The English Grammar Rules People Look Up Most (and the Mistakes That Follow)

If you sit and watch what people actually type into a search bar, the same handful of grammar questions come up again and again. Not the exotic stuff about cleft sentences or the subjunctive in formal letters. The everyday traps: does the verb match the subject, is it a or an, did I use the right tense, where does the comma go, is it who or whom, and the one that trips up native speakers daily, its versus it's.

This post is a fast tour through those high-frequency rules. I kept it to the ones that matter for essays, emails, and exam writing, with one correct example and one common mistake for each. Think of it as a checklist you can run a sentence past before you hit send.

Subject-Verb Agreement: Match the Number

The core rule is simple to state and easy to forget under pressure: a subject and its verb must agree in number. A singular subject takes a singular verb; a plural subject takes a plural verb.

Correct: The list of items is on the desk.
Mistake: The list of items ~~are~~ on the desk.

The trap here is the noun sitting closest to the verb. Items is plural and right next to the verb, so your ear wants are. But the real subject is list, which is singular. Strip out the phrase between the subject and verb and the right choice becomes obvious: the list... is.

A few patterns that catch people:

Either/neither... or/nor: the verb agrees with the nearer subject. Neither the manager nor the clerks have signed it.
Indefinite pronouns like everyone, each, nobody are singular: Everyone is here, not are.
Collective nouns (team, family, committee) take a singular verb in American usage: The team is winning.

Articles: A, An, and The

Two questions cover almost all of it. First, a or an? The rule is about sound, not spelling: use "a" before a consonant sound and "an" before a vowel sound.

an honest mistake (the h is silent, so the word starts with a vowel sound)
a university (the u sounds like you, a consonant sound)
an MBA (the letter M is read em, a vowel sound)

So an hour but a hospital; a European but an umbrella. Trust your ear, not the first letter.

Second, the versus no article. Use the when both you and the reader know which specific thing you mean. Use a/an (or nothing, for plurals and uncountables) when you're introducing something for the first time. I bought a book yesterday. The book was about grammar. The first mention is new; the second points back to the known one.

Tense: Say When It Happened

Tense errors rarely break a sentence, but they make writing read as non-native. Two distinctions do most of the work.

Simple past vs. present perfect. Use the simple past for a finished action at a specific past time. Use the present perfect for an action connected to now, with no stated time.

Correct: I have seen that film. / I saw that film yesterday.
Mistake: I ~~have seen~~ that film yesterday.

The moment you add a finished-time word like yesterday, last week, or in 2019, the present perfect is wrong. Yesterday is over, so the action lives in the simple past.

The "main clause future, subordinate clause present" rule. After when, if, as soon as, and before, use the present tense even when you mean the future:

Correct: I'll call you when I arrive.
Mistake: I'll call you when I ~~will arrive~~.

Commas: The Four That Actually Matter

Comma rules sprawl, but four cover most real writing:

Before a coordinating conjunction joining two full sentences. I packed my bag, and I left. (Both sides could stand alone.)
After an introductory phrase. After the meeting, we went home.
Around non-essential information. My brother, who lives in Tokyo, is visiting. (Drop the middle and the sentence still works.)
Between items in a list. We bought apples, bread, and milk.

The classic error is the comma splice: joining two complete sentences with only a comma. It was late, ~~we went home~~ should be a period, a semicolon, or a comma plus so.

Word Pairs That Trip Everyone Up

These aren't grammar so much as memory, but they appear in search logs constantly.

its / it's. This is the big one. "Its" is possessive while "it's" means "it is" (or "it has"). The dog wagged its tail. It's raining. The apostrophe never marks possession here, which feels backwards because everywhere else it does.
who / whom. Who is the subject (it does the action); whom is the object (it receives it). Quick test: if you could answer with he, use who; if you'd answer with him, use whom. Who called? (He called.) To whom did you speak? (I spoke to him.) In everyday writing, who is increasingly accepted everywhere, but exam writing still rewards the distinction.
your / you're, their / there / they're, affect / effect follow the same pattern: a contraction or a homophone masquerading as the word you want.

A Worked Example: Fixing One Sentence

Here's a sentence with two of the most common errors stacked together:

The team have lost it's first match.

Two problems. First, subject-verb agreement: team is a collective noun, singular in standard usage, so it takes has, not have. Second, its/it's: the writer wants the possessive (the match belonging to the team), so it should be its with no apostrophe. It's would expand to it is first match, which is nonsense.

The corrected sentence:

The team has lost its first match.

I run my own writing through exactly this two-step check. When I draft fast, its/it's slips through more than any other error, so I do a final pass where I expand every it's to it is in my head. If the sentence still makes sense, the apostrophe stays; if it doesn't, I delete it. That one habit caught more mistakes for me than any grammar app ever did, because it forces me to read what I actually wrote instead of what I meant.

Where to Go From a Question to an Answer

A list like this is a map, not the territory. When you're stuck on a specific point, browsing 60-plus rules with side-by-side correct and incorrect examples beats scrolling a flat 200-item dump with no explanation. The English Grammar Rules Reference groups rules by category, marks the common-mistake line in pink with a strikethrough, and gives a bilingual "why" for each one, so you learn the reason instead of memorizing a verdict.

Grammar is only half the battle, though. The other half is which words actually go together, since rules tell you a sentence is legal, not that it sounds natural. Make a decision is right; do a decision is grammatical nonsense to a native ear. For that, pair this with the English Collocations reference and you'll cover both the structure and the word choice that make writing read like a native wrote it.

Run a sentence past the six checks above, fix the one or two things that fail, and most of your everyday grammar problems are already solved.

Made by Toolora · Updated 2026-06-13