‘Which’ versus ‘that’: when to use them!

It’s time for another grammar rant from me. This one is about when to use “which” and when to use “that”. I see a lot of published documents—fiction and otherwise—that use them both (IMO) incorrectly.

Consider the following sentence:

I bought a car which is pink.

According to some grammar books, the “which” is wrong. According to others, it’s not incorrect but it’s also not the best choice of words because it leaves the reader to guess what you’re trying to say. Either way, it should be fixed.

Both “which” and “that” can be used to introduce a clause. But when they do, they flag different things to the reader. “Which” flags a non-defining clause: one that contains supplementary information not required by the main clause. “That” flags a defining clause: one that is part of your main message.

When used to introduce a clause, “which” requires a comma in front of it and “that” shouldn’t have one.

So, in the case of the car, if I’m trying to tell you a bought a car that happened to be pink, I’d say:

I bought a car, which is pink.

The information after the comma is supplementary, not essential to the sentence. But if I’m really excited about the fact my car is pink, and it’s the main focus of what I’m trying to say, then I’d use “that”:

I bought a car that is pink.

Of course, with a simple sentence like this I’d edit it further to tighten it up even more: I bought a pink car! But in a more complex example, such a rewrite isn’t possible to do elegantly. See below.

This is wrong:

I went into the bakery which sold egg-and-bacon pies and hot cross buns.

This is the non-defining clause (the bakery I went into happened to sell pies and buns):

I went into the bakery, which sold egg-and-bacon pies and hot cross buns.

This is the defining clause (I specifically went into a bakery that sold pies and buns as opposed to the one that sold, say, bread and sausage rolls—and why wouldn’t you?!):

I went into the bakery that sold egg-and-bacon pies and hot cross buns.

Mmm, egg-and-bacon pies…

…

Sorry, what were we talking about? :p