1.Neither John nor Mary has done their homework.
2.Neither John nor Mary has done his or her homework.
Which pronoun is suitable, singular or plural?
Learn English – Their or his or her in a sentence using “neither –nor”
pronouns
Related Solutions
Although there are many people that claim that "none" and "neither" should always take the singular form, it's always sounded odd to me, so I decided to dig into it a bit further.
For example, here is an Ngram of "none of us is" / "none of us are":
In this case, we can clearly see that "none of us are" - i.e. the supposedly "ungrammatical" form of the sentence was vastly more popular until roughly 1880. In 1880 or so "none of us is" began to take hold, and in the 1920s there was a steep decline in the use of "none of us are" - perhaps in response to overzealous copy editors enforcing the so called rule.
Most interesting is what's happened since the 1990s, where "none of us are" has shot back to prominence, leading to the fact that "none of us are" is now the dominant form again.
As suggested by snailplane, here's some interesting additional reading which seems to confirm my opinion that "none/neither should take the singular" is a wholly invented rule:
http://johnemcintyre.blogspot.co.uk/2010/01/with-malice-toward-none.html
http://motivatedgrammar.wordpress.com/2009/01/08/none-is-none-are-grammar-according-to-clarkson/
As a native speaker, I've always just gone with choosing the verb as if "none" or "neither" was not taking part in the verb choice.
The sentences are too long. -> None of the sentences are too long
A or B is the correct answer -> Neither A nor B is the correct answer.
Learn English – Which is more common? “Someone has left their bag” “Someone has left his or her bag”
All three sentences are acceptable in both written and spoken English, but each has slightly different meanings.
Using "their" indicates you don't know either the gender or number of people who left the bag on the table.
Using "his or her" indicates you don't know what gender the person who left the bag was, but you know (or assume) it was only one person.
Using "his" indicates you assume the (singular) person who left the bag is male.
If I were to guess the most common spoken usage for this I would personally use the sentence "Someone left their bag on the table."
Best Answer
To begin with, the second option is not possible here. The formula "his or her" is reserved for generic subjects, when you don't know or intend to specify the sex.
So is the first one okay? More or less. In most settings, you would use "their" in a case like this.
In higher registers (maybe as high as an academic paper), you would avoid "their" in this sentence. The solution would depend on the context. For example, if you're talking about the same class and the same assignment, you would probably say "the":
But if you couldn't do that, you might have to reword entirely:
That said, be aware that the correct use of "Neither ... nor" itself suggests a higher register. Hence, it doesn't jive very well with this use of "their". So you might reword it in a casual setting too.
One way of capturing the emphasis that "Neither ... nor" gives in a casual setting might be: