Proofreading your text for misspelled words and grammatical mistakes is essential. What about the punctuation, though?

Despite being more subtle, these errors can equally hurt your credibility. I’m going to point out six common punctuation errors that you shouldn’t be making, and give you examples so you’re sure about the right way to handle these situations.

Ready? Let’s go.

1. Apostrophe for Plurals

This mistake is particularly common among foreigners who are learning English as a second language. After all, you would expect native English speaks to know how to form plurals (right?). The apostrophe is used to form contractions (e.g., It’s time to go) and to indicate possession (e.g., Mary’s car is blue), but never to form plurals.

Wrong: The boy’s will go to the school tomorrow. Right: The boys will go to the school tomorrow.

2. The Comma Splice

When the comma is used to separate independent clauses, there must be a conjunction connecting them. If the conjunction is not there, we have a comma splice. You can fix this mistake by using a period instead of the comma, or by adding a coordinating conjunction.

Wrong: The car costs $10000, I am going to buy it. Right. The car costs $10000. I am going to buy it. Right: The car costs $10000, and I am going to buy it.

3. Quotation Marks for Emphasis

Quotation marks are mainly used to quote speech, sentences or words. They can also be used to denote irony. They can’t be used, however, to add emphasis to a word or sentence. It is not rare to find advertisements or promotional flyers carrying this error. If you want to add emphasis to a word, use the boldface type and not the quotation marks.

Wrong: This gift is “free”! Right: This gift is free!

4. Multiple Punctuation Marks

Unless you want to sound like an overly emotional teenager writing on MySpace, you should limit yourself to one exclamation point, regardless of how excited you might be when writing that sentence. The same applies to question marks and to the ellipsis (which should have only three dots). Also, keep in mind that exclamation points are not used that frequently in business and formal writing. If your text is loaded with them, you probably should review it.

Wrong: This is amazing!!!! Wrong: The man was silent…… Right: This is amazing! Right: The man was silent…

5. Punctuation Outside the Quotation Marks

If you are writing in American English, other punctuation should go inside the quotation marks, even if it is not part of the quotation itself. British English, on the other hand, places punctuation that is not part of the quoted sentence outside of the quotation marks.

Wrong in American English: Uncle John said, “My car is blue”. Right in American English: Uncle John said, “My car is blue.”

6. The Missing Comma After Introductory Elements

Sometimes you want to give an introduction or provide a background to a certain sentence. That is fine, but do not forget to place a comma after that introductory element. Notice that an introductory element can be a sentence (like in the example below) or a single word (e.g., however, moreover and so on).

Wrong: Before going to the school Joe stopped at my house. Right: Before going to the school, Joe stopped at my house.

What other punctuation mishaps do you make, or what drives you crazy when others fracture the rules?

Daniel Scocco is the editor of Daily Writing Tips. For more great advice on becoming a stronger writer, subscribe today.

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