English makes liberal use of punctuation marks. In fact, written English would hardly make sense if no punctuation marks were used. Here are some common mistakes in the use of punctuation marks.
1. A sentence must end with a full stop, a question mark or an exclamation mark.
• She is a lovely girl.
• Is that your sister?
• How sweet of you!
2. A new sentence that follows a question mark, a full stop or an exclamation mark has a capital letter.
INCORRECT: I looked out of the window. it was raining again.
CORRECT : I looked out of the window. It was raining again.
3. The punctuation mark should come immediately after the last letter of the word followed by a space.
INCORRECT: He is tall,dark and handsome.
CORRECT : He is tall, dark and handsome.
4. When you list items separate them with a comma. A comma is not usually used with and between the last two items unless these are long.
• I went to Thailand, Singapore, Malaysia and Hong Kong. (GB)
• I went to Thailand, Singapore, Malaysia, and Hong Kong. (US)
5. We do not put full stops, question marks or interrogation marks before or after grammatically incomplete sentences.
INCORRECT: I helped him. Because I liked him.
CORRECT : I helped him because I liked him.
6. A run-on sentence occurs when two sentence are incorrectly connected: the end of one sentence and the beginning of the next sentence are not properly marked by a period and a capital letter or by a semicolon.
INCORRECT: It was hot, therefore we went swimming.
CORRECT : It was hot; therefore, we went swimming.