Well, after the convention and some other issues, I am back.
Someone recently asked why a sentence inside of a sentence has to have dashes and not just commas. The answer is that, just as two sentences that have no conjunction between them cannot be connected by a comma, a sentence dropped into another sentence cannot just be surrounded by commas.
...He was thought to be younger than he appeared. I know you have heard this.
...He was thought -- I know you have heard this -- to be younger than he appeared.
And if the sentence that is dropped into the middle is asking a question, it has to have a question mark inside the dashes.
...He was thought -- have you heard this? -- to be younger than he appeared.
Happy punctuating!
Margie