I'm preparing for academic IELTS by writing some essays and then correcting those using a grammar correction app.
In the following sentence,
Outside there is a money receiver which only accepts coins
The app suggests using "that" instead of "which". But is "which" also acceptable, or is it a critical mistake?
In prescriptive English, "which" should only introduce non-restrictive relative clauses, those that are offset by a comma and aren't intrinsic to the subject, but give more information about it. Your example uses a restrictive clause, so "that" is the better option. (There are plenty of resources that go into detail on relative clauses, should you need it.)
This rule is purely prescriptivist, and native English speakers ignore it all the time. It is usually observed in formal writing though, so you're definitely best off learning it and using it "properly" in your exam.
In this context, I think "that" and "which" are completely interchangeable and either one is completely acceptable.
the-baby-is-you's answer states that "In prescriptive English, 'which' should only introduce non-restrictive relative clauses." I never heard of such a prescription before today, and I think that using "which" for restrictive relative clauses (which is what the phrase "money receiver which only accepts coins" does) is very common in skilled, careful writing.
In order to try to verify this, I decided to look through the opinions of the Supreme Court of the United States in Obergefell v. Hodges (2015). I found 12 usages of "which" for a restrictive relative clause which could have been written using "that" instead. Out of these, most of them were original text, but there were also multiple usages in quotes from the 18th century, and multiple from the 19th century as well.
I admit that some sources say that "which" shouldn't be used restrictively, such as this Grammarly page that Barmar posted a link to in a comment on this answer. On the other hand, this page at merriam-webster.com, linked to by zhantongz, points out that "which" has been used restrictively since the "youth" of the English language, and that any rules against such usage were made artificially and never really caught on.
Personally, I think that the long history of use of restrictive "which" by skilled, careful writers is proof that it's totally fine. Other people disagree.
One issue is this:
It is extremely unlikely that an English speaker, in spoken English, would say
Outside there is a vending machine ...
They would say
There's a vending machine outside ...
given that, it's true that
There's a vending machine outside that only takes coins.
would be used far more than
There's a vending machine outside which only takes coins.
However
The formulation is extremely unrealistic. Any English speaker would say
There's a vending machine outside, but it only takes coins.
You would only use the very unrealistic formulation from the question, in this extremely unusual situation:
"Hmm, most vending machine take both credit cards and coins. I wonder if there exist any vending machines that only take coins?" "You won't believe it! There's a vending machine right outside that only takes coins!"
Other than in that bizarre example, there's no reason an English speaker would say
There's a vending machine outside that only takes coins.
they would say
There's a vending machine outside, but it only takes coins.
Outside there is a money receiver which only accepts coins.
I think the app is right that "that" is marginally more realistic than "which" in this sentence... but the sentence has much much bigger issues, which it would be good to address! I would write:
The vending machine outside doesn't take anything but coins.
First of all, "a money receiver" isn't a thing, at least not in America. I infer that we're talking about some kind of machine that accepts coins — maybe a parking meter, or a vending machine. But the phrase "money receiver" just makes me think of Polonius's advice in Hamlet — "neither a money giver nor a money receiver be," I think it was? ;)
Secondly (and the first thing I noticed, because I'm like this) is that the modifier "only" is misplaced in the original sentence. Obviously a money receiver would only accept coins! A machine that produced coins would be called something else.
I infer that the narrator was actually trying to say that "the machine accepts only coins"; that is, it doesn't accept bills (or "banknotes," to a Brit) or credit cards or whatever. It accepts only coins.
But in real life, if I'm telling someone about this machine, I wouldn't say that it "accepts only coins"; I would be warning the listener against some specific course of action that they might be about to try. For example, if I see them going outside with a dollar bill in hand, I might call out, "Hey, that machine doesn't take bills!" ("Really?" "Yeah, it only takes coins." Once we get down into the colloquial register, I admit that even I will naturally misplace the word "only," because to do otherwise sounds just as stilted and awkward as talking about "money receivers" or using the verb "accept" to mean "take as input.")
Finally, the formulation "There is a Y which blahs" strikes me as a bit of a Spanglish-ism. In English we'd generally just say "The Y blahs." Especially, we force the subject toward the beginning of the sentence. If I'm listing all the outdoor facilities at this location, sure: "Outside there's a vending machine, an ice chest, and a water hookup." But if I'm giving you advice about the vending machine, I would make it the subject of the sentence: "The vending machine outside is a little flaky."
Put all these minor flaws (and fixes) together, and you get:
The vending machine outside doesn't take anything but coins.
