The 15 Grammar Mistakes That Make Your Writing Look Amateur

Tier one: mistakes readers treat as character evidence

These five are the expensive ones. They live in constructions taught since grade school, they cannot be blamed on autocorrect, and they cluster in exactly the documents where you are being judged.

1. "It's" where "its" belongs. The apostrophe form is a contraction of "it is." The possessive never takes one.

• Wrong: The company quietly changed it's refund policy.
• Right: The company quietly changed its refund policy.

The same family covers your/you're, their/there/they're, and whose/who's. A spelling checker will not save you here, because every form is a real word. The full mechanics live in our guide to apostrophes.

2. The comma splice. Two independent sentences joined by nothing stronger than a comma.

• Wrong: The report is due Friday, please send your section by noon.
• Right: The report is due Friday. Please send your section by noon.

Readers feel the joint give even when they cannot name the problem. Our guide to comma rules that actually matter covers the full repair toolkit.

3. Subject-verb drift. The verb wanders off to agree with the nearest noun instead of the real subject.

• Wrong: The list of requirements were lost in the migration.
• Right: The list of requirements was lost in the migration.

The subject is "list," not "requirements." When the verb agrees with the wrong noun, the sentence wobbles audibly. The genuinely hard cases get their own treatment in our subject-verb agreement guide.

4. The dangling modifier. An opening phrase that latches onto whatever noun happens to come next.

• Wrong: Walking into the office, the coffee machine greeted me.
• Right: Walking into the office, I found the coffee machine already running.

The machine did not walk in. You did. Dangling modifiers manufacture accidental comedy, and comedy in a quarterly review is rarely intentional.

5. "Between you and I." Prepositions take object pronouns: me, him, her, us, them.

• Wrong: Between you and I, the rollout is doomed.
• Right: Between you and me, the rollout is doomed.

Nobody writes "between I" on its own. The pair is a disguise, and hypercorrection reads as performed formality, which is its own kind of tell.

Tier two: mistakes that blur your meaning

The second tier will not get you dismissed, but it makes readers reread, and rereading is where goodwill goes to die.

6. The run-on sentence. Two independent clauses fused with no punctuation at all.

• Wrong: I applied for the job it seemed like a good fit.
• Right: I applied for the job because it seemed like a good fit.

Unlike the comma splice, the run-on offers no visible stumble, which is why it survives proofreading so well. Reading aloud catches nearly every one. Your eye will not.

7. The tense shift. A sentence starts in the past and drifts into the present halfway through.

• Wrong: She opened the file and realizes the data is gone.
• Right: She opened the file and realized the data was gone.

Present tense inside past narration is fine for general truths ("she learned that deadlines are suggestions"). Drift is different from choice, and readers can tell.

8. The misplaced "only." "Only" modifies whatever follows it, and dropping it in loose changes the claim.

• Wrong: I only edited the summary. (You did nothing but edit. You never saved or sent it.)
• Right: I edited only the summary. (The summary changed. Nothing else did.)

In speech, tone rescues you. On the page, nothing does.

9. "Whom" where "who" belongs. The object form whom is fading from everyday English, but the hypercorrected version is thriving.

• Wrong: Whom do you think will win?
• Right: Who do you think will win?

Answer the question mentally: "I think she will win." She, not her, so who, not whom.

10. "Then" for "than." Comparisons take than. Sequences take then.

• Wrong: We would rather ship late then ship broken.
• Right: We would rather ship late than ship broken.

One letter apart, constantly confused, invisible to spell checkers.

The damage table

The ranking is the point, so here it is at a glance:

Frequently Asked Questions

Do grammar checkers actually catch these?

Some of them, some of the time. A decent grammar checker flags subject-verb drift and many comma splices reliably. Homophone swaps usually sail through, because both forms are legal English. Use the checker as a tripwire and do the homophone pass by hand.

Should I try to fix all fifteen at once?

No. Nobody commits all fifteen; most writers rotate through two or three favorites for years. Identify your own repeats and hunt only those for a month. The list is a reference, not a to-do list.

Do these rules apply to casual writing?

Register changes the stakes, not the rules. Sloppy shorthand is fine in a group chat and fatal in a client proposal. The rankings above assume a document where a stranger is forming an impression of you, which covers almost all professional writing.

Is "whom" worth learning at all?

Yes, but as a small tool rather than a badge. "To whom it may concern" and "with whom" remain standard in formal writing. The larger credibility risk today runs the other direction: inserting whom where who belongs, which signals guessing.

Why do short documents get judged more harshly?

Because every sentence carries more of your reputation. One comma splice in a two-hundred-word cover letter dominates the reader's evidence. The same slip inside a fifty-page report is diluted past noticing. Short form, high stakes.