Tag Archives: proofreading

Common Grammar Mistakes: Let’s versus Lets.

Common Grammar Mistakes: Let's versus Lets. (From jdeeringdavis on Flickr.)

This week, while working with a number of students on their final papers and transfer essays, a particular grammar question popped up. Well, to say it “popped up” is a bit of an understatement; this question came from not one, but SIX students, separately, yet almost all on the same day. (Travis, you broke up the would-be flash mob. Shame on you.)

So, because my students have assumed a Voltron-like formation to ask me the same, exact question (!), I will answer it here.

What is the difference between let’s and lets?

“To let” means to allow or to permit, as in “I let the dogs out each morning.” It also means to lease or rent, as in “Wanted: Apartment to let” but let’s (HA!) not get ahead of ourselves here.

“Lets,” then, is the third person singular present tense form of “to let.” Translation: you use it with he, she, or it when using the present tense, like this: “Sally lets her brother use her bicycle on weekends.”

Easy enough, right? Now, for the second part.

“Let’s,” with an apostrophe, is a contraction of “let” and “us.” It is commonly used in first personal plural commands, like “Let’s go!” or “Let’s eat!” For the less enthusiastic, “let’s” commands without exclamation points suffice as well.

As a contraction, “Let’s go!” really means “Let us go.” This contraction, like most others, is more informal– after all, trips to the grocery store don’t have to be quite so dramatic.

Here’s another example of what I mean: “Guys, let’s go to the beach.” In reality, you’re really saying “Guys, let us go to the beach,” albeit in a less formal, contracted way.

So, therein lies the difference: “Lets” is a third person singular conjugation of the word “let,” as in, “She lets me watch sports” or “It lets you download more information.” “Let’s,” in turn, is the contraction of “let” and “us,” used in plural commands, such as “Let’s get started” or “Let’s get married.”

A good rule of thumb:
To ensure you’re using the proper form of “let’s,” substitute “let’s” with “allow us” when constructing a command. It’s an extra step but, by keeping this in mind, you’ll be sure to choose to right form.

Here’s what I mean:

With “let’s”: Let’s grab some sushi.
With “allow us”: Allow us [to] grab some sushi.

This makes sense, right? It may be overly formal, but it’s nonetheless grammatically sound. Of course, you don’t actually have to substitute “let’s” with “allow us” in your writing; however, by keeping this in mind, you will know (and use!) the correct choice.

And, that’s it. Once you know the difference, it’s easy to remember. Granted, I don’t have a funny mnemonic this time around (sorry!), but it’s relatively easy to keep these two straight.

Common Grammar Mistakes: Which versus That.

Which versus That. (From-Paul V8 on Flickr.)

Knowing the difference between which and that can be a bit confusing. Which one do you use? That one? Okay, I’ll stop.

What makes matters worse is that there has been a shift in usage and definition over the last century. While you may not be using grammar books from 100 years ago, you’re more likely to encounter this change in literature as so many classics are over a century old.

So, which one do you use, and how can you tell the difference?

Ultimately, it boils down to the difference between two types of clauses.– restrictive and non-restrictive. A restrictive clause is one that limits or restricts the scope of the noun it is referring to. A non-restrictive clause, as I’m sure you can imagine, doesn’t. Here is what I mean:

The cheese that is stinky is delicious.
The cheese, which is stinky, is delicious.

In the first example, the clause “that is stinky” is a restrictive clause, because it limits the scope of the word “cheese”, as it is only referring to the cheese that is stinky. It isn’t referring to any other cheese except that one. If you remove the clause, you are only left with: “The cheese is delicious.” Without the clause, the reader no longer knows which cheese is being referred to and the sentence loses crucial information– not just any cheese is delicious.

In the second example, the clause is non-restrictive: the cheese’s stinkiness is additional information about a cheese being described. Basically, the clause which is stinky is here parenthetical —as in, “by the way, the cheese happens to be stinky.” It is an additional piece of information but it’s not essential to the sentence’s meaning.

Here’s another example:

Another great type of cheese is one that is blue-veined and harder than most.

The clause “that is blue-veined and harder than most” modifies and constrains “one”. Another great type of cheese is not just any other cheese but one particular type. The clause is restrictive,especially considering how little sense the sentence would make without it.

In terms of punctuation, there are two hard-fast rules to follow:

  • Restrictive clauses are not separated from the rest of the sentence by commas.
  • Non-restrictive clauses must be separated by commas from the rest of the sentence to indicate parenthesis.

This all seems fairly simple, yes?

Of course, I can’t end this blog post without listing a few exceptions to complicate things a bit. I don’t know about you, but I can certainly think of a few examples that defy the rules I’ve listed above, yet still make perfect sense. In fact, few writers have ever followed these rules systematically, and it’s easy to find examples where either relative pronoun is used with restrictive clauses. Here’s an example:

A vase which has lost its bottom is useless.

The clause which has lost its bottom is certainly restrictive; without it, you’re left with “A vase is useless” which you can agree makes no sense. Now, according to the traditional rules, which should instead be that. However, did you have any trouble discerning the sentence’s meaning? I’m guessing the answer is no.

It also comes down to a question of style. Granted, style is a bit harder to pin down as “it just sounds better” is hard to define as preferences to consonant stress and rhythm. (For the linguist geeks in the house, that provides a softer, relatively unstressed sound while which is harder and easier to stress.) . But, in certain instances, it does “just sound better” to use that instead of which. Here are a few examples; again, they don’t necessarily abide by the rules, but they are definitely points to keep in mind.

  • In clauses that follow impersonal constructions, such as it is, that is preferred: “It was the plant that fell”.
  • Clauses that refer  to the words anything, nothing, something, or everything have a slight preference for that over which: “Can you think of anything that still has to be done?”
  • Clauses that follow a superlative also tend to prefer that: “Thank you for the best night that I’ve ever had”.

By throwing these wrenches in, I’m not suggesting to completely ignore what I just said. After all, if that were the case, I would just delete this blog post entirely. What I am suggesting, however, is that language is fluid– yes, there are rules, but sometimes you can bend them a little– and you CAN use which instead of that sometimes, so long as your meaning is well-understood.

That being said, it doesn’t apply the other way around; non-restrictive clauses should always to start with which. That’s just the way it is. Likewise, the punctuation rules will always apply– non-restrictive clauses always need commas, but restrictive ones (whether you use that or which) don’t. Without the proper punctuation, your whole sentence can go awry and your meaning could get totally lost. So, if you do decide to bend the rules, you have to do so carefully. If you’re not sure (and it’s understandable if you’re not), then just follow the restrictive/non-restrictive rules I’ve first outlined above and you’ll be fine.



Grammar Myths Debunked: Ending a sentence with a preposition.

Ending a sentence with a preposition. (From Remixer 96 on Flickr.)

In my last grammar post, I covered how starting sentences with because is actually grammatically acceptable. Now, I will show you how you can also end sentences with prepositions, contrary to what grammarians and English teachers may tell you.

Students are taught time and again that you cannot end a sentence with a preposition; I certainly remember learning this in grade school. This lesson is also attributed (wrongfully, I’m afraid) to Winston Churchill as well.

The origin of this myth stems from a 17th century notion that English was inferior to Latin and that, in order to approve upon it, English should abide by Latin’s grammar rules. (If you’re nerdy like me, you can read more about that here.) But, as English is an ancestral German dialect, these Latin rules does not fit the natural structure of English comfortably.

So, what does this all mean?

Well, first off, there are certain sentences that almost can’t be formed without ending with a preposition without sounding ridiculous.

In the famous story woefully misattributed to Winston Churchill, he complained “…[t]hat is the sort of thing up with which I will not put!” when criticized by a newspaper editor for, well, ending a sentence with a preposition. Wrong story or not, this nonetheless highlights how sentences can sound nonsensical when following this “rule.”

Here are some more examples:

The ring had not even been picked out. This sentence sounds good and ends in a preposition. It is also grammatically correct. See?

Picked out the ring had not even been. This sentence, while grammatically correct, resembles a quote from Yoda. This clearly doesn’t work as well.

The marathon was rained out. While this isn’t such good news for the runners, it is a perfectly good sentence that –you guessed it– ends in a preposition.

Rained out was the marathon. This is yet another Yoda impression that doesn’t work.

So, why is this the case?

Often, what looks like a preposition in an English sentence is actually not a preposition at all. Instead, it is a part of the verb, to create a phrasal verb. These words are prepositions on their own but, when combined with certain verbs, become adverbial particles and part of these phrasal verbs.

Examples of these phrasal verbs are:

  • Branched out
  • Throw up
  • Put up
  • Shut up
  • Got off

As such, it is preferable to say “Where do you get off?” rather than “Off where do you get?” And, it is perfectly fine to say “Let’s kiss and make up.”

But, yes,  there are circumstances where you shouldn’t to end your sentence with a proposition. If the meaning of your sentence does not change with or without the preposition, then you should not include it. So, “where are you at?” is still incorrect, as it means exactly the same as “where are you?” (Sorry.)

Of course, this is a much contested rule so, if you’re still not sure, here’s further proof:

The spurious rule about not ending sentences with prepositions is a remnant of Latin grammar, in which a preposition was the one word that a writer could not end a sentence with. But Latin grammar should never straightjacket English grammar. If the superstition is a “rule” at all, it is a rule of rhetoric and not of grammar, the idea being to end sentences with strong words that drive a point home. That principle is sound, of course, but not to the extent of meriting lockstep adherence or flouting established idiom.

(Garner’s Modern American Usage, Oxford University Press, 2003)

Grammar Myths Debunked: Starting a sentence with “because.”

Grammar Myths Debunked: Starting Sentences with "Because" (From dickdotcom on Flickr.)

A frequent issue that comes up while editing is whether or not sentences can start with the word, “because.” This answer to this question is actually hotly contested… and often misconstrued.

Can you start a sentence with “because”?

The answer is yes. Yes, you can! It’s perfectly okay to start a sentence with because. The word, because is a subordinating conjunction; meaning, it introduces subordinating clauses. In function, it is similar to the words after and although, and the phrases as if, and in order that— all words that can begin sentences without a problem. See?

However, you still have to be careful– when using because or any  other subordinating conjunction, you must have a main clause in your sentence. Meaning, you cannot use a subordinate clause on its own, as it would be a fragment.

Here is an example of what I mean.

Because I woke up late, I missed my flight.

This sentence is correct. Why? “I missed my flight” is the main clause of the sentence– meaning, this clause, by itself, is a perfectly fine sentence that can stand up on its own. A subordinate clause can augment a main clause but, as it is subordinating, it cannot stand by itself. “Because I woke up late” by itself would be a fragment.

A helpful way to remember this is to think of subordinating clauses separately, and consider whether it provides enough information in its own to satisfy what needs to be known. Such as:

Because the table was wobbly, I spilled some of my coffee.

“Because the table was wobbly” doesn’t offer enough information on its own: because the table was wobbly what? What happened? Why does the table’s wobbliness matter? “I spilled some of my coffee” is the answer to these burning questions.

In these examples, I’ve formed these sentences to be [subordinate clause] + [main clause]  so the difference is immediately clear– they are separated by a comma and are easier to spot. However, the same rules apply if you are to write these sentences as [main clause] + [subordinate clause]. Such as:

I missed my flight because I woke up late.

“I missed my flight” stands on its own and, while it’s a crappy situation, gives enough information by itself. “Because I woke up late” still doesn’t make sense, without being prefaced with what happened, first.

I spilled my coffee because the table was wobbly.

Likewise, “I spilled my coffee” is another unfortunate situation that can stand alone. “Because the table was wobbly” is not enough to stand up by itself.*


*I promise this pun was accidental!



Common Grammar Mistakes: Fewer versus Less

Common Grammar Mistakes: Fewer versus Less. (By Jennifer Peyton from Flickr.)

So, for today’s grammar topic, I’m covering the difference between fewer and less.

Now, less and fewer pretty much mean the same thing—they both mean the opposite of more. So, what’s the problem?

Well, what differentiates these two is not their definition, but the types of nouns that they are used to describe. At its most basic, the rule is that you use less with mass nouns and fewer with count nouns.

Count nouns are, well, things that you can count. Whether they are books, pens, or Skittles, these are all things that can be counted individually. So, if you can count them, it’s a count noun which means it belongs with fewer, as in, “You should eat fewer Skittles.”

Mass noun, on the other hand, are nouns that describe things that can’t be counted individually. These can’t be pluralized– for example, rice, dust, or wool are all mass nouns, all words that can’t be made plural. Because these things can’t be counted individually, so they are described with the word less. For example: “If I had less dust in my house, I wouldn’t sneeze as much.” This clearly makes much more sense than “If I had fewer dusts in my house.” So, if you have difficulty pluralizing the word — the words clutter, leather, and cloth are more examples– then this signifies that it is a mass noun.

Sometimes, however, determining certain words as being either count nouns or mass nouns can be a bit confusing. For example, coffee or soda can be either count nouns or mass nouns depending on how they are referred to. For instance, if you are making coffee, it is a liquid that can’t be quantified– so, if the coffee pot overflows, you need to make less coffee next time. Yet, if you’re a barista making cups of coffee as a barista, you may need to serve fewer coffees if patrons decide to leave. Of course, the noun that is actually being count is the word cups — the cups are being counted, not the coffee itself– but, it is common to refer to a cup of coffee as just “a coffee” and so this distinction must be clear. Mass nouns (like coffee) can’t be made plural but, in this case, it can be made into a count nounI’ve made a mass noun plural, but in the process I transformed it into a count noun.

Another tricky noun is the word furniture; it isn’t immediately obvious whether it is a mass noun or a count noun. Like coffee, it is technically a mass noun, even though it can describe multiples of count nouns– there can be countable pieces of furniture, but furniture itself is a collective name for a mass of stuff. You could say, “There are too many places to sit; we need fewer couches,” but you would never say, “we need fewer furnitures.”

Of course, we can never be without exceptions. For instance, it is customary to use the word less to describe time, money, and distance. Yes, they are quantifiable, but they require less rather than fewer: “The flight time is less than two hours so I hope to pay less than $350 per ticket.” But, aside from time, money, and distance, the rules I stated above remain the same.

So, now that we’ve gotten count nouns and mass nouns straightened out, let’s finish up by clarifying a very important fact: Most signs for supermarket express lanes are wrong. As you know, most of the signs for these lanes read, “10 items or less.” Now you know that these are grammatically incorrect and should instead read, “10 items or fewer.” Why? Because, of course, items are individual, countable things. As such, they are count nouns which means it uses the word fewer. Why this mistake is made in practically every grocery store and supermarket is beyond me but, at the very least, now you know the difference.


Purple prose: What it is and how to avoid it.

Purple prose is the name given to writing — or, well, prose– that’s just too flowery and too melodramatic for its own good. In other words, just way too much.

“Why would purple prose be a bad thing?”

Well, it clouds the meaning behind your writing and, frankly, doesn’t flatter the writer very well. By its sheer verbosity, purple prose can turn off your reader greatly– which is not a good thing to do if your reader happens to be your professor.

That being said, there actually is no ultimate, absolute definition of what constitutes prose, nor is there a definite list of symptoms. Figuring out whether you have in fact fallen victim to purple prose is often a subjective decision– one person’s purple prose may be another person’s vivid description. Unfortunately (or, fortunately, depending on who you are), this is largely a judgment call.

However, that is not to say that there aren’t basic ground rules to follow; this isn’t a free-for-all. (Sorry!)

So, here are a few things to keep in mind in order to avoid purpling your prose too much:

Avoid words that are too big and fancy. Obviously, there is merit to being erudite and eloquent. However, there is a difference between using a particular word because of its precise definition and using it because it makes you sound smarter. Be honest with yourself, your own writing style, and pay attention to the task at hand. It’s easy to spot when a student is using difficult words for the sake of using them– trust me, I know. Everyone has a particular writing style that is rather distinctive– much like someone’s speaking voice. So, when a student puts on airs, it’s much like someone you know well suddenly speaking in Muppet-voice. And it’s that much more obvious when unnecessarily difficult words are used where clear, simple wording would suffice.

Keep the urge to write flowery, overly vivid descriptions at bay. Descriptors are used to make the reader visualize what you’re describing. However, there is such thing as written sensory overload. Not sure what I mean? Well, here is an example:

The Bulwer-Lytton Fiction Contest is an annual contest held by the English Department of San Jose State University. The contest challenges entrants to write the opening lines of the worst possible novels. Of course, each year’s submissions are hilariously bad renditions of “good fiction.” While they are opening lines to non-existent fiction (how is that for a double negative?), they are also excellent exercises in flowery writing, or purple prose.

This is the 2008 grand-prize winner of the Bulwer-Lytton Fiction Contest:

Theirs was a New York love, a checkered taxi ride burning rubber, and like the city, their passion was open 24/7, steam rising from their bodies like slick streets exhaling warm, moist breath through manhole covers stamped “Forged by DeLaney Bros., Piscataway, N. J.”

Um, what?

First off, thanks for making New York sounds gross(er). Second, there are way too many descriptions–far more than what’s necessary. This, in all its flowery craziness, is an example of vivid imagery gone awry– this, my dear readers, is purple prose.

Avoid self-indulgent writing. Another clue to whether the writing is overdone is that it draws attention to itself rather than to the story. If you find yourself thinking, “By golly, that’s a lovely phrase”, then you’re in trouble. If the phrase is self-indulgent and is far more about your own cleverness than it is about your topic itself, then it has to go. This is, according to William Faulkner Sir Arthur Quiller-Couch*, is called “murdering your darlings.” In his series of lectures titled On the Art of Writing  from 1916 (!), Sir Quiller-Couch wrote: “Whenever you feel an impulse to perpetrate a piece of exceptionally fine writing, obey it–wholeheartedly–and delete it before sending your manuscript to press. Murder your darlings.” Nicely done.

Of course, that is not to say that you have to slaughter or even dump every phrase you are particularly pleased with. You are allowed to marvel at your own genius, yes. So, if there is a phrase in mind that borders on possibly too much, think: if the phrase serves your topic well, it stays but, if it doesn’t, buh-bye. It’s that simple.


*William Faulkner is frequently attributed to the phrase “kill your darlings” when, in actuality, it was Sir Quiller-Couch who coined it. The more you know.

Common Grammar Mistakes: A versus An.

A or an?

This question came up earlier this week and, well, here I am to save the day. Most have learned that you use a before words that start with consonants and use an before words that start with vowels. However, it’s actually a bit more complicated than that.

The rule actually is that you use a before words that start with a consonant sound and an before words that start with a vowel sound.

The question at hand was actually regarding the word “hour” and whether an hour is correct as opposed to a hour. To answer this question specifically, an hour is correct, because hour starts with a vowel sound.

Words that begin with h or u are most confusing because these words can start with either vowel sounds or consonant sounds, regardless of whether a consonant or vowel is actually being used. For example, it is a historic moment because historic starts with an h sound (the h in “h-h-hey!”) but he’s an honorable fellow because honorable starts with an o sound. Similarly, it is a Utopian idea (“you”-topian”), but an unfair world (“uh-nfair”).

The letters o and m can be tricky too, for the same reasons. For example, you would use aif you were to say, “She has a one-track mind,” because one-track starts with a w sound. Similarly, “She has an MBA, but chooses to work as a missionary.”

One complication is when words are pronounced differently in British and American English. For example, the word for a certain kind of plant is pronounced “’erb” in American English and “herb” in British English. So the proper form in America is an (h)erb, and the proper form in Britain is a herb. In the rare cases where this is a problem, use the form that will be expected in the vernacular of the country in question.

I know this seems confusing –I’m sure way more confusing than originally thought!– but, remember: it is the sound that governs whether you use a or an, not the actual first letter of the word.

Common Grammar Mistakes: Double negatives.

“Why are double negatives so bad?”

I was asked this question recently by a student, and I decided to answer it here.

Double negatives often amount to much confusion– not because of misconstrued usage like lay and lie or affect and effect, but because of misplaced meaning. Like dangling participles, double negatives create ambiguity within a statement, potentially confusing the reader.

Wait, I still don’t get it; what’s a double negative?

A double negative is where two forms of negation are used in the same sentence. When this happens, the negation in the sentence isn’t intensified or made “double-bad”– it is instead made positive.  In essence, two wrongs do make a right, in the case of double negatives anyway. For those of you who know formal logic, this will sound very familiar to you. There are exceptions, but, unless your writing in a foreign language, they does not apply here: in languages like French or Spanish, the use of double negatives do mean something is super-ultra-mega-bad but, in English, it does not.

Here are a few examples of double negatives:

  • I don’t not love you
  • I can’t get no satisfaction
  • We ain’t got no history
  • We don’t need no education

In these examples, the double negative creates an opposite meaning: the two negatives cancel each other out and form a positive sense.  So, “I don’t not love you” becomes “I don’t not love you,” and “we ain’t got no history” really means “we ain’t got no history.” Aw.

Of course, double negatives can sometimes be used creatively, such as in advertising; when “Nobody doesn’t like Sara Lee” is sung, what’s being implied is that everybody likes Sara Lee. However, even in creative use, double negatives can lead to some confusion: is Pink Floyd really calling for thought control? Is Mick Jagger really asserting his ability to in fact gain satisfaction, as opposed to, well, not getting any?

As such, the double negative is, generally speaking, to be avoided– that is, unless you’re using it within a creative context. Who knows what Roger Waters was going for but, at the very least, be mindful of it yourself.


Common Grammar Mistakes: Affect versus Effect.

Affect and effect are so often confused, they are practically the original common grammar mistake. They are misconstrued nearly every which way, everywhere,  on a nearly daily basis. Of course, all these errors are easily avoidable, and here’s how.

First, you have understand the intrinsic differences between these two words. For the most part, this difference is actually pretty straightforward: one is commonly used as a verb (affect) and one is commonly used as a noun (effect). Easy, right? These two can actually be switched but let’s start with the basics first.

Affect, as a verb, means to influence, as in “My recent lottery win has affected my spending habits greatly” or “His recent knee surgery affected his gait.”

Effect, as a noun, means a result, as in “My recent lottery win had a clear effect on my spending habits” or “His recent knee surgery had an obvious effect on his gait.”

Here’s an easy way to tell them apart:

An Affect is  an Action, but an Effect is an End result.

Awesome, right? Now, let’s move on.

Rare uses of Affect and Effect

So, I hinted above that these two can be used differently than how I had previously explained.  In rare instances, they can, in particular circumstances.

In psychology, affect can be used as a noun– as in, “She displayed a happy affect.” This definition is used in psychology to signify the difference between knowing a person’s mood really is and knowing what their mood appears to be. Meaning, it’s hard to discern whether the person (or, really, patient) is actually happy or just appearing to be happy. In psychology, this difference is important.

Effect, in turn, can be used as a verb, meaning to bring about, cause, or accomplish. For example: “The President hoped this new program would effect change.” Here, effect is used as a noun. Here is another example: “Andy effected his escape from prison with a rock hammer and a carefully placed poster.” Of course, this usage is less common; it is used predominantly in political writing and journalism.

Like most common grammar mistakes, these two words seem confusing but, with a little thought and maybe a memory trick or two, they’re actually very easy to tell apart.

Common Grammar Mistakes: Who and Whom.

Common Grammar Mistakes: Who versus Whom.

Okay, guys. I’m about to embark on one of the most confusing aspects of grammar and word choice. It is mistaken so often, I would have go into spasms if I even attempted to address it at every encounter. Alas, this is a daily struggle. So, with that, I will describe the differences between who and whom, how to use them, and, most importantly, how to avoid mistakes. First, in order to fully understand the differences between these two, we also must discuss the differences between subjects and objects. I have covered this in previous grammar posts but  here is a brief refresher for you. To help remember the differences between subject and object, you can use this interesting mnemonic:

I love you; you are the object of my affection.

Aw, how sweet. This mnemonic works in two ways, both of which describe subject and object pretty clearly. I, in this sentence, is the subject and is in the active voiceI is doing the loving here. You, on the other hand, is the receiver of this action, making this the object. This fact, of course, is further clarified by the mnemonic: You are the object of my affection. Quite literally, you is the object of I‘s affection. Such is love. Okay, moving on. Who and whom both function as pronouns but, in operation, they differ from each other much like subjects and objects do. Who operates as a subject– it is the I of the above mnemonic. Whom, in turn, operates as the object– the you. As such, their usage has to follow these functions; who completes the action and whom is the receiver. Here are some examples: Who stole my cheese? : The who, in this instance, is the one allegedly stole my cheese. Therefore, it is the subject. From whom did you steal that cheese? : Here, whom functions as the one who the cheese was stolen from; it is the receiver of the action,  steal. Therefore, it is the object. Following this, use whom when you are referring to the receiving object. So, the question “who do you think you are?” is correct. But, the questions “Who do you love?” and “Who do you voodoo?” are not. Another easy way to remember is to think of the answers to these questions and how they would relate to he or him Meaning, when I ask “From whom/who did you steal that cheese?” and you answer “from him,” then you know to use whom. Similarly, if you ask “Who/whom does he think he is?” and you answer “he think he’s the cat’s pajamas,” then you know to use who. Just remember: the –m in him should correspond with the -m in whom.