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10 common grammar mistakes (and how to fix them)

PT Phrasera Team · 6 min read · June 2026

Most grammar mistakes come from a handful of repeat offenders. Learn these ten and you’ll catch the majority of errors before anyone else does.

The usual suspects

  1. its vs it’sits is possessive; it’s = it is. “The dog wagged its tail.” “It’s raining.”
  2. your vs you’reyour is possessive; you’re = you are.
  3. there / their / they’re — place, possessive, “they are.”
  4. Comma splice — two full sentences joined by only a comma. Fix with a period, semicolon, or conjunction.
  5. Subject–verb agreement — “The list of items is long,” not are.
  6. affect vs effectaffect is usually a verb; effect usually a noun.
  7. then vs thanthen = time; than = comparison.
  8. Dangling modifiers — “Walking in, the lights were off” (who was walking?). Name the subject.
  9. Apostrophes for plurals1990s, not 1990’s; photos, not photo’s.
  10. Misused semicolons — join related full sentences, not a sentence and a fragment.

Catch them automatically

You don’t have to memorize every rule. Run your draft through the grammar checker — it flags grammar, spelling, punctuation and style issues, groups them by type, and shows a correctness score, in 28 languages. Accept the fixes you agree with; you stay in control.

Then read it once more

Tools catch most mechanical errors, but a final human read catches the rest — especially meaning-level slips no checker can see. Fix the ten above, lean on a checker, and read it aloud once. That combination beats either alone.

AI-powered — please review results before use.

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