There is a very interesting discussion about this on Language Log if you’d care to look it up, you may find some articles that will change your mind on the “laziness and ignorance” aspect of SNR “their” usage.

As a linguist, I can tell you that language is indeed fluid and does evolve, and for the past 20 years most linguists have been both happily using “their”, and defending its usage as a single noun referent.

As an undergrad I struggled for a long time with the idea that long-held grammatical “truths” could be toppled by the organic nature of the evolution of language – now I enjoy observing the evolution in progress on the web and elsewhere (in some places it seems more like a devolution, but that’s a digression).

As to your example on public speaking – surely, from a point of view of pure parsing the use of “his” is equally confusing – especially since it could refer to a woman? I’m being deliberately nit-picky here, as I think your argument is somewhat specious – who is the [they], perhaps, but equally, who is the [he]? Bad speech-writing would be at fault more than iffy grammar if there was confusion.

“Everyone” means every person without exception – it is one of those words that makes a person synonymous with a group – removing the individuality of the individual. “Everyone” and all its synonyms refer to the group. A group is a singular entity in grammar.

Literature is the base source of evidence for grammatical rules, spellings, word-meanings etc. Hence the field of linguistic study called philology where the definitions and usages in your dictionary come from. Writing off examples from literature is akin to dismissing the OED because you don’t like where they get their evidence from.

Also: reiterate? Check usage (even linguists have bugbears).

To me, there’s a rather large difference in language changing out of necessity versus out of ignorance. Necessity would include the creation of words such as Internet or computer, words that did not exist for hundreds of years but developed to help the ease of communication. The so-called “singular their” is not comparable to these changes, because there are sufficient alternatives available–people just do not understand how to use them correctly (or possibly are too lazy to take the time). Others have already outlined the alternatives (the use of “him or her,” or the fairly easy rewording of the sentence).

An example I see akin to the improper use of “their” is the improper use of “ain’t.” Ain’t, many moons ago, began as a correct contraction of “am not.” Its misuse has spread, but it has never gained status as correct in the English language. Because of the alternatives, there is no need to adopt “ain’t” as correct, no matter how many people use it on a daily basis. It can be argued that the use of ain’t as opposed to one of the proper contractions is not unwieldy as is the case between the use of his or her in place of their, and therefore it is less necessary than the so-called singular their. However, the sinngular use of their poses other problems, such as the ambiguity other commenters have already outlined. It is not a true solution to the singular pronoun problem.

As far as I’m concerned, there’s a huge difference between formal and informal language, and I firmly believe that the use of their as a singular pronoun should remain in the realms of the informal. While it may not matter in everyday life whether one uses their as a singular pronoun, uses ain’t as a contraction instead of the proper one, or even says “gonna” instead of “going to,” for goodness sake, in formal writing the use of the their as a singular is bound to cause problems: there is no chance to specify what is meant by “their.” If someone were to ask me which “they” I was referring to in the real world, I could simply answer him or her; in writing (or public speaking in which there is no interaction between the audience and the speaker) it isn’t the case. The reader or listener can be left confused, making language ineffective as a means of communication.

The issue with everyone, everybody, and their ilk is that they are simply not referring to a group of people–they are referring to the individuals within the group of people, hence why they are considered singular. Also, no one (as with none) cannot be plural because it is nothing–there cannot be a plural amount of nothing. However, this issue is much harder to understand than the basic pronoun usage, so I find it ever so slightly more acceptable than the aforementioned. Again, it had a lot to do with formality versus informality–I would expect it to be correct in a research paper but not in an e-mail between friends.

To reiterate slightly, I do not think the use of the “singular their” is as much of a necessity as a product of laziness and ignorance about the way the English language works. It does not matter to me that it has been used throughout history–literature is not the standard for correct grammar. With the absence of automated grammar checking programs and easy access to anything and everything relating to grammar (which can be found on the Internet), writing in the olden days was more likely to be incorrect than it is now.

I think that, now that I’ve officially written more than the OP, I can shut up now, and you all have probably gotten the point (if you got through it at all, that is). Have a nice day (or night, depending on who reads this when), and I hope everyone has luck in their future endeavors (pun very much intended).

I find it acceptable in a context where the referent is non-specific, such as almost all of the literary quotations above. “Everyone” and “no one” could be considered to refer to more than one person. That’s like the British use of plural verb and pronoun forms for collective nouns. “Did everyone bring their lunch?” makes sense.

However, “Somebody gave me directions, but they didn’t tell me where to go” is baffling. The sentence means that one particular individual gave you directions, but some other people didn’t tell you where to go. The relationship between the first person and the latter people is unknown.

Presumably, once a given individual has spoken to you, or you have observed that individual doing something, you are aware of that individual’s gender, and may safely use the appropriate pronoun. Even if you’re not sure (perhaps it was an e-mail from a person with an androgynous name), in very few cases would it make any difference whatsoever if you guessed wrongly.

Cases like “someone left their book” could go either way, I suppose, and in casual conversation it would go unnoticed. But, if writing that sentence, I would simply make it “someone left a book.” And examples like “every writer has their style” are ridiculously easy to convert to correct grammar without adding unnecessary complexity. All writers have their own style, and this writer does not use the word “they” to refer to an individual.