A noun clause is a dependent clause that functions as a noun, so it can act as a subject, direct object, object of a preposition, or subject complement. Unlike a phrase, a noun clause contains its own subject and verb, but it cannot stand alone as a complete sentence.
Key Facts
A noun clause contains a subject and a verb but depends on another clause.
Noun clauses commonly begin with that, what, who, whether, if, how, why, when, or where.
A noun clause can function as a subject, direct object, object of a preposition, or subject complement.
Embedded questions use statement word order: I know where she is, not I know where is she.
Whether works before an infinitive and after a preposition; if generally does not.
The mandative subjunctive uses the base verb after words such as demand, recommend, insist, and require.
What Is a Noun Clause?
A noun clause is a subordinate clause that fills a position normally occupied by a noun or noun phrase. In I know the answer, the noun phrase the answer is the direct object; in I know what the answer is, the noun clause what the answer is fills the same grammatical position.
The clause has internal structure. What the answer is contains the subject the answer and the verb is, while what connects the embedded clause to the main sentence. The complete sentence remains grammatical because what the answer is depends on I know.
The traditional substitution test is useful: replace the clause with it, something, or someone. For example, She explained why the machine failed becomes She explained it. The substitution confirms the object function, although it does not identify every boundary perfectly.
Noun Phrase or Noun Clause?
| Feature | Noun phrase | Noun clause | Example |
|---|---|---|---|
| Internal verb | Usually absent | Present | the result / what caused the result |
| Dependency | Can function independently in a sentence role | Depends on a main clause | The result mattered / What caused it mattered |
| Typical introducer | Determiner or modifier | that, what, whether, who, how | the decision / whether they agreed |
| Replacement | it, something, someone | it, something, someone | I know the fact / I know that she left |
How Do Noun Clauses Work?
Noun clauses embed a proposition, question, identity, or choice inside a larger sentence. The main clause supplies the grammatical frame, while the subordinate clause supplies information that functions as a participant in that frame.
In The manager confirmed that the shipment had arrived, confirmed is the main verb and that the shipment had arrived is its direct object. In Whether the shipment arrived remains unclear, the entire clause is the subject of remains.
Noun clauses often communicate information rather than naming a physical object. They are especially common after verbs of thinking, knowing, reporting, discovering, deciding, explaining, and remembering.
Which Words Introduce Noun Clauses?
| Introducer | Main meaning | Example |
|---|---|---|
| that | Reported fact or proposition | We believe that the plan will work. |
| what | The thing or information that | She described what she saw. |
| who, whom | Person or people | I know who called. |
| whoever, whomever | Any person meeting a condition | Give it to whoever arrives first. |
| whether | Alternative or uncertainty | We must decide whether we should stay. |
| if | Embedded yes-or-no question | I asked if the store was open. |
| how, why, when, where | Method, reason, time, or place | Explain how the system works. |
The introductory word may perform a role inside the clause. In what she bought, what is the object of bought. In who called, who is the subject. By contrast, that is normally a conjunction and does not perform a subject or object role.
What Functions Can Noun Clauses Perform?
Noun clauses perform four core syntactic functions, with adjective complements often taught alongside them because they complete the meaning of an adjective. The function depends on the clause’s position and its relationship to the surrounding verb, preposition, or adjective.
| Function | Diagnostic position | Example | Replacement |
|---|---|---|---|
| Subject | Before the main verb | What she decided surprised us. | It surprised us. |
| Direct object | After a transitive verb | They discovered that the valve was closed. | They discovered it. |
| Object of preposition | After a preposition | We argued about whether the rule applies. | We argued about it. |
| Subject complement | After a linking verb | The issue is that funding is limited. | The issue is it. |
| Adjective complement | After an adjective | I am certain that the figures are correct. | I am certain of it. |
Subject Noun Clauses
A subject noun clause occupies the subject position and controls the relationship with the main verb. What the witness remembered changed the investigation means that the remembered information produced the change.
Subject clauses are grammatical but can make sentences heavy, particularly when they contain several modifiers. Writers often use it as a temporary subject and move the noun clause to the end: It changed the investigation what the witness remembered is not idiomatic, but It was surprising that the witness remembered the detail is natural.
Direct-Object Noun Clauses
Direct-object clauses follow verbs that take information, beliefs, questions, or decisions as their objects. Common verbs include know, think, believe, report, explain, ask, decide, remember, discover, and confirm.
- The engineer confirmed that the test had passed.
- I cannot remember where I parked.
- The committee debated whether the proposal was affordable.
- She explained why the sensor had failed.
The conjunction that can often be omitted after a reporting verb: I think that he is ready and I think he is ready are both grammatical. Keeping that improves clarity when the sentence contains a long subject or several consecutive verbs.
Objects of Prepositions
A noun clause can follow a preposition when the clause expresses the object of discussion, concern, disagreement, or another relationship.
- They disagreed about what the contract required.
- The result depends on whether the sample was contaminated.
- We are concerned with how the policy affects tenants.
A key restriction separates whether from if. Standard formal English permits whether after a preposition, as in It depends on whether the supplier responds. It does not normally permit if in the same construction.
Predicate Nominatives and Subject Complements
A noun clause after a linking verb identifies, defines, or explains the subject. In The difficulty is that the files are incomplete, the clause explains the meaning of the difficulty.
The term predicate nominative is most precise when the complement renames the subject, as in The question is who authorized the payment. Some grammar references use the broader term subject complement because the clause may explain rather than literally rename the subject.
How Can You Identify a Noun Clause?
Use five tests in sequence: locate the verbs, separate the clauses, find the introducer, identify the clause’s sentence role, and test a replacement. The replacement should preserve the grammatical structure, not necessarily preserve every shade of meaning.
- Locate every verb. In I know where the files are, the verbs are know and are.
- Separate the clauses. The main clause is I know; the subordinate clause is where the files are.
- Find the boundary marker. Here, where introduces the embedded question.
- Check the internal subject and verb. The files is the subject and are is the verb.
- Replace the clause. I know it confirms that the clause is the direct object.
Do not classify a clause solely by its first word. Where the files are is a noun clause in I know where the files are, but a relative clause in the room where the files are stored, because the second example modifies room.
How Are Noun Clauses Different From Other Dependent Clauses?
A noun clause fills a noun position, a relative clause modifies a noun, and an adverbial clause modifies a verb, adjective, or entire clause. The same word, including where or when, can introduce different clause types depending on its grammatical function.
| Clause type | What it modifies or fills | Example | Main test |
|---|---|---|---|
| Noun clause | Noun position | I know what she wants. | Replace with it. |
| Relative clause | A preceding noun | I found the book that she wanted. | Ask which noun it describes. |
| Adverbial clause | Verb, adjective, or clause | Call me when she arrives. | Ask when, why, how, or under what condition. |
| Comparative clause | Degree or comparison | It is larger than I expected. | Completes a comparison. |
Compare these sentences:
- I remember when the train arrived. The clause is the object of remember, so it is a noun clause.
- I left when the train arrived. The clause gives the time of left, so it is an adverbial clause.
- The time when the train arrived was recorded. The clause modifies time, so it is a relative clause.
This distinction matters because punctuation and interpretation follow function, not merely the introductory word.
What Is the Correct Word Order in Embedded Questions?
Embedded questions use normal statement order after the question word. The formula is question word + subject + verb, not the inverted order used in a direct question.
| Direct question | Embedded noun clause |
|---|---|
| Where is the office? | I know where the office is. |
| Why did she leave? | We asked why she left. |
| What does the device measure? | Tell me what the device measures. |
| Has the payment cleared? | I wonder whether the payment has cleared. |
The auxiliary do, does, or did usually disappears because embedded questions do not use direct-question inversion. I do not know where does he work is incorrect; I do not know where he works is correct.
A noun clause can still contain an auxiliary when the auxiliary has independent grammatical work: I wonder where he has gone and I wonder whether he can attend are both correctly formed.
When Should You Use If or Whether?
Use if for many informal embedded yes-or-no questions, but use whether when the sentence presents alternatives, follows a preposition, precedes an infinitive, or requires a more formal construction.
- I asked if the meeting was canceled. Informal and grammatical.
- I asked whether the meeting was canceled. Formal and grammatical.
- We must decide whether to postpone. Correct; if to postpone is not standard.
- It depends on whether the permit is approved. Correct after a preposition.
- She could not say whether the fault was electrical or mechanical. Correct for explicit alternatives.
In careful academic and professional writing, whether is usually the safer choice. If also introduces conditional adverbial clauses, so whether reduces ambiguity in sentences such as We need to know whether the server is online.
Can That Be Omitted From a Noun Clause?
The conjunction that may be omitted when it introduces a direct-object clause after many reporting and thinking verbs. The omission does not change the clause’s meaning: She said that the package arrived and She said the package arrived are equivalent.
Keeping that is preferable when omission could create a misreading:
- Clear: The analyst reported that the figures were incomplete.
- Potentially dense: The analyst reported the figures were incomplete after the audit.
The conjunction cannot be omitted when the clause is the subject or subject complement in standard formal usage:
- That the data were altered became obvious.
- The concern is that the data were altered.
Do not confuse conjunction that with demonstrative that or relative that. In I know that the report is late, that introduces a noun clause. In the report that arrived late, that introduces a relative clause modifying report.
How Does the Mandative Subjunctive Work?
The mandative subjunctive uses the base form of the verb after expressions of demand, recommendation, necessity, and insistence. The form stays the same for all subjects: The board recommended that he leave, not that he leaves.
- The doctor insisted that she rest.
- The policy requires that every applicant submit identification.
- They recommended that the company reduce exposure.
- The judge ordered that the records be released.
The pattern is especially common in American English and formal institutional writing. British English also uses should in comparable contexts: The committee recommended that he should leave. The should construction is grammatical, but mixing forms creates an error: recommended that he should leaves is incorrect.
The subjunctive expresses the desired action, not necessarily a factual event. That distinction separates The manager insisted that he leave from The manager confirmed that he left.
What Punctuation Do Noun Clauses Require?
Noun clauses do not normally receive commas merely because they are dependent clauses. A comma depends on position, interruption, and readability rather than on the noun-clause label.
- No comma: I know what the report contains.
- No comma: The fact is that the report contains errors.
- Introductory subject clause: What the auditor discovered, however, surprised the board.
- Commas around interruption: What the auditor discovered, according to the minutes, surprised the board.
A long introductory noun clause may be followed by a comma when the boundary improves readability: Whether the contractor can finish before winter, remains uncertain is often punctuated this way by writers, but many style guides omit the comma because the clause is the grammatical subject. The cleaner revision is It remains uncertain whether the contractor can finish before winter.
What Are Common Noun-Clause Errors?
Most noun-clause errors involve confusing clause function, using direct-question order, or adding a second subject pronoun. The fastest correction method is to identify the embedded clause’s internal subject and verb before changing punctuation or word order.
| Error | Incorrect form | Correct form | Reason |
|---|---|---|---|
| Inverted embedded question | I know where is my phone. | I know where my phone is. | Use statement order. |
| Double subject | What he wrote it was useful. | What he wrote was useful. | The clause already is the subject. |
| Wrong subjunctive form | They demanded that she applies. | They demanded that she apply. | Use the base verb. |
| If after preposition | It depends on if he agrees. | It depends on whether he agrees. | Use whether after a preposition. |
| Misidentified relative clause | I read what the editor changed article. | I read what the editor changed. | What means “the thing that.” |
How Do You Avoid Double Subjects?
A noun clause functioning as a subject already fills the subject position. What the researcher found was significant is correct; What the researcher found it was significant contains an unnecessary second subject.
The same principle applies to pronoun repetition after a direct object: I know what she wants, not I know what she wants it. A pronoun can appear inside the noun clause, but it cannot duplicate the clause as a whole.
What Is the Difference Between What and That?
What means approximately “the thing that” and performs a role inside its clause. That introduces a proposition but normally performs no internal role.
- I understand what she meant. She meant what.
- I understand that she was upset. She was upset; that only introduces the proposition.
- What he proposed was expensive. The proposal was expensive.
- That he proposed it was surprising. The fact of his proposal was surprising.
This distinction prevents a common error: I know that he wants is incomplete unless wants has an understood complement, while I know what he wants is complete because what is the object of wants.
How Are Noun Clauses Used in Formal Writing?
Noun clauses allow formal writers to package claims, evidence, uncertainty, and recommendations into precise grammatical units. Academic reports frequently use them after reporting verbs, while scientific prose uses them to distinguish observations from interpretations.
Common patterns include:
- The results indicate that the treatment reduced symptoms.
- It is likely that the sample was contaminated.
- The study examined whether sleep duration affected recall.
- What the findings cannot establish is causation.
- The evidence suggests that the variables were correlated.
The anticipatory it pattern, as in It is believed that the policy will reduce costs, places a heavy clause at the end and makes the sentence easier to process. However, excessive passive reporting can hide responsibility. The researchers concluded that the policy reduced costs is more direct than It was concluded that costs were reduced.
How Should You Practise Noun Clauses?
A practical progression takes roughly 1-2 hours to understand and 1-2 weeks of deliberate writing practice to use consistently, although accuracy depends on the learner’s command of verb tense, clause boundaries, and question formation.
- Convert noun phrases into that clauses: I know the result becomes I know that the test failed.
- Convert direct questions into embedded questions: Where is the station? becomes I know where the station is.
- Write one example for each syntactic function.
- Underline the main verb once and the noun-clause verb twice.
- Check whether if should be replaced with whether.
- Read the sentence aloud and remove any repeated subject pronoun.
Beginners should start with direct objects after know, think, and say. Intermediate learners should focus on embedded questions and what clauses. Advanced writers should practise mandative subjunctives, extraposition, and concise reporting structures.
Frequently Asked Questions
Can a noun clause begin with a question word?
Yes. What, who, why, how, when, and where can introduce noun clauses when the resulting clause fills a noun position. In She explained why the alarm sounded, the clause is the object of explained. In Leave when the alarm sounds, when the alarm sounds is an adverbial clause because it modifies leave.
Is “that” always a noun-clause marker?
No. That can introduce a noun clause, a relative clause, or a demonstrative phrase. In I believe that the plan works, it introduces a noun clause. In the plan that works, it introduces a relative clause modifying plan. In that plan works, it functions as a demonstrative determiner.
Can a noun clause be a complete sentence?
No. A noun clause is dependent and cannot normally express a complete independent thought by itself. What she decided is a noun clause, while What she decided surprised everyone is a complete sentence because the main clause supplies the required independent structure.
Do noun clauses need commas?
Usually not. Direct-object clauses and subject complements generally take no comma: I know that the figures are correct and The problem is that the figures are incomplete. Commas may surround an interrupting expression or follow a long introductory clause when a particular style guide recommends the pause.
Are “whoever” and “whomever” interchangeable?
No. Use whoever when the word is the subject of its clause and whomever when it is the object. Give the award to whoever wins uses whoever as the subject of wins. Give it to whomever the committee selects uses whomever as the object of selects.
What is the simplest noun-clause test?
Replace the suspected clause with it, something, or someone, then check whether the sentence retains the same grammatical role. The test works best for object and complement clauses, but function and meaning should also be checked against nearby nouns and verbs.
The Bottom Line
A noun clause is a dependent clause that functions like a noun while containing its own subject and verb. Identify it by its internal clause structure and external role, then distinguish it from relative and adverbial clauses by asking whether it fills a noun position, modifies a noun, or supplies information about time, cause, condition, or manner. Mastering these tests makes noun clauses accurate in everyday speech and formal writing.
