Which Is It? That? Or Which?
Now we open the proverbial can of worms.
Some people on earth know the differences between that and which. I’m one of them. So is your boss. Maybe.
Enough discerning readers out there do know the differences. So it’ll pay dividends for you to use these words correctly. Think of them as your tickets into a rather exclusive circle, if not The Writers’ Club itself.
You’ll have a general idea of the differences between that and which when you finish reading this section. But you won’t become a true expert until you read not only this section but the eBook Developing a Powerful Writing Style. There we’ll explore this matter more deeply. In fact, there you’ll learn the infamous Cow Pie-Chart Analysis. You may download Developing a Powerful Writing Style in our eBook section.
Restrictive and Nonrestrictive
First of all, both words introduce adjective clauses, that is, entire clauses that modify a noun in your sentence. Adjective clauses come in two basic models: restrictive clauses and nonrestrictive clauses. We might also refer to restrictive clauses as defining clauses and nonrestrictive clauses as nondefining clauses.
The word that introduces a restrictive clause. Ironically, this clause always answers this question: Which one? That one. Which book? That book.
The word which introduces a nonrestrictive clause. It must always be set off by commas.
That, Introduces Restrictive Clauses
Suppose the noun in your sentence is the noun books. Suppose you modify books with a restrictive clause. That restrictive clause takes a look at the noun books and says,
“Now, which books is this writer talking about? From the context of the stuff he has written so far, we don’t know the specific books he’s referring to.
“Therefore, this writer needs me to identify the precise books he’s talking about. Now watch me point out which books. Watch me define which books. Here I go,” says the restrictive clause.
Everybody should read the books that the critics recommend.
Here the clause that the critics recommend singles out which books the writer is talking about and defines them. Thus, the clause is a restrictive or defining clause.
Which, Introduces Nonrestrictive Clauses
Now suppose the writer has already revealed the identity of the books. From context the reader knows which books the writer is referring to. The writer might have written: “Children profit from the Harry Potter series.” And then the writer adds:
Now the clause is not identifying which books the writer is writing about. The reader already knows which books—the Harry Potter series. The clause, therefore, is not defining the books. The clause is thus nonrestrictive or nondefining. The correct relative pronoun is which, and the clause must be set off from the rest of the sentence by commas.
Do I need to repeat that, or does the bold type drive the point home?
We’ll explore the differences between that and which more thoroughly in the eBook Developing a Powerful Writing Style. After a while, you’ll automatically choose the correct word and punctuate the sentence with any necessary commas to set off any nonrestrictive clauses.
In that ebook, we’ll also see how the grandfathers of the plain-English movement, Messrs. Strunk and White, gave some very careless advice in their book, The Elements of Style, and as a result caused all sorts of problems.
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