Mad Scientist,
The distinction between prescriptive and descriptive is interesting, it highlights how a living language’s rules change in speech before they’re changed in textbooks. English is not a particularly perscriptive language anyway, compared to other languages where elementary school students get indoctrinated with intricate grammar rules. English grammar, on the other hand, is assimilated subconsciously, while rules are only used to point out exceptions, and often take the form of funny mnemonics such as “I before E, except after C, and when it sounds like AYE as in weight, and a few more stragglers such as WEIRD and foreign words such as EISENHOWER”.
So English is not a language of strict rules, it’s more like open-source software, we’re free to modify and add to it. So which rules can we ignore and which should we enforce? It’s a tough call.
I’ve an Indian collegue, who speaks the English he grew up with. He says things like “marks-it” to mean his college transcript, and “hill station” to refer to a resort in the mountains. These are perfectly valid regional variations. But he also tends to say “very less” instead of “very few”. When he does, I feel the need to correct him. Should I? After all, his intended meaning is clear.
A good example of descriptive grammar is double negatives. “I didn’t say nothing” is perfectly clear when used in speech, assuming the right emphasis is put on “nothing”. However it’s prescribed as wrong in English grammar. The fact that double negatives are the norm in many languages such as Spanish, French, Russian… shows that there’s no fundamental flaw in them. The weakes argument is that double negatives cancel one another out… if this were so, then a triple negative would be perfectly acceptable.
Another example is the “S apostrophe S” issue. The rules state that “United States’s”, “Jones’s” is the right form, but many people will simply drop the last S, either in writing or only in speech.
I think the deciding factor should be, does bending the rules for convenience clarify or cloud up the meaning. By this measure, double negatives are OK, dropping the last S is not. I tend to think that singular “they” falls into the latter, since it leads the listener to think that the subject may be plural. But again, with the right spoken emphasis, confusion can be avoided. So perhaps we can conclude that such rule-bending is acceptable in speech, but not in writing.