A semi-colon is
A colon is
A semi-colon is used to connect two complete sentences that are connected in meaning.
I haven’t turned in that assignment yet; I was out sick last week.
You can also say:
I haven’t turned in that assignment yet because I was out sick last week.
A semi-colon is often a quick and easy way to repair a comma splice.
** (incorrect) I haven’t turned in that assignment yet, I was out sick last week.
A colon is used to introduce a part of a sentence that is not a complete sentence by itself. Three of the most common uses of the colon are:
a) To introduce a list of items:
Here are four ways to get people to buy our products: a good environment, good customer service, good promotions, and good advertising.
b) To introduce an example on the following line, as the teacher has done for the examples above.
c) To separate the subtitle of a book from the main title:
Pathways 4: Listening, Speaking and Critical Thinking