Couldn't vs Be unable to

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loverofenglish

Senior Member
Vietnamese
Hello!
At the meeting, even though he spoke well, he __________ persuade the other members.
A. was able to
B. could
C. couldn't
D. was unable to
The key is D but I am wondering why C isn't chosen, please?
 
  • srb62

    Senior Member
    British English
    Hello!
    At the meeting, even though he spoke well, he __________ persuade the other members.
    A. was able to
    B. could
    C. couldn't
    D. was unable to
    The key is D but I am wondering why C isn't chosen, please?
    C is possible in this sentence.
    However, I think D has been chosen as the correct answer to help learning.
    Sometimes couldn't/was unable to are interchangeable, but sometimes they are not.
    I think the idea here is to make you focus on the idea of trying to achieve a goal, but in the end not achieving this goal.
    I hope that makes sense, and I'd be interested to hear what others thought.
     

    loverofenglish

    Senior Member
    Vietnamese
    C is possible in this sentence.
    However, I think D has been chosen as the correct answer to help learning.
    Sometimes couldn't/was unable to are interchangeable, but sometimes they are not.
    I think the idea here is to make you focus on the idea of trying to achieve a goal, but in the end not achieving this goal.
    I hope that makes sense, and I'd be interested to hear what others thought.
    Thank srb62!
    But according to PEU by Michael Swan: In negative clause, and with negative or limiting adverbs like only and hardly, we use could to refer to one occasion.
    - I managed to find the street, but I couldn't find her house.
     

    geostan

    Senior Member
    English Canada
    I must admit that my first choice would be was unable to. Perhaps if you think of a corresponding affirmative sentence such as: At the meeting, he spoke well and was able to persuade the other members. Here could would not be possible. As to why, I'll have to give it some thought.
     

    kayokid

    Senior Member
    English, USA
    Hello. I agree that D is the best answer here. It is the best -- that doesn't mean it is the only possible answer. C is also possible in my mind -- but it doesn't sound as 'classy' as D. I can't explain it.

    Regarding the rule you quote in, 'I managed to find the street, but I couldn't find her house,'... It makes sense to me and the sentence sounds fine but I think I would just as easily have said, '... but I was unable to find her house.'
     

    phasting

    New Member
    English
    I couldn't and I wasn't able to are the same according to my Oxford dictionary. I don't know anyone who does not use them interchangeably.

    However, could and couldn't can also have the meaning, to have/not have permission to or to be/not be allowed to. For example, I wanted to go to the party but I couldn't because my parents won't let me stay out late on school nights.
     
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