"Someone has forgotten their book". Why can we use 'Their" and what's the difference if instead of "their" we use "his/her"?

  • 3
    The biggest difference is that his/her is clunky, while their is natural.
    – user230
    Sep 2, 2014 at 19:09

2 Answers 2


We use they and its derivative forms in this case because we don't know the person's sex. Since English doesn't have a gender neutral singular pronoun, "they" has actually become one:

Singular they is the use of they, or its inflected or derivative forms, such as them, their or themselves, to refer to a single person or an antecedent that is grammatically singular. It typically occurs with an antecedent of indeterminate gender, as in sentences such as:

  • "Everyone returned to their seats."
  • "Somebody left their umbrella in the office. Would they please collect it."
  • "If a person doesn't want to go on living, they are often very difficult to help."

(From Wikipedia)

He is used when referring to a male, and she to a woman, so we can't use them when we don't know the person's gender, such as when we say "someone."

It's actually a complex issue; a lot of people consider the Singular They as informal. I personally think that this is the best option that exists in English. You should avoid it in formal writing by trying to think of another way to say the sentence without "they" (rewriting), because of the people who may think it's ungrammatical (e.g. "Someone has forgotten this book" has the same meaning.) But if you must use a gender-neutral pronoun—don't fight with it and use "they."

Since the issue is complex and everyone has a different opinion, you can use he in formal writing and be backed by linguists who share the same opinion, but it'd sound awkward when using it informally.

A nice article about the subject can be found in here, in case you'd like to see more information.

  • Thank you for that article link. I think it addresses the lack of a gender neutral singular pronoun in a very reasonable way. I think that "they" will become an acceptable substitute for the formal "he or she". The English language has adopted weirder practices in the past.
    – ColleenV
    Sep 2, 2014 at 20:41
  • Can you clarify this part of the answer? "I personally think that this is the best option that exists in English. You should avoid it, but if you must use it then don't fight with it." It sounds like you're recommending it, then recommending not using it, and then something else (but what?).
    – user230
    Sep 2, 2014 at 20:49
  • If you are writing formally, try to avoid using the "singular they." (Rephrase sentences to either use "they" as a plural, or other tricks.) If you are speaking or writing informally, "plural they" is fine.
    – A.Beth
    Feb 8, 2015 at 23:37
  • There are sufficient examples in formal British English of the use of singular they and indeed in books on English usage (eg Fowler) that I would not criticise anyone for using it. If one of my students used "he" for an unknown person in an advice letter I would correct it to "they" and I would never use "he" for an unknown person in contract drafting or writing that is more formal than that. Mar 24, 2015 at 20:42

In situations where we don't know the gender of the subject they is often used as a way of saying "his or her" or "he or she" even though it's incorrect because there is only 1 subject. In these situations a singular subject must be picked, or something like "his or her" can be used. Historically he was commonly considered the default singular go-to, but the speaker can choose her instead if he likes (See what I did there?). For example:

Someone forgot his bag.

The use of their should be used for plural unknowns only. For example:

Everyone forgot their bags.

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