10 Common English Grammar Mistakes (And How to Fix Them)

1. Its vs. Its

"Its" is possessive (The company increased its revenue). "It's" is a contraction of "it is" (Its a great day). This is the most common grammar error in professional writing.

2. Your vs. Youre

"Your" shows possession (Your report is ready). "You're" means "you are" (You're hired). Spell-checkers often miss this mistake.

3. There vs. Their vs. Theyre

"There" refers to a place (over there). "Their" shows possession (their office). "They're" means "they are" (they're coming). When in doubt, expand the contraction.

4. Affect vs. Effect

"Affect" is usually a verb (The weather affects my mood). "Effect" is usually a noun (The effect was immediate). A simple trick: affect = action, effect = end result.

5. Fewer vs. Less

Use "fewer" for countable items (fewer errors) and "less" for uncountable quantities (less time). This rule applies to most professional writing contexts.

6. Who vs. Whom

Use "who" for the subject of a sentence (Who wrote this?) and "whom" for the object (To whom should I send this?). In casual writing, "who" is increasingly accepted for both.

7. Then vs. Than

"Then" refers to time (First this, then that). "Than" is used for comparisons (Better than before). A common mix-up even among native speakers.

8. Me vs. I

Use "I" as the subject (Sarah and I went) and "me" as the object (Between you and me). A quick test: remove the other person from the sentence.

9. Alot vs. A Lot

"A lot" is two words. "Alot" is not a word. This simple misspelling can undermine the professionalism of your writing.

10. Could of vs. Could Have

"Could have" (or the contraction "could've") is correct. "Could of" is always wrong. The same applies to should of, would of, and might of.

How to Catch These Errors

Use an AI writing assistant like TMOAD to catch these mistakes automatically. It checks grammar, spelling, and style in real time as you type.