This section is meant to teach you how to predict when to use hyphens, but you can check out the Hyphens section of our Punctuation module for the basics.
Hyphens exist to connect one or more words. One reason that words need to be connected is to avoid confusion with compound modifiers. Compound modifiers are two or more modifiers that are supposed to work together to modify a noun. They work like this:
Compound Modifiers
[modifier - modifier] [noun]
There are two other ways that two or more modifiers can modify a noun:
Coordinate Adjectives
[modifier], [modifier] [noun]
Stacked Adjectives
[modifier [modifier [noun]]]
We cover the last two in the next section. For now, let's focus on Compound Modifiers, which are hyphenated (expect when they're not). Let's go over some compound modifiers and why they need to be hyphenated.
Why Hyphenate?
Consider the following list of multiple modifiers plus the nouns they modify:
high-quality + steak
middle-aged + man
half-baked + opinion
part-time + employee
cutting-edge + technology
Now, think about the modifiers as if they weren't connected. A half, baked opinion? So half of an opinion that's also baked? What?
Cutting edge technology? So edge technology...that's cutting? Steak that's high and quality? An aged man in the middle?
Okay, there's probably no one who actually makes those mistakes, but hyphens are more for organizational purposes anyway. Sure, you can still easily find The Goblet of Fire in your collection of Harry Potter books, but there's no harm in arranging them in chronological order anyway.
To review, if two or more modifiers work together to modify a noun that comes after them, hyphenate them.
If two or more modifiers each modify a noun separately and at the same time, put commas between them.
If multiple modifiers need to be in a certain order, don't put any punctuation.