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Clean Up Your Writing: Common Mistakes and How to Avoid Them

Like it or not, words, spelling, and punctuation can leave a lasting impression on others. However, even the most educated people often unknowingly make writing mistakes. Here are some examples of the most common grammar errors.

Confusing it’s and its.“It’s” is only ever used when short for “it is.” “Its” is a possessive that indicates something belonging to something that isn’t masculine or feminine (like “his” and “her,” but used when you’re not talking about a person). If it helps, remember that inanimate objects can’t really possess something in the way a human can. When in doubt, expand the word “its” to “it is” to see if it makes sense.

  • Incorrect: Its raining cats and dogs outside.
  • Correct: It’s raining cats and dogs outside.
  • Incorrect: The sofa looks great with it’s new cover.
  • Correct: The sofa looks great with its new cover.

You’re vs. Your.Even though “your” and “you’re” are homophones, there is a grammatical difference between these two forms. “You’re” is a contraction of you are. “Your” is a possessive adjective of you.  This grammatical disparity is the main difference between your and you’re.

  • Incorrect: Your beautiful.
  • Correct: You’re beautiful.
  • Incorrect: Do you know when your coming over?
  • Correct: Do you know when you’re coming over?

When to use Whom vs. Who. “Whom” should be used to refer to the object of a verb or preposition. When in doubt, try this simple trick: If you can replace the word with “he”’ or “’she,” use who. If you can replace it with “him” or “her,” use whom. “Who” should be used to refer to the subject of a sentence. Whom should be used to refer to the object of a verb or preposition.

  • Incorrect: Who shall I invite?
  • Correct: Whom shall I invite?
  • Incorrect: Whom is responsible?
  • Correct: Who is responsible?

Which and That. The battle over whether to use which or that is one many people struggle to get right. It’s a popular grammar question and most folks want a quick rule of thumb, but the choice is a bit nuanced. The test: If the sentence doesn’t need the clause that the word in question is connecting, use “which.” If it does, use “that.”

  • Incorrect: She wore the dress which suited her best.
  • Correct: She wore the dress that suited her best.
  • Incorrect: My dirt bike that is green goes really fast.
  • Correct: My dirt bike, which is green, goes really fast.

Superfluous Commas. It’s a common writing mistake to throw commas around liberally when they aren’t necessary. There are dozens of examples of this error, but here are a few common mistakes. A useful rule of thumb is to place commas where one makes a pause in speech.

  • Incorrect: The woman never went into the city, because she didn’t feel comfortable driving in traffic.
  • Correct: The woman never went into the city because she didn’t feel comfortable driving in traffic.
  • Incorrect: He wants to get a degree in political science, or communications.
  • Correct: He wants to get a degree in political science or communications.

No Comma in A Compound Sentence. A comma separates two or more independent clauses in a compound sentence separated by a conjunction, a word used to connect clauses or sentences or to coordinate words in the same clause.  The comma goes after the first clause and before the coordinating conjunction that separates the clauses.

  • Incorrect: The man jumped into a black sedan and he drove away before being noticed.
  • Correct: The man jumped into a black sedan, and he drove away before being noticed.
  • Incorrect: She was beautiful and she was happy and she was full of life.
  • Correct: She was beautiful, and she was happy, and she was full of life.

Misplaced Apostrophes. Apostrophesaren’t difficult to use once you know how, but putting them in the wrong place is one of the most common grammar mistakes in the English language. Many people use an apostrophe to form the plural of a word, particularly if the word in question ends in a vowel, which might make the word look strange with an “s” added to make it plural. Apostrophes indicate possession – something belonging to something or someone else. To indicate something belonging to one person, the apostrophe goes before the “s”.

  • Incorrect: The horse’s are in the field
  • CorrectThe horses are in the field.
  • Incorrect: In the 1980’s we liked hip hop.
  • Correct: In the 1980s we liked hip hop.

When to Spell Numerals and Figures. The general rule is to spell out numbers from zero to nine and use numerals from 10 and up. Like other rules of grammar, there are many exceptions to conveying numbers: age, addresses, years, phone numbers, etc. When in doubt, stick to the AP Style Guide for writing.

  • Incorrect: There are 8 soda cans in the refrigerator.
  • CorrectThere are eight soda cans in the refrigerator.
  • Incorrect: There are twelve cars in the parking lot.
  • Correct: There are 12 cars in the parking lot.


Susan Shelby, FSMPS, CPSM


Susan Shelby, FSMPS, CPSM, is the president and CEO of Rhino Public Relations, a full-service PR and marketing agency focused on meeting the unique needs of professional services firms. Rhino PR offers customized services based on each individual client’s goals and budget. Susan received the 2016 SMPS Boston Marketing Professional of the Year Award, which honors marketing excellence in the A/E/C industry. Follow her @RhinoPRBoston or visit for more information about how Rhino PR can help you take charge of your PR.

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