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Which verb is grammatically correct when used to describe addition?

  • One and one are two.
  • One and one is two.
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There's a children's joke about this question in the U.S. "Do I say 'two and three is six' or 'two and three are six'?" "Neither: two plus three equals five!" – Peter Shor May 5 '14 at 21:05

It would be grammatically correct to use "are" if the subjects were indeed "two" individually, but they are not.

By saying "One and one are two," that means that each "one" is two. The equivalent would be, "One is two, and one is two."

Saying "One and one is two" groups "one and one" to be the subject of the sentence. And "one and one" is two. ;)

In your post, you said "which question is grammatically correct?" You would ask, "Is one and one two?" Although, that can be confusing without something to separate the "one" and the "two" at the end. The preferred method would be "Does one plus one equal two?"

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I'd note that "one and one are two" could also be okay if you assume some grammatically-key words were left out: "One and one[, combined, are equivalent to] two." Nonetheless, your answer is right on the money. – sraboy May 5 '14 at 18:59
What silliness to think of "one and one" as a singular noun! – Kyle Hale May 5 '14 at 23:02
@KyleHale, it's the single number "two" which the verb must agree with. – Phil Perry May 5 '14 at 23:22
@PhilPerry What? Verbs don't agree with objects. Dick and Jane has a dog Spot. – Kyle Hale May 6 '14 at 2:58
Hmm, I don't think that reasoning follows. If I say, "Bob and Mary are a couple", I don't mean that Bob is a couple and that Mary is a couple. I mean that taken together, the two are a couple. Or, "The engine and the transmission are connected." I mean that they are connected to each other, not that each is connected to itself. Etc. – Jay May 6 '14 at 13:45

Fluent English speakers routinely say it both ways.

The ever-popular Google ngrams shows that "one and one is" is significantly more popular, but "one and one are" is still common: https://books.google.com/ngrams/graph?content=one+and+one+is%2Cone+and+one+are&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cone%20and%20one%20is%3B%2Cc0%3B.t1%3B%2Cone%20and%20one%20are%3B%2Cc0

Logically, I think it should be "one and one are". By the normal rules of grammar, that is a compound subject. We wouldn't say "Bob and Charlie is ...", we say "Bob and Charlie are ..." Etc. @Snailplane's deleted answer -- I don't know why it's deleted, it seems a valid answer to me -- makes the interesting point that we sometimes use such compounds to refer to a single unit, like "Peanut butter and jelly is my favorite sandwich." I think the key there is that the words surrounding the "and" are a name or a title. Like of course we would say, "Pride and Prejudice IS Sally's favorite book", not "... are Sally's favorite book", because we're talking about one book whose title happens to have the word "and" in it. It's not like Sally likes a book called "Pride" and she also likes a book called "Prejudice". Do "one and one" in this sentence fall into that category? I don't think so.

Even when the point of a sentence is to say that two are more things are joined in some way, we still use "are". "Bob and Mary are a couple." "Smith, Jones, and Brown are a dangerous gang." "The four legs are what hold up the table." Etc.

So if you go by common usage, either is acceptable, but "is" is slightly preferred.

If you go by conventional rules of grammar, I think "are" is correct. Obviously others answering on here disagree with me. Which, perhaps, is why we see the split in common usage.

I think you should feel free to use whichever you prefer. In day-to-day usage no one is likely to even notice. If you have a teacher or an editor who insists that one is wrong, I'd just do whatever they ask for rather than argue about it.

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I wasn't really satisfied with my answer. It's a really complicated question to answer generally, I think. I was thinking that, because plural agreement is so common, it might be helpful to start from the assumption that plural is the default and explain the cases where singular is possible (or even required) as exceptions. – snail plane May 9 '14 at 2:43

I revise my previous comment to the OP. I don't think "is" is correct at all, though it is most often used (at least in America).

"He and she are a couple."

When using "and" to combine two singular nouns in the subject, you are supposed to use a plural verb. "And" conjoins while "or" does not.

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Either can be correct, but it depends on your context and meaning.

"One and one is two" is grammatically correct if you are using "and" to mean "plus" (addition). Adding the number one with the number one produces the number two, which is a singular thing, therefore "one and one" (one plus one) is singular.

A clearer (and thus arguably better) way to say this, however, would be "one plus one equals two".

On the other hand, "One and one are two" is grammatically correct if you are using "and" to mean "grouped with" or "put together". That is, "one (of these) and one (of those) are two (things put together)".

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"One and two are numbers." "One and two is three."

As others have pointed out, it depends on whether "one and two" are taken separately or combined. I'd say the grammar points strongly to "one and two is three", because "one and two /are/ three" suggests that one is three and two is three -- which is false!

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I would say that "is" could be correct, since the sentence "One and one is two" could be a truncated (or elided) version of "The result you get by adding one and one is two". "The result" is singular, therefore I would use "is."

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You just changed the subject of the sentence. "The result" is plainly singular. This doesn't apply to compound subjects combined with conjunctions. – sraboy May 7 '14 at 7:43

I would argue both are grammatically incorrect. One and one make two. Two things which can be combined together into a single thing are not that single thing. Red and blue are not purple, they make purple; hydrogen and oxygen are not water, they form water; and so on.

However, if you must, the only correct verb is are as your subject is a plural noun.

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Logic does not apply to grammar. "He and the dog are a dragon" is still grammatically correct. – sraboy May 7 '14 at 7:47

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