Good writers make grammar mistakes too. Most of them aren’t gaps in knowledge. They happen when you’re typing quickly and two words sound alike, or a rule you learned years ago gets a little fuzzy.
The good news is that a handful of mix-ups cause most of the trouble. Learn a simple test for each one and you’ll catch them in emails, essays and reports before anyone else does.
1. Its vs. it’s
It’s always means “it is” or “it has.” Its shows possession, like his or her.
- It’s raining again. (It is raining.)
- The company changed its logo. (The logo belongs to the company.)
The test: Replace the word with “it is.” If the sentence still makes sense, use it’s. If not, use its.
2. Your vs. you’re
You’re is short for “you are.” Your means something belongs to you.
- You’re going to love this.
- Is this your jacket?
The test: Say “you are” out loud. “You are going to love this” works. “Is this you are jacket?” doesn’t, so it’s your.
3. There, their and they’re
- There points to a place or introduces something: Put it over there. There are three options.
- Their shows possession: They forgot their tickets.
- They’re means “they are”: They’re running late.
The test: If you can swap in “they are,” use they’re. If something belongs to them, use their. Everything else is usually there, which contains the word here, another place word.
4. Affect vs. effect
In most sentences, affect is a verb (an action) and effect is a noun (a result).
- The cold weather affected our plans.
- The cold weather had a big effect on our plans.
The trick: Remember RAVEN: Remember, Affect is a Verb, Effect is a Noun.
There are rare exceptions. Effect can be a verb meaning “to bring about” (to effect change), but in everyday writing the RAVEN rule will steer you right.
5. Then vs. than
Then is about time or sequence. Than is for comparisons.
- We ate dinner, then went for a walk.
- This route is faster than the highway.
The trick: Than and compare both have an a. Then and time both have an e.
6. Who vs. whom
Who does the action. Whom receives it.
- Who called you? (Who is doing the calling.)
- To whom should I send this? (The email goes to them.)
The test: Answer the question with he or him. If the answer is he, use who. If it’s him, use whom. Both him and whom end in m.
- Who/whom called? → He called. → Who.
- Who/whom did you invite? → I invited him. → Whom.
In casual writing, many people use who everywhere, and that’s usually fine. In formal writing, it’s worth getting right.
7. Fewer vs. less
Use fewer for things you can count one by one. Use less for amounts you measure.
- Fewer cars, fewer mistakes, fewer emails.
- Less traffic, less water, less time.
The test: If you could put a number in front of it (three cars), use fewer. If you couldn’t (three traffics), use less.
You’ll still see “10 items or less” on grocery store signs. Strictly speaking, it should be “10 items or fewer.”
8. Me vs. I (and “between you and I”)
People often reach for I because it sounds more formal, even when me is correct.
- Sarah and I went to the meeting.
- The manager invited Sarah and me.
- Keep this between you and me.
The test: Remove the other person. “The manager invited I” sounds wrong, so it’s Sarah and me. “I went to the meeting” sounds right, so it’s Sarah and I.
After words like between, with, for and to, use me.
9. Comma splices
A comma splice joins two complete sentences with only a comma.
- ❌ The meeting ran long, we missed the train.
Each half could stand on its own, so a comma isn’t strong enough to hold them together. You have a few easy fixes:
- Use a period: The meeting ran long. We missed the train.
- Add a joining word: The meeting ran long, so we missed the train.
- Use a semicolon: The meeting ran long; we missed the train.
The test: If both sides of the comma could be their own sentences, you need more than a comma.
10. Could of, should of, would of
These come from how we speak. Could’ve sounds like could of, but the correct phrase is could have.
- ❌ I should of called.
- ✅ I should have called. or I should’ve called.
The same goes for would have, might have and must have. Of is never correct after these words.
Bonus: a few spelling traps
Some words get misspelled so often that the wrong version starts to look right:
- Definitely, not definately. It contains the word finite.
- Separate, not seperate. There’s a rat in separate.
- Receive, not recieve. I before e, except after c.
- Necessary: one collar and two sleeves.
- Accommodate: it’s big enough to accommodate two cs and two ms.
How to make the fixes stick
Reading a list of rules helps, but the mistakes usually come back when you’re writing quickly. A few habits make the difference:
- Read your writing out loud. Your ear catches problems your eyes skip over.
- Search for your personal trouble spots. If you know you mix up affect and effect, search for both before you send something important.
- Practice a little and often. Short, regular quizzes help the right choice become automatic. That works better than one long study session.
Practice with Aloquent (coming soon)
We’re building Aloquent, an iPhone and iPad app for practicing grammar, vocabulary and spelling in short lessons. Each lesson comes with a quick quiz, and the four levels go from high school basics to college writing. Every mistake in this article is the kind of thing it helps you practice.
Aloquent isn’t on the App Store yet. Visit the Aloquent page to see what’s coming, and check back for the launch.
Frequently asked questions
What is the most common grammar mistake?
Mixing up words that sound alike is the most common, especially its and it’s, your and you’re, and there, their and they’re. Spell checkers often miss them because each word is spelled correctly. It’s just the wrong word for the sentence.
Is it ever correct to say “between you and I”?
In standard written English, no. Between should be followed by me, so the correct phrase is between you and me. You’ll hear “between you and I” in conversation, but it’s best avoided in formal writing.
Can I start a sentence with “and” or “but”?
Yes. Many teachers discourage it, but it isn’t a grammar rule, and good writers do it all the time. Just don’t overuse it.
How can I improve my grammar quickly?
Focus on the few mistakes you make most often instead of trying to memorize every rule. Learn one simple test for each one, read your writing out loud before sending it, and practice in short sessions rather than one long one.
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