Hi! I'm trying to punctuate this sentence with either a semicolon or a colon. I cannot make it two separate sentences. It has to be one. Here's the sentence:
"This meeting has a special purpose: that is, it will provide on opportunity for our staff to become better acquainted."
I know that you would use a semicolon if the two sentences were related, but I was taught that you use a colon if the two sentences are very closely related. The second sentence is telling what the special purpose was. That is why I used a colon. Does anyone have any thoughts about this?

I'd leave the colon, and drop the 'that is'.
What do others think?

I agree. I would use the colon and drop the "that is" too. There is a section on this here.

Thank you for your opinions. Unfortunately, I cannot drop the "that is". I need to leave the sentence exactly as it is, but I need to insert either a semicolon or a colon. I have come to the conclusion to use the semicolon because that is the way this professor teaches. Thanks again for your help!

In that case, Robin, you have chosen the correct version. In your sentence, "that is" is known as a transitional phrase (i.e. it bridges the gap between two halves of the sentence). Transitional phrases are often preceded by semicolons. More common examples are: "however", "as a result" and "consequently".

Thanks Craig,

I ended up getting the answer correct