Common Grammar Mistakes

The Most Frequent English Errors and How to Fix Them

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 in American English (use "is"), but standard in British English:

"The team are playing well."

✓ Standard in American English:

"The team is playing well."

Rule: Collective nouns (team, family, group) are treated as singular in American English. British English commonly treats them as plural. Choose one convention and apply it consistently throughout your document.

Who vs. Whom

⚠️ Informal but widely accepted in casual speech:

"Who did you give it to?"

✓ Preferred in formal writing:

"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). In everyday speech "who" is common in both positions; formal writing prefers "To whom did you give it?"

Best Learning Paths

Possessive vs Contraction

Start here for apostrophe-heavy mistakes like its/it's and your/you're.

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Exact Homophones Guide

Useful when your mistakes come from words that sound the same.

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English Punctuation Marks

Use this when comma, semicolon, colon, or apostrophe rules keep breaking your drafts.

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Core Sentence Rules

Best for sentence fragments, run-ons, agreement, and other structure-level issues.

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Time & Progression Words

Helpful when errors involve then/than, passed/past, and time-order wording.

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Prepositions & Spacing

Use this for one-word vs two-word traps like anytime/any time or setup/set up.

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If the issue is specific rather than broad, move directly to active versus passive voice for unclear actors, in, on, and at for time or place, continually versus continuously for repeated action, historic versus historical for past events, or hyphens and dashes for punctuation boundaries.

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