25 Grammar Mistakes Professionals Make (With Fixes)

Common grammar mistakes appear in professional writing every single day — in emails, slide decks, client proposals, and performance reviews. The writers making them aren’t careless; they’re often sharp people who learned certain patterns early and never got corrected. If you want to understand your grammar patterns at a deeper level, that’s a good place to start. Here, the goal is more direct: 25 specific mistakes, the wrong version, the right fix, and one clear reason each one matters.

The 5 Pronoun Mistakes That Appear Most Often

Pronouns are small words doing large jobs. When they’re wrong, readers pause — and that pause costs you credibility.

1. Their / There / They’re Wrong: Their going to present there findings at the conference. Right: They’re going to present their findings at the conference. These three words sound identical but serve entirely different purposes — they’re is a contraction of “they are,” their marks possession, and there indicates location.

2. Its / It’s Wrong: The company revised it’s strategy after it’s Q3 review. Right: The company revised its strategy after its Q3 review. It’s always means “it is” or “it has” — if you can’t expand it into one of those phrases, the apostrophe doesn’t belong.

3. Who vs. Whom Wrong: Who did you send the proposal to? Right: Whom did you send the proposal to? Substitute him or her into the answer — if “him” fits (“I sent it to him”), then whom is correct in the question.

4. I vs. Me in Compound Objects Wrong: Please send the report to Jessica and I. Right: Please send the report to Jessica and me. Remove the other person from the sentence — you wouldn’t say “send the report to I,” so me is the right choice.

5. Reflexive Pronoun Overuse (Myself) Wrong: Please contact myself if you have any questions. Right: Please contact me if you have any questions. Myself is a reflexive pronoun that should only appear when “I” has already been used in the sentence — it’s not a polite or formal substitute for me.

Which Common Grammar Mistakes Do the Most Damage?

Some of the most persistent common grammar mistakes aren’t about sentence structure at all — they’re about choosing between two words that look or sound similar.

6. Affect vs. Effect Wrong: The new policy will effect how we handle onboarding. Right: The new policy will affect how we handle onboarding. Affect is almost always a verb meaning to influence; effect is almost always a noun meaning the result — “the effect was immediate.”

7. Fewer vs. Less Wrong: We received less complaints this quarter than last. Right: We received fewer complaints this quarter than last. Use fewer for things you can count individually (complaints, errors, meetings); use less for amounts measured in bulk (less time, less effort).

8. Ensure / Insure / Assure Wrong: We want to assure quality on every deliverable. Right: We want to ensure quality on every deliverable. Ensure means to make certain something happens; insure relates to financial coverage; assure is used when you’re putting someone’s mind at ease.

9. Complement vs. Compliment Wrong: The new layout compliments the brand’s visual identity. Right: The new layout complements the brand’s visual identity. Complement means to enhance or complete something; compliment means to praise — only one belongs in a design review.

10. Principal vs. Principle Wrong: Our principle concern is client satisfaction. Right: Our principal concern is client satisfaction. Principal means primary or main (also a school administrator); principle refers to a rule or belief — “our core principles guide every decision.”

If you notice you’re making the same word-pair errors across multiple documents, that’s a habit, not a one-time slip. NotchTutor tracks which mistakes you repeat over time — not just flagging an error once, but identifying recurring patterns so you can address the root cause. You can also run your writing through a grammar checker built for professionals for real-time feedback before anything goes out the door.

Verb Errors That Quietly Undermine Your Writing

11. Lay vs. Lie Wrong: I need to lay down before the afternoon presentation. Right: I need to lie down before the afternoon presentation. Lie means to recline and takes no object; lay means to place something and requires an object — “lay the document on the table.”

12. Lead vs. Led Wrong: She lead the integration project from kickoff through launch. Right: She led the integration project from kickoff through launch. The past tense of lead is led, not lead — the confusion comes from the word “lead” (the metal), which is spelled the same but pronounced differently.

13. Subject-Verb Agreement with Collective Nouns Wrong: The committee are still reviewing the budget proposal. Right: The committee is still reviewing the budget proposal. In American English, collective nouns — team, committee, staff, board — take singular verbs, even though they refer to multiple people.

14. Double Negatives Wrong: We don’t have no timeline confirmed for the rollout. Right: We don’t have a timeline confirmed for the rollout. Two negatives cancel each other out in standard English, creating a logical contradiction — your sentence ends up meaning the opposite of what you intended.

Common Grammar Mistakes in Punctuation

Punctuation errors are often the most visible common grammar mistakes in professional writing because they alter the rhythm of a sentence in ways that feel off even to readers who can’t name the rule.

15. Comma Splices Wrong: The deadline is Friday, please submit your work by noon. Right: The deadline is Friday; please submit your work by noon. A comma alone can’t join two independent clauses — use a semicolon, a period, or a coordinating conjunction like and or but.

16. Apostrophes in Plurals Wrong: All CEO’s and CFO’s are expected to attend the offsite. Right: All CEOs and CFOs are expected to attend the offsite. Apostrophes signal possession or mark contractions — they don’t form plurals, even for abbreviations or acronyms.

17. Semicolon Misuse Wrong: We reviewed three vendors; but selected the original one. Right: We reviewed three vendors, but selected the original one. A semicolon joins two independent clauses — it should never appear directly before a coordinating conjunction like but, and, or so.

18. Oxford Comma Ambiguity Wrong: I want to thank my mentors, Sarah and Tom. Right: I want to thank my mentors, Sarah, and Tom. Without the Oxford comma, the sentence implies Sarah and Tom are your mentors — adding it clarifies that they’re three separate people you’re thanking.

Sentence Structure Errors Worth Correcting

19. Dangling Modifiers Wrong: Having reviewed the proposal, several issues were identified. Right: Having reviewed the proposal, the team identified several issues. The introductory phrase must logically connect to the sentence’s subject — “several issues” can’t review a proposal.

20. Run-On Sentences Wrong: The launch ran over schedule we didn’t hit our targets we need to regroup. Right: The launch ran over schedule. We didn’t hit our targets, so we need to regroup. Run-on sentences bury your key points and signal rushed thinking — breaking them into clean, separate statements is always clearer.

21. Sentence Fragments Wrong: Delivered the final report on Thursday. Without any revisions required. Right: We delivered the final report on Thursday, with no revisions required. A sentence needs both a subject and a verb — fragments feel incomplete and undermine the professional tone you’re trying to build.

22. Passive Voice Overuse Wrong: Mistakes were made during the product rollout. Right: The project team made mistakes during the product rollout. Passive voice isn’t inherently wrong, but using it to obscure who did what reads as evasive and makes business writing harder to act on.

Commonly Confused Words That Fool Even Strong Writers

23. Comprise vs. Compose Wrong: The report is comprised of five sections. Right: The report comprises five sections. (Or: Five sections compose the report.) Comprise means “to contain” — the whole comprises the parts, not the reverse; “is comprised of” is widely considered incorrect.

24. Further vs. Farther Wrong: We’ll discuss this further at a farther date. Right: We’ll discuss this further at a later date. Farther refers to measurable physical distance; further refers to degree, extent, or time — “further discussion,” not “farther discussion.”

25. That vs. Which Wrong: The clause which defines the payment terms is missing. Right: The clause that defines the payment terms is missing. Use that to introduce a restrictive clause — information essential to the sentence’s meaning — and which (preceded by a comma) for non-restrictive clauses that add context without changing meaning.

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Catching these common grammar mistakes is the first step. The harder part is making the corrections automatic. For context-specific help, the guides on email grammar mistakes and grammar mistakes that hurt credibility at work are worth reading alongside this one — different settings surface different patterns. Work through one group at a time, review your past writing for recurring errors, and the improvements will compound quickly.