Madeleine L’Engle’s A Wrinkle in Time introduces readers to three very eccentric immortals that are always getting to scrapes: Mrs. Who, Mrs. Which, and Mrs. Whatsit. If you have read this wonderful book (and if you haven’t, you should!) then you understand how difficult it can be to tell these ladies apart; however, it may be easier to differentiate between them than to keep up with “that,” “which,” and “who”!
A grammatical issue that many people have to look up, as evidenced by how quickly it appeared as I typed it into Google, the issue of “that” versus “which” versus “who” is actually quite simple to understand. With a bit of help (I have turned to The Blue Book of Grammar and Punctuation), you will easily be telling them apart—though the Blue Book can’t help you on the Mrs. Who, Mrs. Which, and Mrs. Whatsit front.
Who
This rule is simple, though people often overlook it: “Who” is only used if it is referencing a person.
Wrong: “The company who donated to the charity was generous.”
Right: “The woman who donated to the charity was generous.”
That
Unfortunately, the rule for “that” is not as cut and dry as the rule for “who,” but it is relatively simple: Use “that” if the clause it introduces is essential.
Now, to brush up on your clause knowledge, essential clauses are those that are imperative to the meaning of the sentence. Without them, you wouldn’t know what “that” refers to.
Wrong: “The sweater which she brought to my house is dirty.”
Right: “The sweater that she brought to my house is dirty.”
The clause is essential because without the information it presents you would not know what sweater is being discussed.
Which
“Which” is used to introduce a clause after an essential clause, regardless of if it is essential or nonessential. Oftentimes, “which” is omitted to simplify a sentence, and of course it is a word that is used in other contexts, but when debating between “who,” “which,” and “that,” use “which” when the clause is nonessential or when it follows an essential clause that has already been introduced with a “this,” “that,” “these,” or “those.”
Wrong: “That is the very question that you must answer.”
Right: “That is the very question which you must answer.”
Right: “The sweater in the hallway, which she dropped, is dirty.”
Keep in mind, when determining whether or not a clause is essential or nonessential, that essential clauses will not be offset by commas, while nonessential clauses often will.
Keeping these grammatical rules straight may be a bit difficult at first, but much like the way you eventually learn the personalities of Mrs. Who, Mrs. Which, and Mrs. Whatsit, you will certainly learn to use these words properly with a bit of practice.
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