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What is the difference in meanings and nuances between "capacity" and "ability" as in the following newspaper article in The Washington Post of today.

"Defense Secretary Chuck Hagel on Wednesday called the North Korean actions a “real and clear danger and threat” to the United States’ allies in the region, South Korea and Japan. “They have nuclear capacity now. They have missile delivery capacity now.”

…The Pentagon declined to specify where the systems would come from. “Though we do have a limited number of THAAD units available for deployment, we are quite confident in our ability to rapidly redeploy this system as dictated by threat levels,” said Defense Department spokeswoman Lt. Col. Monica Matoush."

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closed as general reference by FumbleFingers, tchrist, Waggers, Rory Alsop, Mitch Apr 4 '13 at 17:02

This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information.If this question can be reworded to fit the rules in the help center, please edit the question.

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You probably got the downvote because you could have just looked up the two words in a dictionary and then a thesaurus. –  user21497 Apr 4 '13 at 3:32
    
@Bill Franke: I closevoted for that reason, but then I decided it could present a problem for OP. Dictionaries normally only give the bare semantics and maybe a few examples. But probably most dictionary definitions of ability, capability, capacity will include both the other words anyway. The specifics of when and where capacity is idiomatically "valid" won't necessarily be clear. –  FumbleFingers Apr 4 '13 at 3:40
    
@Fumble: Yes, dictionaries & thesauruses are good as far as they go, but they don't know what's considered idiomatic at the moment or who considers X idiomatic and who considers it a solecism. I was merely speculating on the downvoter's motives. –  user21497 Apr 4 '13 at 3:56
    
    
possible duplicate of Difference between "ability" and "capability" –  Waggers Apr 4 '13 at 11:17

2 Answers 2

Strictly speaking, capacity is the ability to contain something, or amount which can be contained.

But it's occasionally (and inelegantly, imho) used in contexts where one would normally expect capability (essentially, a synonym for ability). It's worth noting usage figures from Google Books...

has nuclear capacity 14 results
has nuclear capability About 5,590 results

To me, one or two of those 14 results are actually valid - the ones that say things like...

The CT scenario has nuclear capacity of 326.4 GW in 2050.

...where "capacity" does indeed refer to an amount (that can be delivered, rather than contained). Similar usages include, for example...

This car assembly plant has a capacity of 1000 vehicles per day (i.e. - it can make that many).

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I.e, capacity is a Container Metaphor. –  John Lawler Apr 4 '13 at 13:54
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@John Lawler: I should have had the courage of my own convictions! I actually had the word "metaphor" in my original text, but I deleted it because I couldn't see how to succinctly explain what exactly is being metaphorically contained by a nation that has first strike capacity, for example. I suppose it's just that if you have xxxx capacity, that means you "contain" the ability to do [something important relating to] xxxx. –  FumbleFingers Apr 4 '13 at 15:29
    
Anything can be contained in a container metaphor, though it tends to be resources of some kind. After all, if a container can be a metaphor, so can anything else. It can contain the troops and weaponry to destroy a neighbor state, for instance, or the knowledge and technicians necessary to wipe computer systems somewhere else. There is a sense of cause and effect, measured in terms of alternative uses of whatever resources are in it. But it's not really ability -- ability has to be demonstrated, but this is all hypothetical. Capacity says nothing about probability; ability may. –  John Lawler Apr 4 '13 at 17:17
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@John: Gotcha! I'm happy enough with resourceful ... capable ... capacity. –  FumbleFingers Apr 5 '13 at 1:58

This is merely an example of a poor word choice in spoken English. Rather than capacity, Hagel should have used "capability" or "ability". However, as Thesaurus.com points out: "applied to a person, ability and capacity mean about the same thing but are grammatically different: an ability to do something, a capacity for doing something; ability is qualitative while capacity is quantitative; capacity refers to a general ability to comprehend an issue or perform a task; capability implies a reference to one of a set of such abilities".

When people speak spontaneously, they make mistakes. It's normal in every language. And what we say is not always what we would write. The spoken language is almost always more colloquial and informal than the written language; indeed, they are sometimes so different that they can be considered different dialects, and readers usually have different expectations about what others write and say. We usually expect written English to be much more precise and correct than spoken English; however, our expectations are frequently unmet.

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