While working on a standardized test, where one of the questions suggests to choice the only one correct answer, the following sentence seems to me a bit confusing:

Long hours and unsociable shifts _____ take their toll on health, relationships and family life.
A (must)
B (are able to)
C (can)
D (shouldn't)

The only correct answer for this question is C. However, it seems to me that B is also possible. As far as I understand, "can" is preferred here because it is used more frequently and the question is more about general capability. But these arguments are not seem strong enough to claim C as the only right answer.

So I am asking if you can clarify why this answer is so preferable and if you can "give a taste" about how much unnatural is B variant sound.

  • Are you certain C is marked as correct? I ask since there is a rule: If two answers are identical, they must both be wrong. 'Can' and 'be able to' mean the same thing. The fact that 'can' is more common doesn't make it better. I like answer A - must best at making the most compelling statement, but it would help to see the whole paragraph to see what sets up this sentence. (In math, compare that if 4 and 4.00 show up as answers when neither format is called for, they are both wrong. However, 1/2 is a better answer over 2/4 because of the rule to simplify fractions.) Commented Mar 31, 2017 at 18:32
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    Though can and be able to are synonymous, this does not mean that they are fully interchangeable. For instance, it's obvious that 'a bruised rib can be painful' cannot be rendered 'a bruised rib is able to be painful'. When 'can' is replaceable by 'may', it may not be replaceable by 'be able to'. // Actually, B is the only answer I think is certainly unacceptable. Commented Mar 31, 2017 at 18:41
  • @YosefBaskin Yes, C is marked as the only correct. As for me, A seems to be too inescapable, these hours do not necessarily lead to such consequences. There is no whole paragraph, it is a standalone sentence. Commented Mar 31, 2017 at 18:56
  • @EdwinAshworth Thank you, the rule with 'may' seems to be quite reliable. Commented Mar 31, 2017 at 18:59
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    @Yosef Baskin The two answers B & C are by no means identical. 'Can' and 'am/are/is able to' are often, but not always, interchangeable. And they're not interchangeable here. Commented Mar 31, 2017 at 21:31

2 Answers 2


Long hours and unsociable shifts are not able to act on their own in taking their toll on health, relationships and family life.

They require a person subject to health, relationships and family life. Therefore the most logical answer is C. A and D are non-relevant or opinionated.

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    But they are grammatically acceptable, and could be used in certain contexts. ELU is not a forum where the accuracy of pronouncements is weighed, but where the legitimacy of the phraseology is weighed. Commented Mar 31, 2017 at 21:53
  • I support what Veiss is saying, precisely in terms of the legitimacy of the phraseology. For something to "be able to", the thing must be an active agent that wants to do something. A hurricane can uproot a tree, the earth can produce plenty or withhold its harvest, and long hours can take their toll, but only living beings are able to do anything. Commented May 30, 2017 at 21:56

It should be noted that be able to denotes ability only whereas ability is not the only meaning of the modal can. For example, it can mean possibility and permission depending on context.

The context of this test question allows not ability but possibility in the blank. Therefore, choice B is incorrect, while choice C is.

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