There are many grammar rules that the student of English must learn about in order to understand how the language works. There are some rules, however, that don’t reflect how the language works at all and are simply passed down from generation to generation just because. It’s good to be familiar with them for the same reason it’s good to know arbitrary dress code customs, which is to say, because someone might judge you for not following them, but they have little to do with logic, clarity, the facts of English, or even being a good writer. Here are four grammar rules that aren’t really rules at all.
1. DON’T SPLIT INFINITIVES.
The rule against splitting infinitives says that nothing must come between a to and its verb. It is incorrect to boldly go. One must instead arrange to go boldly, or boldly to go. But this rule has no real justification. In fact, this rule was never mentioned in any treatises on English until an 1834 anonymous article proposed it, claiming that keeping the to and the verb next to each other is what good authors did. But plenty of good authors had in fact been splitting infinitives for hundreds of years, from John Wycliffe in the 14th century to Samuel Johnson in the 18th.
Though many writers thought this imaginary rule was unnecessary and even sometimes harmful to clarity (George Bernard Shaw said, “Every good literary craftsman splits his infinitives when the sense demands it”), it somehow made its way into a number of usage guides and stayed there. Read Tom Freeman's history of the rule here.
2. DON’T END A SENTENCE WITH A PREPOSITION.
We are told not to end a sentence with a preposition. What is this rule for? I mean, for what is this rule? Wait, would anyone really use the second construction to ask this question? Ending a sentence with a preposition is completely natural in English and not at all wrong. The rule came about during the 17th century when scholars were deeply immersed in the study of Latin and took to emulating Latin as a model of linguistic purity. Because a preposition can’t be stranded in Latin, some thought that the same should hold for English. But English differs from Latin in countless ways, and to cling to a prohibition that forces you to swap It’s nothing to worry about for It’s nothing about which to worry does not encourage good style or clarity of expression. Don’t believe me? Ask Oxford Dictionaries.
But what about sentences like Where’s he at? or Do you want to come with? Should those be considered correct, then? No. Those are examples of non-standard grammar because they're used in non-standard dialects, not because they end with prepositions. At where is he? does not sound any better, and if the problem with come with is the ending preposition, why doesn’t come along sound just as bad?
3. DON’T USE "THEY" AS A SINGULAR PRONOUN.
The rule says that because they is a plural pronoun, it must have a plural antecedent. This means that the sentence If anyone has a problem with that, they should tell me is wrong because anyone is singular and they is plural. They should be switched to a singular pronoun, but which one? “Generic he” was the prescription in the 19th century (If anyone has a problem with that, he should tell me), but as it became clear that he was neither generic nor neutral, the suggestion was to either use the cumbersome “he or she” (If anyone has a problem with that, he or she should tell me) or to rewrite the sentence entirely (Got a problem with that? Let me know).
Sticklers have been wringing their hands about how to reconcile this rule with guidelines for nonsexist language for decades now, but the solution has been right there all along. Just use singular they. The pronouns they/them/their have been used with singular antecedents for centuries. It’s perfectly good English. It sounds completely natural. Great writers like Shakespeare and Austen used it. Does anyone really think Everyone clapped his hands sounds better than Everyone clapped their hands?
Editors like John McIntyre of the Baltimore Sun have been letting the singular they through for a while now and most of the time no one notices. What we have in singular they, according to linguist Geoff Pullum, is “a logically impeccable construction that expert users of the language regularly employ and experienced listeners unhesitatingly accept. I wonder what more one would need to take something to be grammatical.”
4. DON’T START A SENTENCE WITH "HOPEFULLY."
The ban on hopefully as a sentence adverb meant that you were only to use it to mean “in a hopeful manner.” So I waited hopefully was good, but Hopefully, the bus will get here soon was bad. Buses don’t do things in a hopeful manner! What you were supposed to say in that situation was It is hoped that the bus will get here soon.
Hopefully was being picked on rather unfairly. No one had a problem with fortunately/clearly/unbelievably/sadly/mercifully the bus will get here soon. There are plenty of other adverbs that can modify a whole sentence without causing a stir. Hopefully was singled out because it was new in the 60s, people noticed it, complained about it, and made up a reason to justify their complaints. It is still one of those gotcha words that attract the red pen, but even the AP Stylebook has given up trying to enforce the ban.