Here are few tests to identify a noun clause in a sentence. A particular method may not conclusively tell if the clause is noun, so it’s advisable to apply more than one to be doubly sure.
This post covers how to identify noun clause. Learn how to identify other dependent clauses as well. (In case you’re used to seeing only three dependent clauses, there are four.)
1. Is the marker word one that introduces a noun clause?
(A marker word, also called introductory word, introduces or begins a dependent clause.)
Noun clauses are introduced by marker words that, if, whether, who, whom, whose, what, which, when, where, why, and how.
If the marker word of the dependent clause under investigation is from the above list, the dependent clause could be a noun clause.
Since the number of marker words are limited, you can memorize them all, but beware an introductory word that introduces noun clause may introduce relative or adverb clause as well. But this limitation is not difficult to overcome as only few introductory words overlap. Only when, where, if, and whether introduce noun clause as well as adverb clause. And only who, whom, whose, that, which, when, where, and why introduce noun clause as well as relative clause. (The two links take you to examples of how each marker word can introduce two different clauses.)
Another challenge with this approach is that a noun clause may not even have a marker word.
1.1. A noun clause may not have a marker word
The marker word that can be left out in noun clauses under certain conditions. Examples:
We heard (that) they were leaving early. [that can be dropped]
Scientists believe (that) Covid is going to stay with us for at least few years.
How do you identify them without a marker word?
When you see a sentence-like unit (Covid is going to stay with us for at least few years) immediately after a reporting verb (believe, say, tell, mention, know, think, etc.), it’s a noun clause with that dropped.
This comes with a small caveat though. Marker words can be dropped in relative clause too, leading to a dependent clause that looks like a sentence. (Unlike noun clause though, in relative clause almost all marker words can be dropped.) But here the relative clause follows a noun phrase – and not a verb. Examples:
The email (that) you sent never arrived.
The man (whom) she was talking to is her brother.
2. Is the sentence incomplete after dropping the clause?
If the answer is yes, it’s a noun clause?
Adjectives and adverbs are modifiers. Without them, a sentence will still be a sentence, though with less details. But without a noun, a sentence would not make sense. None of these sentences, for example, can stand if we drop the clause, implying they’re noun clauses.
What you did was beyond our wildest expectations.
The captain was undecided on which team to field for today’s match.
The answer isn’t what you think.
The police finally found who was behind the crime. [It may look like a sentence, but it’s not. The verb lacks direct object: The police finally found what?]
The expert committee told the government that urgent steps are required to boost the economy. [Here too the verb lacks direct object: The expert committee told the government what?]
Let’s try dropping the clause in few more sentences. If the sentence doesn’t make sense, it would be a noun clause. Otherwise not.
What you decide is entirely up to you. [Noun clause]
I believe she can finish the project on time. [Noun clause. I believe what? Note the absence of marker word, which we covered in the last section.]
They wondered whether he would attend the meeting. [Noun clause. They wondered what?]
I’m a living example of the dictum that an hour in the morning is worth two in the evening. [It can stand as a sentence, implying it’s not a noun clause. It’s a relative clause.]
When I’m not focusing on something, I get lost in thoughts. [It can stand as a sentence, implying it’s not a noun clause. It’s an adverb clause.]
3. Can the clause be replaced by a noun or pronoun?
If the answer is yes, it’s a noun clause.
Because a noun clause functions like a noun, we should be able to replace it with a noun (including a noun phrase) or pronoun without disturbing the sentence grammatically. Let’s do this in the examples we saw earlier.
It was beyond our wildest expectations.
The police finally found him.
The captain was undecided on it.
The answer isn’t zero. [A noun replacing the clause.]
They all make meaningful sentences. Since the clauses can be replaced by nouns or pronouns, they’re noun clauses.
4. Does the clause follow a verb and/or pose an indirect question?
If yes, it’s a noun clause.
A clause immediately after a verb will most likely be a noun clause functioning as object of the verb. And you can be almost certain if the verb is a reporting verb (a verb that merely reports someone’s work) such as say, tell, mention, believe, reply, ask, know, think, respond, order, admit, deny, and complain. This, in fact, happens to be the most common use of noun clause.
The police finally found who was behind the crime. [Immediately after a verb + indirect question]
We need to rethink how we train our students. [Immediately after a verb + indirect question]
These four charts show who is ahead in the race to best year-end performance. [Immediately after a reporting verb + indirect question]
The newspaper reports that the government is planning a relief package for the industry. [Immediately after a reporting verb. Of all the marker words introducing noun clause, only that can’t ask a question.]
An adverb clause too can sometimes follow a verb.
He had left when I reached there.
I’ll not leave unless you agree to approve the project.
But here the clauses aren’t object of the verb. They’re merely stating time and condition, respectively, that govern the main clause. You can confirm the above clauses as adverb by applying other tests to identify an adverb clause (see link at the beginning of the post).
4.1. Exception
The clause though may not immediately follow verb if the sentence contains an indirect object. In this sentence, for example, the indirect object the government comes in between the reporting verb told and the clause.
The expert committee told the government that urgent steps are required to boost the economy.
Don’t confuse the above clause with the relative clause. Like the above clause, a relative clause comes immediately after a noun or noun phrase, but the above clause is not a relative clause as it is not describing the government.
5. Does the clause follow a preposition?
If the answer is yes, it’s a noun clause.
A preposition can be followed only by a noun or noun phrase. Hence, a clause following a preposition will always be a noun clause. In this sentence, for example, the clause follows the preposition on. Hence, it’s a noun clause.
The captain was undecided on which team to field for today’s match.
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6. Rule out other dependent clauses
You can also identify a noun clause by ruling out the possibility of other three dependent clauses. How do you do that? Refer to the posts on how to identify noun, adverb, and comparative clause linked to earlier.
To end, while applying above tests, remember what was mentioned at the beginning of the post: A particular test may not conclusively tell if the clause is relative. It’s better to apply more than one to be doubly sure.
