THE PARENTHESES:

Use parentheses to enclose information that clarifies or is used as an aside.

He gave me a check for my birthday ($100).

Periods go inside parentheses only if an entire sentence is inside the parentheses.

Please read the book. (You’ll be astounded.)

THE EM DASH:

The em dash is the most versatile of all punctuation marks. It can be used instead of commas, semicolons, parentheses, or quotation marks. 

The em dash (—) sets off a word or clause and adds emphasis. Or, it can signal either an interruption or amplification of an idea.

You can put a space on both sides of it, as found in most newspapers, or leave a space following it. What matters is that you are consistent—throughout your article or book—to do it the same way each time. 

The em dash provides a more casual tone and look than a semicolon.

It can also be used to substitute for a missing word or words, such as swear words. However, personally, I use the ellipses (…) for this purpose.

Em dashes are also used as interruptors in sentences—mostly in blogs and digital content—to add a casual and conversational tone when writing online. They can be used to insert commentary on what is written, add a short joke or witty comment, or to add an example to your information. 

So, is there a battle going on between the parenthesis and the em dash? Perhaps even the semi-colon?

There doesn’t have to be.

Use whatever you are most comfortable with—but don’t overdo the use of any particular punctuation. They disrupt the reader’s train of thought.

And—they—can—be—annoying!

A sprinkling here and there are permissible. And, authors often find using them to help with the flow of ideas when writing. 

Inquiring minds want to know:  Why is it called the “em dash”? It is the width of the letter M.