A common issue found in a lot of writing is the tendency to see “they” used as a pronoun for a singular object. It’s hard to write without that being the case, actually, because it sounds right. Here’s an example:
If a person wants to earn a lot of money, they will have to work very hard.
The grammatical error in that sentence is that “they” is referring to “a person”, but “they” is a plural pronoun while “a person” is singular. Yet I think it sounds right. Said aloud in a conversation, few people would think twice after hearing that phrase. This begs the question, though: if the sentence above is gramatically incorrect, how should it be reworded to mean the same thing? One possibility is to use “he or she”, as in:
If a person wants to make a lot of money, he or she will have to work very hard.
The problem with that is it’s wordy, and using just “he” or just “she” could come across as anachronistic, or even sexist. Another alternative is to turn the object of the sentence into its plural form, but that doesn’t always work. For example:
It people want to make a lot of money, they will have to work very hard.
That is correct, I believe, but it doesn’t mean the same thing as the original statement did. Sometimes it works well enough, as in:
If a student wants to succeed, they will have to study often.
Versus:
If students want to succeed, they will have to study often.
If precise grammatical correctness isn’t a big deal, though, then in most cases the best option is to just use “they” as a singular pronoun. It’s accepted in speech in all but the most prudish of environments. It’s probably only a matter of time before it becomes acceptable grammatically too.
Linguistics will tell you that the writing and correct forms of a language always trail behind the actual usage of a language. Put in other terms, the popular forms of words tend to become the correct form of words, given enough time and enough usage. Although that doesn’t always happen. Look at Latin: historians believe the spoken (or “vulgar”) form of Latin was miles apart from the more erudite written form in the A.D. era. Then again, literacy was much less common in those days too!
The source for most of this post is: http://oxforddictionaries.com/words/he-or-she-versus-they
