A noun clause is a noun, not a modifier, so it doesn’t hang from anything. Like a gerund (Diagrams: Participles, Gerunds and Infinitives), it stands on a forked stand in the place a noun would go: subject, direct object, predicate noun or object of a preposition. It keeps its own baseline on top of the stand. This builds on Diagrams: Adjective and Adverb Clauses.
Key idea
A noun clause stands on a stand in a noun’s place. A word like that or whether, which only introduces the clause, sits on a line above it; a word like what or who, which does a job inside the clause, goes in that job’s place.
Why it works
The stand shows the clause doing a noun’s job in the main sentence while keeping its own subject and verb. It is the same idea as a gerund on its stand: something bigger than a word, used as one noun.
Worked example: A noun clause as predicate noun
Diagram “My hope is that the rain stops.”
- Main baseline: hope | is, with My under hope.
- The clause renames hope: it is the predicate noun, after the slanted line.
- It stands on a stand there: rain | stops, the under rain, and that above.
Answer: hope | is \ [that] rain | stops
Common mistake
Attaching a noun clause with a dotted line as if it were a modifier. Use the “something” test: “I know something.” The clause is the object itself, so it stands in the object’s place.
Textbooks draw a few details differently (the angle of a slant, where a conjunction sits). These lessons use the usual form, as in Reed and Kellogg’s Higher Lessons in English and most American grammars; if your book differs a little, both are fine.