15 Grammar Mistakes Even Good Writers Make (With Fixes)

I have been a professional writer for 12 years. I still make grammar mistakes. Not the obvious ones — I know the difference between "their" and "there." The mistakes I make are the subtle ones that even spell-checkers miss. Here are 15 that I catch in my own writing and in the writing of other experienced professionals.

1. Dangling Modifiers

Wrong: "Walking to the office, the rain started pouring."
Right: "Walking to the office, I got caught in the rain."

The modifier "walking to the office" needs to attach to a person, not to "the rain." Rain does not walk. This error is everywhere — in newspapers, corporate emails, and published books.

2. Comma Splices

Wrong: "The report is ready, send it to the client."
Right: "The report is ready. Send it to the client." (or use a semicolon)

Two independent clauses joined by just a comma. Fix with a period, semicolon, or conjunction.

3. Who vs. Whom

Quick test: If you can replace it with "he/she," use "who." If you can replace it with "him/her," use "whom."

"Who wrote this?" (He wrote this.) "To whom should I send it?" (Send it to him.)

4. Less vs. Fewer

"Less" for uncountable things (less water, less time). "Fewer" for countable things (fewer files, fewer errors). "10 items or less" at the grocery store is technically wrong.

5. Effect vs. Affect

"Affect" is usually a verb (the change affected our workflow). "Effect" is usually a noun (the effect was significant). Exception: "effect" as a verb means "to bring about" (effect change).

6. Misplaced "Only"

"I only eat vegetables on Monday" means I do nothing else with vegetables on Monday — I do not cook them, sell them, or throw them. "I eat vegetables only on Monday" means Monday is the only day I eat them. Position matters.

7. Subject-Verb Agreement with Collective Nouns

"The team is working" (American English, team as a unit). "The team are working" (British English, team as individuals). Both are correct in their respective dialects. Pick one and be consistent.

8. Parallel Structure

Wrong: "She likes reading, to write, and editing."
Right: "She likes reading, writing, and editing."

Items in a list should follow the same grammatical pattern.

9. That vs. Which

"That" introduces essential information (restrictive clause): "The file that you sent is corrupted."
"Which" introduces non-essential information (non-restrictive clause): "The file, which you sent yesterday, is corrupted."

10. Apostrophe in "Its"

"Its" (no apostrophe) = possessive. "It's" (apostrophe) = "it is." This trips up everyone because possessives usually have apostrophes, but "its" is an exception (like "his" and "hers").

11. Ending Sentences with Prepositions

"Where is the file at?" The "at" is unnecessary. "Where is the file?" is cleaner. But "This is something I will not put up with" is fine — restructuring it ("This is something up with which I will not put") sounds absurd.

12. Literally vs. Figuratively

"I literally died laughing" — no, you did not. "Literally" means it actually happened. Use "figuratively" or just drop the word entirely.

13. Could Of / Should Of

"Could of" is always wrong. It is "could have" (or "could've"). The confusion comes from how "could've" sounds when spoken.

14. Run-On Sentences

A sentence that keeps going and going without proper punctuation or conjunctions it just runs together and becomes hard to read and the reader loses track of the point. Break long sentences into shorter ones.

15. Passive Voice Overuse

"The report was written by the team" (passive) vs. "The team wrote the report" (active). Passive voice is not wrong, but overusing it makes writing weak and unclear. Use the Grammar Checker to identify passive constructions.

How to Catch These

1. Run your text through the Grammar Checker — it catches most of these
2. Read your writing aloud — your ear catches what your eye misses
3. Let it sit for a day, then re-read with fresh eyes
4. Use the Readability Checker to identify overly complex sentences

Related Tools

As writing experts note, grammar rules exist to serve clarity. When a rule makes writing clearer, follow it. When following a rule makes writing awkward, break it intentionally.