Which sentence is correct?

  1. The size of X and Y is the same.
  2. The sizes of X and Y is the same.
  3. The size of X and Y are the same.
  4. The sizes of X and Y are the same.

As a non-native speaker, my feeling is that 2) is totally wrong, and 1) and 4) are equally right.

  • 2
    The thing is that we'd almost always say X and Y are the same size, so all the examples sound a bit strange. Maybe you could invent some context that made them sound natural, I don't know. For me 2) and 3) are clearly wrong, 1) is weird but probably defensible, and 4) is completely grammatical but not very idiomatic. – JD2000 Jan 14 at 6:43

Setting aside whether it would be stylistically better to express the thought in some fifth way, and approaching this as a multiple-choice question, one can immediately rule out (2) and (3) as ungrammatical, because of the mismatch between the subject and the verb. This leaves (1) and (4), which are both grammatical. Each of the two is also defensible as making sense, but they, arguably reflect subtly different ways of conceptualising size(s).

One may think of size as something abstract that exists independently of the individual material things that instantiate it. One will then think of X and Y as instantiating that same one size, which makes (1) the best formulation.

Alternatively, one may think of sizes as something that exists only as sizes of particular things. According to this line of thinking, there is in this case only the size-of-X and the size-of-Y, which are the same; there isn't one abstract size that they both share. That favours (4).

Incidentally, the similar questions could be asked,a nd similar answers given, about various qualities other than sizes.

  • Agree that the sameness of the sizes confounds the issue a little here. If the sentence was "the sizes of X and Y are different", there'd be a strong case for the plural form, since we cannot be talking about one single size that's shared by X and Y - "the size of X and Y is different" would be incorrect. – Nuclear Wang Jan 14 at 16:35
  • Orwell says that we should reject even the arguably grammatical when it sounds unnatural. – Edwin Ashworth Jan 14 at 16:40

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