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Usually 'is' can be an identity statement 'John is my boss' or a predication like 'John is angry', how about using 'is' for something that refers to no particular idea or object?

For example 'a computer is a device that performs computations', in this case we are not discusing any particular computer, and we are not simply discussing an idea because an idea is not 'a device that performs computations'.

Why is such a sentence correct? Can we use 'is' after a non-denoting phrase? Or should it be 'every computer is a device that performs computations' that way we can use the quantifier 'every' to confirm that 'is' is being used as a predicate.

Why can we have this new 'general' statement without use of a quantifier?

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    I’m voting to close this question because this is about the judgement on English usage and better placed at English Language & Usage.
    – Sir Cornflakes
    Jan 11 at 17:39
  • @SirCornflakes will put it there.
    – Confused
    Jan 11 at 19:29
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    Don't do it right now—an administrator can move it there together with the already available answer. But maybe the community decides to keep it here, it is just one out of 5 close votes cast.
    – Sir Cornflakes
    Jan 11 at 19:37
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    Are you really asking whether a computer is a device... is a correct English sentence? Or do you know that it is correct and do you want to know how it can be accounted for? In the latter case it might be better suited here; in the former, it belongs on another site. So please clarify whether you mean "Is such a sentence correct?" to be taken literally.
    – Keelan
    Jan 11 at 19:57
  • I know why, I'm just curious why it becomes a general statement without use of a quantifier.
    – Confused
    Jan 11 at 20:47

2 Answers 2

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This is called a gnomic sentence, expressing a universal truth about a relationship between predicates rather than a fact about a specific entity.

Similarly, consider the sentence "water freezes at 32 degrees Fahrenheit". We're not discussing any particular quantity of water, and we're also not discussing purely abstract concept (abstract concepts don't freeze). Rather, we're talking about water in general.

Logicians would probably use a universal quantifier to write out the meaning of these sentences, but that doesn't mean you need to say "every" in English. Languages have different ways of expressing gnomic sentences, and English uses the present tense. That's just how the language works.

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  • Why is it that it can become a general statement in this way without a quantifier? For example it is similar in structure to 'a man is outside' yet that is a specific, even 'I need a man' where 'a man' is not denoting it is singular in nature.
    – Confused
    Jan 11 at 20:49
  • @Confused The short answer is that gnomic statements can't generally talk about the location of something, since location is a property of individual entities. So as soon as you're bringing location into it, it can't be gnomic. Compare "a man is mortal" and "I like men", which don't refer to anyone in particular.
    – Draconis ♦
    Jan 11 at 21:14
  • My question is: Can a sentence like 'a man is a human' be used to discuss a specific individual? Or only in a general context? Is it simply pragmatics and convention or is there a linguistic reason that our first interpretation is one in generality? Can this sentence have two meanings?
    – Confused
    Jan 12 at 13:45
  • @Confused "A man is human" is general and gnomic, "The man is human" is specific (the context should make clear who "the man" refers to).
    – Barmar
    Jan 12 at 15:28
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    There's a fair amount of literature on Generics (aka Gnomics). The phenomenon of overgeneralization is a human universal, so there are generic clauses, sentences, verb phrases, and noun phrases. Bill walks to school, That dog bites, Sharon drives a Toyota/a 16-wheeler, The tiger is endangered, Tigers are endangered, *A tiger is endangered. They have special senses, constructions, affordances, and syntax. Some references here,, and here, and here.
    – jlawler
    Jan 13 at 0:17
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First, as Draconis's answer implies, the issue is not confined to predicates with is: you could ask the same question about sentences like A computer can't understand English.

The assumption in your question is that English phrases (or at least subject phrases) with the indefinite article necessarily denote some particular referent. The fact that such sentences are grammatical shows that the assumption is incorrect, and that such phrases can instead denote a generic member of the class.

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  • Can a sentence like 'a man is a human' be used to discuss a specific individual?
    – Confused
    Jan 12 at 13:46
  • @Confused Not felicitously, no -- at least, I can't think of a context in which it could.
    – TKR
    Jan 12 at 19:08
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    @Confused Yes, it can. We can use an indefinite article when the speaker is thinking of a specific individual, or thinking about one individual out of a group, but the identity of that individual has not been divulged to the listener. So, for example, if someone asks what you're doing you might say "I'm looking for a friend", where you mean a specific friend. For your given phrase, a scenario might be where there are a group of men, women and children who are all meant to be Zoobs, but a few of whom are might be human. One might say Bob thinks a man is human where the man is specific.
    – Araucaria - him
    Jan 13 at 17:55

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