The exception is when we want to use someone and follow it by the plural pronoun (they or them), as in, for example, If someone has an accident, make sure you stay with them until help arrives. When I first wrote this sentence, I tried saying make sure he or she…, but the paragraph became long and ugly. So then I tried a plural: If people have accidents, make sure…. But the image of many people having accidents all around you at the same time seemed unlikely. So I ended up with If someone has an accident, make sure they… . It’s what we do in normal speech. It’s what many great writers have done, too, including Jane Austen. You will offend a few readers, for sure, but most grammar gurus say it is perfectly acceptable. The rule is actually a convention. Our understanding has not been compromised, even though we seem to have broken the rule.

The singular they was in common use from the fourteenth century up until Latin scholars in the eighteenth and nineteenth centuries tried to stamp it out. In spite of them, it has never quite disappeared, at least in spoken English. If it makes you feel any better, remember that we use you for both singular and plural, having abandoned the older singular thou. Think of they and them as the polite, ungendered third person singular to use instead of he and she. Even the Shorter Oxford English Dictionary allows it.

Other authors who have used the singular they with someone include William Shakespeare, Anthony Trollope, Robert Louis Stevenson, Walt Whitman, W.H. Auden and even George Orwell (who was a stickler for correct language). For those of you who are not convinced, there are many websites you can check. I have used www.crossmyt.com/hc/linghebr/austheir.html#X1a.

The verb to be
Here is a so-called rule which is really more of a convention. We have all, I’m sure, been taught that there are special rules for the verb to be. A regular sentence has a subject and a verb, usually followed by an object. The girl saw him. He likes her. We will see them. In these sentences, the girl, he and we are all the subjects or actors, and him, her and them are all the objects—something is done to them. But grammarians claim the verb to be is different and we are supposed to use another subject after it. So, we would write It is I or It was he. Not It is me or It was him. This is another rule taken from Latin. Mostly it has disappeared in spoken English and we say It is me. Saying It is I sounds rather pompous.

The rule clings on in written English at times, though. If you want to impress or appease knowledgeable readers, you may choose to use the It is I rule. It is losing ground, however, and many people no longer see it as necessary.

What has happened, sadly, is that people remember there is some kind of rule but can’t quite remember what it is, so they over-correct. It is very common to hear people say She gave the books to Ian and I. (We also undercorrect in the other direction, as in Me and Jenny went to the zoo.)