’ when we are talking about decisions and future arrangements.

Examples:
I can attend the class next week.
I will be able to attend the class next week.

I hope this post helps clear up any confusion you had about the different uses of ‘can/could’ and ‘to be able to’ when you are talking about present, past, and future ability.

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About the Author:Gabriele

Hi there! I am one of Transparent Language's ESL bloggers. I am a 32-year-old native English speaker who was born and raised in the United States. I am living in Washington, DC now, but I have lived all over the US and also spent many years living and working abroad. I started teaching English as a second language in 2005 after completing a Master's in Applied Linguists and a Certificate in English Language Teaching to Adults' (CELTA). Since that time I have taught ESL in the United States at the community college and university level. I have also gone on to pursue my doctorate in psychology and now I also teach courses in psychology. I like to stay connected to ESL learners around the world through Transparent Languages ESL Blog. Please ask questions and leave comments on the blog and I will be sure to answer them.


Comments:

  1. Margaret Nahmias:

    Can and to be able to are pretty much interchangeable expect when to talking about the future.

    • gabriele:

      @Margaret Nahmias Thanks for your comment. Yes, this is generally true. I just went into more detail about different uses in the post to show some of the subtle differences.

  2. Glaucio:

    Thanks for your tips. In fact, I’m studying English badly. I have more doubts. I believe that I’ll learn this idiom, though. I’ll try to access your blog many times….! Thanks again !

  3. Tsotsi:

    Hello
    I was just wondering if this sentence ” We could go sailing yesterday bc the weather wa so nice.” is incorrect bc we cannot use could with posibility in the past and it should be ” could have gone”. What about “We could go sailing.” ? Is it correct and what time it refers to ? And the same question for “We can go sailing.”

    • gabriele:

      @Tsotsi Hi Tsotsi,
      Great questions. Let’s look at each of your sentences in turn.
      “We could go sailing yesterday bc the weather was so nice.” – This sentences is not 100% correct as is, but you are on the right track as to why it isn’t correct. If you want to talk about the past you could say “We could have gone sailing yesterday because the weather was so nice.” So, in this sentence you need to use the past tense “have gone” instead of “go” to talk about the past.
      Your second sentence example “We could go sailing.” is a grammatically correct sentence. I refers to the present or future.
      Your third sentence “We can go sailing.” is also grammatically correct an is also good to use for talking about the present or future.
      I hope that helps.
      Gabriele

  4. Nina:

    In my family (from central Missouri) we use the phrase “might could” when other people say “might be able to”. Do you know if this is a holdover from how folks spoke in Ireland before the 1900s?

  5. Sumith:

    Some non natives use sentences like ‘ I could be able to do it ‘ Is this right . i think this is a wrong repetition of a meaning . I think it should be either’ I was able to do it ‘ or I could do it .
    Further how can a teacher gives ideas bc users use arbitrary ideas! Teachers can only explain existing word orders.