(Answer: when it’s a relative clause!)
One of my colleagues and I just had one of those “tell me I’m not going crazy” conversations about noun clauses. Intrigued? Mildly curious? A noun clause is a structure that isn’t obvious to native speakers of English unless they teach ESL, read grammar books for fun, or take linguistics classes. Essentially, it’s a complete finite clause (subject + verb + complements if needed) introduced by a subordinator (that, if, whether, or a wh- word) that can be used as a subject, object, or object of a preposition (for more, see Grammar Choices, Unit 3). For example:
- I know that grammar is exciting. (object of the verb know)
- That grammar is exciting should be self-evident. (subject of the sentence, but very rare)
- I’m interested in why you find grammar exciting. (object of a preposition)
Also, noun clauses are used as complements of a small number of nouns such as fact, belief, opinion:
- The belief that grammar is exciting has spread around the world.
However, it turns out that (here comes a noun clause) some internet sources are confusing noun clauses and relative clauses (aka adjective clauses). For instance, one site gives this puzzling example:
A person who trusts no one can’t be trusted. (Jerome Blattner)
(This noun clause is the subject of the sentence.)
The site suggests that this analysis is controversial. Not really: in this sentence, who trusts no one is not a noun clause. It can only be a relative clause modifying the head noun person.
But they are almost right: there is a gray area here, but it only arises if you try to delete the head noun (person):
- ?Who trusts no one can’t be trusted. (the ? indicates a questionable sentence)
Or to use a more familiar phrase:
- Who laughs last laughs longest.
I’ve always analyzed who laughs last as noun clause because it has no head (aagh! headless clauses!) and it functions by itself as a clausal subject of the main verb (the second laughs). But Celce-Murcia and Larsen-Freeman in The Grammar Book call this structure a free relative, which sounds like the uncle who won’t stop talking at Thanksgiving. And this makes sense because the structure seems to work better when it looks like an object relative clause, as another colleagues pointed out:
- Who trusts no-one can’t be trusted.
- Where you go I will go.
- Which class students choose depends on the time, location, and teacher.
The problem with this analysis is that I think it could encourage students to produce sentences like this, which I hear a lot:
- *Who buys and sells commodities is a trader.
Therefore, for the purposes of teaching, I stick by my original explanations:
- In the absence of a head noun, embedded clauses are noun clauses functioning as subjects, objects, or objects of prepositions (e.g. What I mean is that the website is wrong. What the author does is confusing. It depends on who[m] you ask.) Yes, there is a small structural difference between these sentences, but they quack like noun clauses.
- When the subordinator clearly has the function of a pronoun and is embedded within a noun phrase, it’s a relative clause, whether or not it can be substituted by a free relative (e.g. A person who buys and sells commodities is called a trader. The books which I consulted agree with me.)
- When a clause complements a noun rather than modifying it, we have a noun clause (e.g. The fact that we’re having this conversation is slightly terrifying due to the fact that people are backing away from me.)