Hyphens and Dashes

In the last lesson, we took a deeper look at commas. In this lesson, we will explore the difference between hyphens, en dashes, and em dashes. 

Hyphens

A hyphen connects two words that are closely related and are acting as a single word. For example:

• Two-thirds of survey respondents said they needed additional training.
• This number is toll-free. 

However, in some cases, you only connect the words with a hyphen when they are acting as an adjective modifying the word that follows them:

• This architecture supports high availability when traffic increases. (“availability” is a noun, and “high” is an adjective modifying it)
• To handle traffic spikes, design a high-availability architecture. (“high-availability” is a compound adjective modifying “architecture”)
• Next, you check in your files. (“check” is a verb, “in” is an adverb modifying “check”)
• The server sends a check-in notification. (“check-in” is a compound adjective modifying “notification”)

Words that are hyphenated often end up as open compounds (that is, they have a space instead of hyphen). “Open source” is an example of an open compound:

• This software is open source.
• This open source software is free to use. (No hyphen between "open" and "source")

And eventually, they may even become a single word. For example, "email" evolved like this:

Electronic mail -> e-mail -> email

“Log in” is still two words when it’s a verb:

• You can now log in to the application.

But it’s a single word when it acts as an adjective:

• Your login information was sent to your email address. 

Note: Why wouldn't you say "You can now log into the application"? Aren't you supposed to combine "in" and "to" when they're next to each other? In cases like "Look into this for me", the answer is yes. But in this example, "log in" is a phrasal verb, meaning that the verb "log" and the adverb "in" must go together and act as a single verb. Therefore, if you combined "in" and "to" to make "into", you would be splitting the "log in" phrasal verb in half, and "log" would be sad that "in" ran off with that scoundrel "to".

The Microsoft Manual of Style (and some other style guides) instructs us NOT to use hyphens after “-ly” adverbs:

• These are often-asked questions. 
• These are frequently asked questions. (No hyphen after an "-ly" adverb)

Irritating side note: Some grammar guides say you DO hyphenate after an “-ly” adverb IF the second word in the compound is the past participle. In this case, “frequently-asked questions” would require a hyphen, since “asked” is the past participle of the verb “to ask”, whereas “frequently upsetting incidents” would not use a hyphen, because "upsetting" is the present participle (not the past participle) of the verb "to upset". Confused? Don't be, because we’re going to ignore that stupid rule and stick with the Microsoft Manual of Style!

Dashes

There are two types of dashes: en dashes and em dashes. En dashes are longer than hyphens but shorter than em dashes.

-    hyphen
–   en dash
—  em dash

En dash
En dashes are uncommon. They connect two things that are related to each other by distance, essentially replacing the word “to”. For example:

• Take the San Francisco–New York flight.
• I read this in the May–September issue of the magazine.
• This certificate is valid 2017–2018.

Note: If you want to use "from" in the last example, use "to" instead of the en dash. For example:

• This certificate is valid from 2017 to 2018.

OR

• This certificate is valid 2017–2018.

But NOT:

• This certificate is valid from 2017–2018.

To type an en dash, see: https://www.howtotype.net/symbol/en-dash/

Em dash
The em dash is longer and is more common than the en dash. It sets off and emphasizes additional information in the sentence and can be used in place of commas, a colon, or parentheses—as I just did in this sentence. For example:

• When the car was finally delivered three months after it was ordered, she no longer wanted it.
• When the car was finally delivered, three months after it was ordered, she no longer wanted it.
• When the car was finally delivered—three months after it was ordered—she no longer wanted it. 

The second example uses commas to offset and emphasize the phrase. The third example uses em dashes to emphasize it even more, indicating how irritating it was that it took three months for the car to arrive.

Here's an example of an em dash replacing a colon:

• The white sand, the warm water, the sparkling sun—this is what brought them to Hawaii.

To type an em dash, see: https://www.howtotype.net/symbol/em-dash/

Summary

Hyphens connect two words that are closely related. En dashes connect two things that are related by time and replace the word "to". Em dashes set off a part of the sentence to give it extra emphasis. 

In the next lesson, we will look at coordinate vs. cumulative adjectives.

Additional resources

http://www.thepunctuationguide.com/hyphen-and-dashes.html