While educated people agree on most grammatical rules, there are fierce debates on a few key points. We're going to lay down the most controversial rules and explain when to follow them and when to break free.
Can you split infinitives?
People have tried to argue for centuries that the two words of an English infinitive (e.g., "to be") should not be interrupted by another word (e.g., "to not be"). This preference derives in part from infinitives appearing as single, indivisible words in most languages, including Latin, which English scholars have long idolized.
Although there is no clear justification for this rule, you should still follow it most of the time. After all, many think that it sounds better not to split infinitives. More importantly, split infinitives may annoy readers who believe in the rule, and that's generally something you should avoid.
There are times, however, that call for a deliberate exception. You may split infinitives when it helps for clarity, as in, "We expect our output to more than double." You may also split infinitives as a rhetorical flourish — knowing that you risk offending people — as in the Star Trek mantra, "To boldy go where no one has gone before."
(Note that newer versions of Star Trek amended the original slogan, "To boldly go where no man has gone before," for the sake of gender equality but did not touch the split infinitive.)
Can you end a sentence in a preposition?
The prescription against stranded prepositions may also derive from an idolization of Latin. It has been passed down by pedants since first enunciated by John Dryden in 1672 in criticism of Ben Jonson's 1611 phrase "the bodies that those souls were frighted from."
But the truth is, there is no good reason for this rule and adhering to it will often make you sound stupid. An unknown British government worker (not Winston Churchill) demonstrated its ridiculousness in his retort to a copy editor who tried to apply the rule: It is an "offensive impertinence, up with which I will not put."
In fact, it is often natural to end sentences in prepositions, such as in passive structures, relative clauses, infinitive structures, and questions beginning with who, where, what, etc.
Just be careful not to end a sentence in an unnecessary preposition. It looks bad to write, "Where are you going to?" or "Where are you at?" when "Where are you going?" and "Where are you?" will suffice.
Can you use the generic "you"? (We just did.)
Back in the day, English speakers used "one" to refer to an unspecified person. Then again, they also used pronouns like "thou" and "thee."
In modern times, most people agree that "one" sounds pompous and old-fashioned, and they prefer to use "you" in its place. For instance, "You can't always get what you want."
Although the generic "you" used to be nonstandard, it is acceptable today in all but the most formal contexts.
Should you use the generic masculine?
It once was standard to use "he" to refer to a person of unspecified gender. The word was supposed to encompass female antecedents in the same way that "man" or "mankind" could refer to women as well.
Around the 19th century, however, people began to recognize the sexist implications of this rule. Why is the male form the default? What sort of message does it send to women when every person of unspecified gender is referred to as "he"? For instance, the sentence, "A good trader follows his instincts," may suggest that most traders are, or ought to be, male.
Unfortunately, there is no simple solution to this problem. "He or she" is wordy and "they" violates another rule by using a plural pronoun to refer to a single person. Always using "she," or arbitrarily or non-arbitrarily switching between "he" and "she," is also problematic or confusing. And there are still those who defend the generic masculine.
What's a good, progressive writer to do? In many cases you can dodge the problem (e.g., "Good traders follow their instincts"). Otherwise you will have to pick your poison.
Can you start sentences with conjunctions?
As often as you hear that you should not start sentences with "and," "but," or other conjunctions, this rule has "no historical or grammatical foundation," according to the Chicago Manual of Style. Indeed, "perfectly respectable writers employ this disputed usage, and have done [so] since Anglo-Saxon times," writes Oxford Words Blog.
Reasons for starting a sentence with a conjunction may include simplifying a long and complex sentence or emphasizing the conjunction itself.
Although you can break this rule, try not to get carried away. Needlessly starting sentences with conjunctions will only annoy people.
Can you use "like" as a conjunction?
"Like I was saying," may sound fine to most people, but it is abhorrent to grammar snobs, who say you should swap "like" for a proper coordinating conjunction like "as."
"Setting aside the adolescent propensity for like as a syntactical oral hiccup, there is no more grating solecism than this word's use as a conjunction," writes book critic Michael Dirda.
The use of "like" in place of a subordinating conjunction (a word that connects two clauses) has been recorded as early as the 15th century. Nonetheless, "it is still frowned upon and considered unacceptable in formal English," according to the New Oxford American Dictionary.
In proper English, "like" is used most commonly as a preposition, as in "fly like a bird," and sometimes as a noun or adjective.
Do you have to say "whom"?
You should generally use "whom," the objective case of "who," in formal writing.
In most contexts, however, even grammar nuts agree that it often sounds pretentious to use "whom" and "whomever." That's why the use of "who" or "whoever" in these contexts is "broadly accepted in Standard English," according to the New Oxford American Dictionary. Follow your instincts on which form of the interrogative or relative pronoun to use.
Can you use object pronouns after "than" and "as" — or after linking verbs?
Should you write, "She is taller than I," or, "She is taller than me"?
Traditionalists argue that "than" and "as" are conjunctions and should therefore be followed by subject pronouns (e.g., "I" and "she"), with an attached clause that may or may not be implied (the full form of the previous example would be, "she is taller than I am.")
But many, including Shakespeare on occasion ("A man no mightier than thyself or me ..."), choose to use object pronouns (e.g., "me" and "her") in this situation because they sound more natural. This practice can be defended by claiming that "than" and "as" are serving as prepositions.
At this point, both forms are acceptable, and you should use whichever feels best.
As for "this is she" versus "this is her," both are seen as acceptable things to say on the phone (or elsewhere), according to The Merriam-Webster Dictionary of English Usage. The former is formally correct because many say linking verbs like "is" should be followed by a subject pronoun. The latter is acceptable because many think it sounds more natural to use an object pronoun, and the supposed rule about linking verbs taking subject pronouns may be just another overzealous application of Latin.
What is the real difference between "less" and "fewer"?
The rule that you always hear is to use "less" with uncountable things and "fewer" with countable things. For example, "I drank less beer and smoked fewer cigarettes."
In fact, the rule is bogus — but you should follow it anyway.
It is bogus because "less" has always been used with countable things, with Alfred the Great writing around 880, "Swa mid læs worda swa mid ma ... " meaning, "With less words or with more ..." Indeed, the rule about counting apparently derives from the arbitrary preference of a grammarian in 1770.
You should follow it anyway, however, because pretty much every educated person does, and you don't want to look like an idiot.