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A grammar book says that in the following sentences we must not use "could" instead of "was/were able to".

  • The fire spread through the building very quickly, but everyone was able to escape.

  • They didn't want to come with us at first, but finally we were able to persuade them

However, when I searched the English language corpus COCA by "finally could", I found some counter-examples. Here are two examples from COCA.

  • I told her to get in line. Did it make you feel better? It did. I finally could say something.

  • Then, when it ended and I finally could get my family back, it came at a price, like suddenly being blind.

Are these examples grammatically incorrect?

Edit(Jun. 5, 2014) I posted the same question here.

  • I just wrote a lengthy answer about the nuance of "could have" vs. other expressions, on another question. You may have been instructed against using "could" because of those reasons. – Codeswitcher Jun 3 '14 at 22:42
  • @Codeswitcher not sure that it applies - in those first two examples, I think the difference is using could implies capability, where as was/were able to implies that it was actually done. – jimsug Jun 3 '14 at 23:33
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    I don't know the grammar rules, but I know those last two examples don't seem right to me. "I could finally say something." seems more correct. – Greg D Jun 4 '14 at 0:13
  • @GregD The occurrences in COCA are: "finally could" 41 "could finally" 341 – Makoto Kato Jun 4 '14 at 0:19
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I believe that you could replace every were able to in your examples with could, but it might not mean what you think it means, and it could sound strange or misleading enough that some grammar books make it a rule that you must not use it. For example,

11.12.3 Specific achievement in the past
Could cannot normally be used when we are describing the successful completion of a specific action: was/were able to, managed to or succeeded in + -ing must be used instead.

In the end they were able to rescue the cat on the roof.
In the end they managed to rescue the cat on the roof.
In the end they succeeded in rescuing the cat on the roof.
--Longman English Grammar, L. G. Alexander

However, I think this is a little too simplified, and it could cause confusion, even for advanced learners. In my opinion, it is easier to think that

  • could suggests the possibility to do the action, but they probably did not do it, while
  • was/were able to suggests that they could do it, and they did it successfully.

And because of that, was/were able to is preferred when we are talking about the successful completion of a specific attempt. Though I believe that this might not be a hard-and-fast rule. The was/were able to always suggests that it's very likely that the attempt was successfully made. The managed to and succeeded in also suggests so, and the achievement is even more definite.

Let's consider the examples:

The fire spread through the building very quickly, but everyone could escape.
The fire spread through the building very quickly, but everyone was able to escape.
(Both versions suggest that they had a chance to escape, but only the second suggests that they really made it, safely.)

They didn't want to come with us at first, but finally we could persuade them.
They didn't want to come with us at first, but finally we were able to persuade them.
(Both versions suggest that we had a possibility to persuade them, but only the second suggests that we really persuaded them, successfully.)

Now the examples from COCA,

I told her to get in line. Did it make you feel better? It did. I finally could say something.
(This means that "I" finally had a chance to say something. Did "I" say something? Maybe, maybe not. Though it sounds likely that "I" did say something. It might not be so.)

Then, when it ended and I finally could get my family back, it came at a price, like suddenly being blind.
(What the text really states is that "I" finally had a chance to get "my" family back. Though it sounds likely that "I" did really get the family back. It might not be so.)

This should answer your question "Are these examples grammatically incorrect?".
Of course not. They are grammatically correct.

  • Of course, could can refer to "one occasion" with certain verbs. Example: I could smell something burning. – M.N Jun 4 '14 at 7:19
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    If it were possible for you to smell something, obviously, you would really smell it. Some grammar books write explicit rules for sense verbs, but I think they're unnecessary. – Damkerng T. Jun 4 '14 at 7:30
  • I guess the point is whether "could" can refer to "one occasion" or not. That's what my example supports. – M.N Jun 4 '14 at 7:48
  • M.N. I think the point of the question is that, "can we use could with what seems like "the successful completion of a specific action" or not (which grammar books say that "we must use was/were able to instead, and the OP already knows this). – Damkerng T. Jun 4 '14 at 15:47
  • @M.N That's right. I believe that the OP got those two sentences from a grammar book, like you got a few from PEU, and I found a few in LEG. They might phrase the same rule a little differently, but essentially, they suggest that we should not use was/were able to (and should use must) for this kind of action (or according to PEU 122.5, "somebody did something on one occasion"). – Damkerng T. Jun 4 '14 at 16:46
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"Could" is used to talk about "general ability" - for example to say that somebody could do something at anytime, whenever he/she wanted.

Example: When I was younger, I could run 10km in under 40 minutes.

However, it is not normally used to say that somebody did something on one occasion. Instead, other expressions are used. Example:

  1. How many eggs were you able to get?

  2. I managed to run 10km yesterday in under an hour.

  3. After six hour's climbing we succeeded in getting to the top of the mountain.

  • I searched COCA by "could finally". It hit 341. One of which is: "As the dirty hair was cleared from the face, Michael could finally see the eyes staring back. They looked at him with a mix of emotion: fear and anger, shame and rage." This seems to be a counter-example. – Makoto Kato Jun 4 '14 at 13:22
  • @ Makoto Kato: With certain verbs (see, hear, understand, smell, taste, remember, guess), "could" can be used to refer to an occasion that happened once. That's why I've used normally in my answer. – M.N Jun 4 '14 at 14:08
  • Is there a way to recognize those exceptional verbs(see, hear, etc.)? – Makoto Kato Jun 4 '14 at 14:27
  • @MakotoKato If you have Swan's Practical English Usage, you can find M.N. three examples and the mentioning of certain verbs in two sub-entries 122.5 past: could is not always possible, and 125.1 is about verbs refer to perception (such as see, hear, feel, smell, taste). Also, be aware that these are only two sub-entries listed under five main entries related to can and could, 121-125. – Damkerng T. Jun 4 '14 at 15:40
  • As far as I know, there are only a number of them, those I've already mentioned. So recognising them shouldn't be a problem. – M.N Jun 4 '14 at 15:44

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