Which is that
Which is that?
By Tony Spencer-Smith
In my grammar courses, one of the questions people often ask is whether to use that or which in a sentence.
I try to answer all questions in class, because if people are troubled by something it means they have thought about it and worried about it, and really want to know the answer. But this one is trickier than most to answer, so I have to brace myself!
I’ll start by asking you a question. Should it be: “I am looking for the file, which contains the latest invoices.” or “I am looking for the file that contains the latest invoices”?
The right word choice depends on whether the file is being defined by the information you are giving about it; in other words, whether it is specifying the file you are looking for, or simply giving additional information about it.
This distinction between essential and non-essential information is the key to this grammar conundrum.
If the listener does not know which file you are talking about, you need to use that, because the clause “that contains the latest invoices” defines what file is being sought, and so is essential to the meaning of the sentence.
Which is used to introduce a clause which gives you additional but not essential information, as in: “The tree, which had wonderful green leaves in spring, was an oak.” Here, the tree in question is already known to the reader. The essential information is that it is an oak; the fact that it is very green in spring is simply additional information.
Note that there is no comma before that, but there is one before which. This is another signal to the reader whether the clause is essential or non-essential.
A neat trick to make sure if you have made the right choice of word is to see whether the clause could be removed entirely from the sentence without destroying its meaning. If it can, then which is correct.
As you can see, when you understand the distinction the choice of words becomes obvious.
What I try to do in teaching grammar and punctuation is to explain things in the simplest way, avoiding complex grammar terminology wherever possible. I like people to finish the course thinking: wow, that’s not so hard after all!
Tony Spencer-Smith is an award-winning novelist, a former Editor-in-Chief of Reader’s Digest Magazine and an experienced corporate writer and writing trainer. His book The Essentials of Great Writing was published in Sydney in 2009.