TOEFL Grammar: Advanced clause structure 10 hard-level rules, each shown with a correct sentence, the mistake learners most often make instead, and the TOEFL tasks where it counts.
Test Ninjas Research · Updated October 1, 2026
Reduced relative clauses, opening participles, appositives and inversion compress information into fewer words. Academic passages use them heavily, so recognizing them helps reading, and a few of them in your own writing can show range — as long as each one is correct.
Part of the
TOEFL grammar guide : 120 rules in 12 topics. The cards are original teaching material checked against the linked references; they are not an ETS syllabus.
The rules 1. Active reduced relative An -ing participle phrase can give information about a noun that an active relative clause could express.
Correct The students presenting the project arrived early.
Common trap · incorrect The students presented the project arrived early.
What goes wrong: the trap uses “presented” where the correct sentence has “presenting”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Participle clauses
2. Passive reduced relative A past-participle phrase can give information about a noun that a passive relative clause could express.
Correct The data collected in April are incomplete.
Common trap · incorrect The data collecting in April are incomplete.
What goes wrong: the trap uses “collecting” where the correct sentence has “collected”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Participle clauses
3. Opening participle and subject The noun after an opening participial phrase should be the person or thing doing that action.
Correct Walking into the lab, I noticed the alarm.
Common trap · incorrect Walking into the lab, the alarm sounded.
What goes wrong: the trap uses “alarm sounded” where the correct sentence has “I noticed alarm”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Dangling modifiers and how to correct them
4. Noun clause as one subject Treat a whole what-clause naming one fact as a singular subject.
Correct What the survey shows is a single pattern.
Common trap · incorrect What the survey shows are a single pattern.
What goes wrong: the trap uses “are” where the correct sentence has “is”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Emphasis: cleft sentences, inversion and auxiliaries
5. Appositive punctuation Set off a nonessential renaming phrase with commas on both sides when it interrupts a sentence.
Correct Dr. Chen, the lab director, approved the plan.
Common trap · incorrect Dr. Chen, the lab director approved the plan.
What goes wrong: the trap gets the punctuation wrong, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Appositives
6. Nonrestrictive which Use which, not that, to introduce a nonessential relative clause set off by commas.
Correct The archive, which opened in May, is nearby.
Common trap · incorrect The archive, that opened in May, is nearby.
What goes wrong: the trap uses “that” where the correct sentence has “which”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Relative clauses: defining and non-defining
7. Preposition before which When a preposition stands before a relative pronoun for a thing, use which rather than that.
Correct The process on which we relied was slow.
Common trap · incorrect The process on that we relied was slow.
What goes wrong: the trap uses “that” where the correct sentence has “which”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Which
8. Subject relative pronoun Do not omit a relative pronoun when it is the subject of its clause.
Correct The article that discusses migration is useful.
Common trap · incorrect The article discusses migration is useful.
What goes wrong: the trap leaves out “that”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Relative clauses: defining and non-defining
9. Whether-clause order After whether introduces an embedded question, keep subject-before-verb order.
Correct The question is whether the policy will change.
Common trap · incorrect The question is whether will the policy change.
What goes wrong: the trap uses the same words in a different order, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Whether
10. Negative-adverb inversion After a fronted negative adverb such as rarely, place the auxiliary before the subject.
Correct Rarely have I seen such clear results.
Common trap · incorrect Rarely I have seen such clear results.
What goes wrong: the trap uses the same words in a different order, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Emphasis: cleft sentences, inversion and auxiliaries
Previous ← Reference and comparison Next Conditionals and modality → Other grammar topics
Frequently Asked Questions Which TOEFL tasks test advanced clause structure? + No task names grammar topics, but these rules matter most in Build a Sentence, Academic Discussion. Build a Sentence rewards correct word order and forms directly; in emails, discussion posts and spoken answers, errors here make your meaning harder to follow.
Are these official TOEFL grammar rules? + No. ETS does not publish a grammar syllabus. These are original Test Ninjas teaching cards based on standard English usage, with links to the reference pages each rule was checked against.
How should I practice these rules? + Read the rule, then cover the correct sentence and try to fix the trap yourself. Next, write one new sentence of your own that follows the rule, ideally about a campus or class situation.