Top 10 Grammar Mistakes Part I

Are your grammar skills rusty? Are you one of the people who never liked English in the first place?
Help is available! Work on these common mistakes, and you’ll soon see a big improvement in your writing.
Here are Mistakes 1 – 5. (Click here to see Mistakes 6 – 10.)

1.  Not ending sentences with a period.
Here’s a quick lesson: Extra ideas end with commas.
Sentences end with periods.

When McKay asked for a backup, EXTRA IDEA
McKay asked for a backup. SENTENCE
While I was driving to the scene, EXTRA IDEA
I was driving to the scene. SENTENCE

Here’s how to put extra ideas and sentences together:

When McKay asked for a backup, Jackson responded. CORRECT
While I was driving to the scene, I had a flat tire. CORRECT

2.  Not knowing what a sentence is.
Here’s a quick lesson: A sentence begins with a person, place, or thing.

He ran out the door. SENTENCE
After he ran out the door, EXTRA IDEA

It’s a sentence even if it’s short or unclear.

I understand. SENTENCE
It is here. SENTENCE

For more help with commas, go to Commas Made Simple and study Rule 1.

3.  Using a comma to start a new sentence with it. Nope! Use a period.

The rope broke, it wasn’t strong enough.  INCORRECT
The rope broke. It wasn’t strong enough. CORRECT
I rejected her explanation, it didn’t make sense.  INCORRECT
I rejected her explanation. It didn’t make sense. CORRECT

4.  Getting pronouns mixed up (I, me, he, him, she, her, we, us, they, them).

Jim and me searched the neighborhood.  INCORRECT.
(Think: I searched the neighborhood.)
Jim and I searched the neighborhood. CORRECT

The captain gave Cynthia and I a special assignment.  INCORRECT
(Think: The captain gave me a special assignment.)
The captain gave Cynthia and me a special assignment. CORRECT

For more help with pronouns, go to Pronouns Made Simple and read Rule 3, “The Thumb Rule.”

5.  Using unnecessary apostrophes with the letter “s.”
Here’s a quick lesson: Use apostrophes only in contractions (don’t, can’t) and “of” ideas (Mary’s car, Tom’s schedule).
Apostrophes aren’t decorations, and they don’t mean more than one!

The cars will be replaced in two years. (no “of” ideas, and no apostrophes)  CORRECT
John’s laptop isn’t working properly. (laptop of John)  CORRECT
The Browns are taking a vacation next month. (no “of” ideas, and no apostrophes)
My uniform doesn’t need to be dry cleaned until next week. (don’t is a contraction)  CORRECT

For more help with apostrophes, go to About Apostrophes.
Need more help? Check out the resources at


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5 thoughts on “Top 10 Grammar Mistakes Part I

  1. Ashley Creason

    Should there be a period after bullet point #1? “Not ending a sentence with a period” is not a complete sentence; therefore, it should not have a period after it. Correct? The same would be true for the other #s.

  2. jdancer

    You have a sharp eye, Ashley – and you’ve raised a valid point. Technically there shouldn’t be a period after the bullet items. I made a kind of “executive decision” to use the periods anyway because they seemed to look more professional. Because bullets are associated with business writing, rather than academia, many writers say that it’s ok to be flexible about punctuating them. I’ve put myself in that camp.

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  4. Rogelio

    Can you explain this? I found this on another website.

    Since the sun and Earth are embedded in the galaxy. It is difficult for us to obtain an overall view of the galaxy.

    Since the sun and Earth are embedded in the galaxy, it is difficult for us to obtain an overall view of the galaxy.

    Thank you.

    1. Jean Post author

      Hi, Rogelio! Great question.
      Compare these two versions:
      1. “The sun and Earth are embedded in the galaxy”
      2. “Since the sun and Earth are embedded in the galaxy”

      #1 is a sentence. It ends with a period.
      #2 is an extra idea. It ends with a comma.

      Looking at the first word is a handy way to tell whether you have a sentence (which needs a period) or an extra idea (which needs a comma). Sentences usually begin with a person, place, or thing.

      Try these:
      1. Because I like pizza
      2. I like pizza

      “Because” isn’t a person, place, or thing. So you know that #1 is an extra idea. It needs to be attached to a sentence. “Because I like pizza, I go to the Bistro every weekend.”

      I’m going to email you a handout that gives more examples. Please write me back if you have more questions! Jean


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