I need a milk butler. “Need?” you ask, followed by, “What’s a milk butler?” Feel free to replace those question marks with interrobangs if you want.
Every morning I eat cereal, then I drink tea. Both activities require adept milk pouring skills. Have you ever opened a brand new gallon of milk and thought to yourself, “Now what?” Inevitably, you mis-pour the milk and have a cascade of milk down the side of the milk container, only some of which ends up in your bowl. And, when it comes to tea, a milk-pouring catastrophe is the quickest way to end up with way too much milk in your tea. So — yes — I need a milk butler. I just can’t afford one yet.
In the same way that I struggle with pouring milk, many people struggle with knowing the right time to use “that” and “which.” I’m just going to hit you with the punchline on this one: if your sentence doesn’t need the clause your word (that or which) is joining, use which. If your sentence does need the clause your word (that or which) is connecting, use that. It’s as simple as that.
Now for some examples. Here are two nearly identical sentences:
My milk butler’s DeLorean, which is painted space gray, gets up to 88 miles per hour quite quickly.
My milk butler’s DeLorean that is painted space gray gets up to 88 miles per hour quite quickly.
This is a tale of two sentences. In the first sentence, I implied that the milk butler (whose name is Percy) only has one DeLorean, and it just happens to be painted space gray. The detail about the paint color isn’t necessary, so I chose to use “which.” Removing the phrase “which is painted space gray” doesn’t change the meaning of the sentence, but simply adds a nice detail to the already intriguing sentence.
In the second sentence, however, you get the impression that Percy owns multiple DeLoreans. The phrase “that is painted space gray” is an example of a restrictive clause; another part of the sentence (My milk butler’s DeLorean), depends on it. If you remove “that is painted space gray,” the meaning of the sentence changes completely.
Do I need a milk butler? Probably so, but my finances don’t yet allow for it. Until then, I’ll just have to make sure I’m using “that” and “which” correctly.