Common Grammar Mistakes

Even experienced writers make these common mistakes. Learning to recognize them will dramatically improve your writing. Our free grammar checker can catch most of these automatically.

Start With the Highest-Frequency Mistakes

Mistake	Quick Rule	Best Full Lesson
Its vs It's	It's means it is or it has. Its is possessive.	Its vs It's
Your vs You're	You're means you are. Your shows possession.	Your vs You're
Their / There / They're	Possession vs place vs they are.	Their vs There vs They're
Then vs Than	Then is usually time. Than is comparison.	Then vs Than
Affect vs Effect	Affect is usually a verb. Effect is usually a noun.	Affect vs Effect
Comma mistakes	Do not join two full sentences with only a comma.	Comma Rules

Commonly Confused Words

Want detailed rules? Start with Its vs It's, Your vs You're, and Their vs There vs They're.

Its vs. It's

❌ Wrong:

"The dog wagged it's tail."

✓ Correct:

"The dog wagged its tail."

Rule: "It's" always means "it is" or "it has." "Its" is possessive (showing ownership). If you can replace it with "it is," use "it's."

Your vs. You're

❌ Wrong:

"Your going to love this."

✓ Correct:

"You're going to love this."

Rule: "You're" means "you are." "Your" shows possession. Test by expanding to "you are"—if it makes sense, use "you're."

Their, There, They're

❌ Wrong:

"Their going to there house."

✓ Correct:

"They're going to their house."

Rules:

Their = possessive (their house, their car)
There = location (over there, there is)
They're = they are (they're coming)

Then vs. Than

❌ Wrong:

"This is better then I expected."

✓ Correct:

"This is better than I expected."

Rule: "Than" is for comparisons (bigger than, better than). "Then" is for time sequences (first this, then that).

Affect vs. Effect

❌ Wrong:

"The rain will effect the game."

✓ Correct:

"The rain will affect the game."

Rule: "Affect" is usually a verb (to influence). "Effect" is usually a noun (the result). Remember: Affect = Action, Effect = End result.

Lose vs. Loose

❌ Wrong:

"Don't loose your keys."

✓ Correct:

"Don't lose your keys."

Rule: "Lose" (one O) = to misplace or fail to win. "Loose" (two O's) = not tight. Think: "Loose" has room for two O's because it's not tight!

Punctuation Mistakes

For full punctuation lessons, see Comma Rules, Semicolon Usage, and Apostrophe Rules.

Comma Splices

❌ Wrong:

"I love writing, it's my passion."

✓ Correct:

"I love writing. It's my passion."

"I love writing; it's my passion."

"I love writing—it's my passion."

Rule: Don't join two complete sentences with just a comma. Use a period, semicolon, or em dash instead.

Apostrophe in Plurals

❌ Wrong:

"I bought three apple's."

✓ Correct:

"I bought three apples."

Rule: Apostrophes show possession or contractions, NOT plurals. Just add "s" or "es" for plurals.

Grammar Mistakes

Practice these patterns with Subject-Verb Agreement, Who vs Whom, and Tense Consistency.

Subject-Verb Agreement

❌ Wrong:

"The team are playing well."

✓ Correct:

"The team is playing well."

Rule: Collective nouns (team, family, group) are usually singular in American English. The verb should match.

Who vs. Whom

❌ Wrong:

"Who did you give it to?"

✓ Correct:

"Whom did you give it to?"

"To whom did you give it?"

Rule: Use "who" for subjects (who did this?) and "whom" for objects (to whom?). Tip: If you can answer with "him," use "whom" (both end in M).

Check Your Writing Automatically

Run a quick check now, then open the linked full lesson for any mistake that keeps repeating.

Try Grammar Checker Free

Start With the Highest-Frequency Mistakes

Commonly Confused Words

Its vs. It's

Your vs. You're

Their, There, They're

Then vs. Than

Affect vs. Effect

Lose vs. Loose

Punctuation Mistakes

Comma Splices

Apostrophe in Plurals

Grammar Mistakes

Subject-Verb Agreement

Who vs. Whom

Best Learning Paths

Possessive vs Contraction

Exact Homophones Guide

English Punctuation Marks

Core Sentence Rules

Time & Progression Words

Prepositions & Spacing

Check Your Writing Automatically