One of the grammar issues I see writers struggle with most is when to use “that” or “which.” Here is the big question you have to ask of the sentence to determine which one to use: does that clause have to be there for the sentence to make sense in context?
If so, it’s a restrictive clause and you need a “that.”
If not, use “which.”
And yes, I hear you asking “what the hell is a restrictive clause, Sarah? Are we going full grammar class mode here?” (Oh, we sure are.) Restrictive clauses are acting as adjectives to describe something about the noun that precedes it. It’s showing specificity – it’s that particular noun that the clause is modifying and without it, we wouldn’t be able to identify what specific thing it was.
Let’s see an example of a restrictive clause:
He honked at the car that entered the intersection.
He honked at the car which entered the intersection.
Here we need a restrictive clause because we’re speaking about the specific car, the one entering the intersection. If we didn’t have this clause pointing to the noun, we wouldn’t have enough context to identify which car on the road the sentence means.
Another example with a non-restrictive clause:
In this novel, which follows the story of a young woman, the author develops her signature style.
In this novel, that follows the story of a young woman, the author develops her signature style.
The commas are a good clue here that we need to use “which” (and yes, more often than not, you’ll usually need a comma before the “which”), but more to the point, the clause “which follows the story of a young woman” is non-restrictive and is not essential to the sentence. Presumably, we already know in context which novel is being discussed (the “this” is pointing to something that would have come in a previous sentence), so all the clause is doing is adding a bit of extra detail. The sentence would work just fine without it: “In this novel, the author develops her signature style.”
So context is really important to determine when to use “that” or “which.” What must your reader know?
She put on shoes that gave her four inches of extra height.
She put on shoes, which gave her four inches of extra height.
Is it important that she put on shoes that made her taller, or is it important that she put on shoes, period? That’s the difference between these two sentences, either of which could be correct, depending on what you need to get across.
I hope this will help eradicate the “that”/”which” problem in your own writing!