(1)Computers are important research tools.

(2)Computers are an important research tool.

We can say that the first sentence treats computers as discrete objects.

The second sentence treats computers as a class or set of objects.

(3)Horses are useful animals.

(4)Horses are a useful animal.

We can say that the third sentence treats horses as discrete objects.

Why can't we say the fourth sentence treats horses as a class or set of objects?

  • 1
    To refer to horses generically, as a class, we might say "the horse is a useful animal" – Jim Mack May 3 at 14:38
  • What a good question! I feel it has something to do with a perception that a horse is a horse by virtue of having a horsey essence, of which there is only one, whereas a computer is a computer by virtue of what it can do, and doesn't really have an essence at all - certainly not one that is shared by all the others and thus defines what it is to be a computer. Not that I'd want to try to defend that perception philosophically, but language is based on an instinctive categorisation of things that doesn't / isn't supposed to hold up to rational scrutiny. – user339660 May 3 at 15:42
  • @Minty I think the difference is that in the first sentence the computers are treated as a single tool whereas in the second sentence the horses are referred to as 'animals'. If the first one said "Computers are important machines for research" then 'machines' has to be plural. If, on the other hand, the second sentence said "Horses are a useful resource" then the group noun can be singular. A computer is one machine and a horse is one animal but computers in general can be thought of as a single tool and horses in general can be thought of as a single resource. Compare like with like. – BoldBen May 3 at 18:06
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    @BoldBen The question does compare like with like - it asks how come we can say computers are an important research tool but not horses are a useful animal, when these sentences seem to be the same grammatically / syntactically (doesn't it?) I'm not sure how come, but am not seeing a difference in terms of syntax or grammar, which is why I was suggesting a semantic explanation. – user339660 May 3 at 18:36
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    I see no difference at all between the examples in terms of construction. You could just as easily say horses are important research tools or computers are a useful thing. I believe you're confusing the specific words with the syntax. – Jason Bassford May 3 at 20:11

I think sentence #4 does treat horses as the class of all horses, and that's exactly the problem with it.

It is possible for a class of objects to be a tool, if those objects collectively form a resource that is useful for accomplishing some task.

But it is not possible for a class of objects to be an animal, which is by definition a single living being. So sentence #4 is not grammatically wrong, it's simply nonsensical.

There is nothing inherently wrong with using horses as singular to refer to the class of all horses, so long as you use it in a context where that makes sense. You could certainly say something like:

Horses were an important method of transportation in the 19th century.

  • I agree, see my comments on the question. – BoldBen May 4 at 5:10
  • How do I know which words can be considered " a class of objects" – Chai Min Chun May 4 at 8:06
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    @ChaiMinChun In my opinion it is a matter of whether the word is inherent to the nature of a single member of the class or not. One horse is one animal, one computer is one machine, however many horses can be one resource and many computers can be one tool. Therefore 'resource ' and 'tool' can be classes but 'animal' and 'machine' cannot. – BoldBen May 4 at 11:25
  • @BoldBen Thank you so much. – Chai Min Chun May 4 at 15:15

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