When do you use a dash? And why not a hyphen? The two marks serve different purposes, leaving many people puzzled.

The traditional dash is what some people refer to as the em dash. It is thicker and longer than the hyphen, often called the en dash. The dash separates information, whereas the hyphen is used most often to pull words together to modify another word, as in “That’s our top-selling product.”

Here’s a dash of clarity to help you distinguish the dash from the hyphen.

The dash is used for three reasons:

Emphasis – When you purposely want to accent information because it’s important and you want it to stick in the reader’s mind.
If you plan to submit a proposal–you only have until Frida—remember to mention the tech support we offer.

A sudden break in thought – I am looking forward to the meeting—I just finished the agenda—because it will be a great chance to hear from everyone.

Unusual information – When she began working out and eating a healthier diet, she felt better—her cholesterol dropped 45 points in six months.

People commonly use dashes and commas interchangeably. Almost anytime they want to pause, they insert a dash, but a comma is a routine pause; a dash is not.

Hyphens are shorter and thinner and are used to combine two words that function as one modifier (adjective) to describe something highspeed network, lowcost loans, New Hampshire’s firstinthenation presidential primary. The hyphens are appropriate, because in each case, both words are used in tandem. For example, we are not referring to a speed network, a high one versus a low one. The name of it is a high-speed network.

Don’t over hyphenate, because it makes for boring reading. The use of a comma often is a matter of judgment. If you think that in a given situation, you could omit the comma without confusing the reader, you can go without it. Here is a hint: read the sentence aloud, when you arrive at the two words you are hyphenating, if you hear your voice gain speed and squeeze the two words together, it is a signal that a hyphen is appropriate.