TOEFL 2026 guide

The fourteen grammar rules TOEFL Writing keeps testing

Every wrong option in a sentence task breaks one of a small number of rules. Here they are, with why each wrong form is the tempting one.

~9 min read · Updated 2026-08-22

Why fourteen and not a hundred

A sentence task gives you one wrong option, and that option is not wrong at random — it breaks a specific rule, chosen because that rule is one people actually get wrong. Across the whole practice bank, every wrong option falls into one of fourteen categories. The categories are not ours: they follow ERRANT, the standard framework for classifying grammatical errors, which separates subject–verb agreement from tense from non-finite form rather than calling all three “verb”.

The useful half is not the rule

You can know that a verb agrees with its subject and still pick the wrong one, because the subject is often not the nearest noun. So each rule below says why the wrong form is tempting, not only what the right one is. A trap you cannot see the appeal of will catch you again.

Agreement

Subject–verb agreement

The verb agrees with the subject, but the subject is often not the nearest noun. A phrase in between — “of artifacts”, “that the team collected” — leaves a plural sitting right before the verb, and the ear follows the closest word.

Find the subject before you choose the verb: cover everything between them and read the two words together.

“Not this: The collection of artifacts are on the upper floor.”

This: The collection of artifacts is on the upper floor. · singular subject + verb-s · plural subject + verb

Singular and plural nouns

A number or quantifier in front of the noun already says “more than one”, so the plural -s feels redundant — and in many languages it would be.

In English the noun marks number too, even when a number is already there. Say the number and the noun aloud together.

“Not this: three promising property”

This: three promising properties · three + plural noun · each / every + singular noun

Verb forms

Verb form

An -ing or to- form looks like a verb and carries the right meaning, so the sentence feels finished. It isn’t: those forms cannot be the main verb of a clause on their own.

Ask what the main verb of the clause is. If the only candidate ends in -ing or starts with to, something is missing — usually an auxiliary.

“Not this: The committee reviewing the attribution.”

This: The committee is reviewing the attribution. · modal + base form · be + -ing · have + past participle

Verb tense

The base form is the one you learned first and the one a dictionary shows, so it is what comes to mind under time pressure — even when the sentence has already announced its time with “yesterday” or “last week”.

Find the time expression first, then make the verb match it. The sentence usually tells you the tense before you have to choose it.

“Not this: The advisor approve my schedule change this morning.”

This: The advisor approved my schedule change this morning. · past time marker + past form · will / be going to + base form

Word choice

Word class

The two words share a stem and a meaning, so only the ending differs — and the ending is the part that carries the grammar. “Patient” and “patiently” mean the same thing and cannot go in the same place.

Ask what the word is doing, not what it means. Describing a verb needs -ly; naming a thing needs the noun form.

“Not this: The librarian patient helps students.”

This: The librarian patiently helps students. · adjective + noun · verb + adverb (-ly)

Word choice

Both words are correct English with almost the same meaning, so nothing sounds broken. What separates them is which words they are allowed to stand next to — you make a phone call, you do not do one.

Learn these as pairs, not as single words. The partner word is the thing to remember.

“Not this: Maria did a phone call to her advisor.”

This: Maria made a phone call to her advisor. · make a call · do the work · say something · tell someone

Articles and quantifiers

Articles

Articles carry almost no meaning you can hear, and many languages manage without them entirely, so they are the first thing to disappear under pressure. English uses them to mark whether the listener already knows which one you mean.

Ask whether the listener already knows which one. First mention takes a/an; a second mention, or something obvious from context, takes the. Uncountable nouns take neither.

“Not this: I need an pencil for the quiz.”

This: I need a pencil for the quiz. · a / an = first mention · the = already known · uncountable = no article

Quantifiers

Each pair means the same amount, so meaning gives you no help choosing. The split is grammatical: some quantifiers only go with things you can count, and some only with things you cannot.

Test the noun first: can you put a number in front of it? If yes, use many / few / fewer. If no, use much / little / less.

“Not this: The clerk delivered much packages.”

This: The clerk delivered several packages. · countable: many · few · fewer · uncountable: much · little · less

Prepositions

Prepositions rarely translate one-to-one, so the one that is right in your first language is often the one that feels right here. And several are genuinely arbitrary — English says good at, not good in, for no reason you can reason your way to.

Store the preposition with the word before it, as one unit — good at, arrive at, depend on. Do not translate it on its own.

“Not this: The dean speaks at 10 AM in Friday.”

This: The dean speaks at 10 AM on Friday. · at + clock time · on + a day · in + a month or year

Pronouns and reference

Pronouns

The pronoun points at something you are already thinking about, so its own form feels like a detail. But English changes that form depending on the job it is doing, and it must match the thing it points back to, not the nearest noun.

Replace the pronoun with the noun it stands for and read the sentence again. The wrong form usually becomes obvious.

“Not this: The dean gave they a certificate.”

This: The dean gave them a certificate. · subject: I · he · they · object: me · him · them · possessive: my · his · their

Relative pronouns

All of them introduce the same kind of extra information, so any one of them sounds plausible in the slot. The choice is decided by two things you have to look for: whether the thing is a person, and what job it does inside the clause.

Ask two questions in order: is it a person? Then, inside the clause, is it doing the action, receiving it, or owning something?

“Not this: Workers are repairing the bridge who crosses the river.”

This: Workers are repairing the bridge which crosses the river. · who = person doing · whom = person receiving · whose = owner · which / that = thing

Joining clauses

Connectors

Two connectors can express the same relationship and still not be interchangeable, because they attach to different things: because takes a whole clause, because of takes a noun. The logic is right and the grammar still fails.

Check what follows the connector. A full clause with its own subject and verb, or just a noun phrase? That decides which form you need.

“Not this: I didn't attend the meeting because of I was sick.”

This: I didn't attend the meeting because I was sick. · because + clause · because of + noun · as soon as + clause

Inverted conditionals

The if- version is correct English and means the same thing, so nothing warns you that it is wrong here. In formal writing the auxiliary moves in front of the subject and if disappears entirely — the structure carries the register.

When the sentence starts with had, were or should and no if, it is already a conditional. Do not add if back — the inversion is doing that job.

“Not this: If the discrepancies been flagged, the institution would not be facing an audit.”

This: Had the discrepancies been flagged, the institution would not be facing an audit. · Had + subject + past participle, … would have …

Comparison

Comparatives and superlatives

English marks comparison twice over — with an ending or with a separate word — and doubling both feels like emphasis rather than error. Comparative and superlative are also easy to swap, because both are simply “more”.

Mark it once. Short words take -er and -est; longer ones take more and most. Then check how many things you are comparing: two takes the comparative, three or more takes the superlative.

“Not this: Professor Patel is the most organized than Professor Liu.”

This: Professor Patel is more organized than Professor Liu. · two things: -er / more … than · three or more: the -est / the most

Practising them

Two games train these from opposite directions. Build a Sentence asks you to produce a correct sentence and names the rule when you miss; Spot Check shows you a finished sentence and asks whether it holds, against a clock.

Build a Sentence →Spot Check →