TOEFL Grammar: Agreement and parallelism 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
Long subjects, each, a number of versus the number of, and items in a list that must match in form. These rules get harder as sentences get longer, which is why they matter most in academic writing and in longer Build a Sentence items.
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. Intervening phrases A phrase between subject and verb does not change the subject's number.
Correct The list of readings is online.
Common trap · incorrect The list of readings are online.
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: Subject-Verb Agreement
2. Each as subject Use a singular verb when each is the subject.
Correct Each participant has a code.
Common trap · incorrect Each participant have a code.
What goes wrong: the trap uses “have” where the correct sentence has “has”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Subject-Verb Agreement
3. Subjects joined by and Two distinct singular subjects joined by and normally take a plural verb.
Correct The professor and the assistant are here.
Common trap · incorrect The professor and the assistant is here.
What goes wrong: the trap uses “is” where the correct sentence has “are”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Subject-Verb Agreement
4. Mixed subjects joined by nor When singular and plural subjects are joined by nor, the verb normally agrees with the nearer subject.
Correct Neither the tutors nor the professor is available.
Common trap · incorrect Neither the tutors nor the professor are available.
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: Subject-Verb Agreement
5. One of plus plural noun Use a plural noun after one of when choosing a member of a group.
Correct One of the reasons is cost.
Common trap · incorrect One of the reason is cost.
What goes wrong: the trap uses “reason” where the correct sentence has “reasons”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Countability: one of
6. A number of plus plural verb A number of followed by a plural count noun normally takes a plural verb.
Correct A number of students are waiting.
Common trap · incorrect A number of students is waiting.
What goes wrong: the trap uses “is” where the correct sentence has “are”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Number
7. The number of plus singular verb The number of names a single quantity and normally takes a singular verb.
Correct The number of unread messages on the course forum is falling.
Common trap · incorrect The number of unread messages on the course forum are falling.
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: Number
8. No repeated relative subject Do not add a second subject pronoun after a relative pronoun that already acts as subject.
Correct The report that explains the method is concise.
Common trap · incorrect The report that it explains the method is concise.
What goes wrong: the trap adds “it”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Relative Pronouns
9. Parallel items in a list Use comparable grammatical forms for items serving the same role in a list.
Correct The course teaches reading, writing, and speaking.
Common trap · incorrect The course teaches reading, writing, and to speak.
What goes wrong: the trap uses “to speak” where the correct sentence has “speaking”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Source: Parallel Structure
10. Not only and but also Keep the structures after not only and but also parallel when they are paired.
Correct The course requires not only reading but also writing.
Common trap · incorrect The course requires not only reading but also to write.
What goes wrong: the trap uses “to write” where the correct sentence has “writing”, so it no longer follows the rule.
Matters for: Build a Sentence · Academic Discussion
Sources: Not only ... but also ; Parallel Structure
Previous ← Academic cohesion and punctuation Other grammar topics
Frequently Asked Questions Which TOEFL tasks test agreement and parallelism? + 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.