This is the one rule to remember above all others to avoid making grammar mistakes. A hyphen should only be used when a participle is used in a compound adjective when you use the words before the noun you are describing. Because we’ve covered this a couple of times now, we’d like to put you to the test. Decide whether the following sentences are correct or not, and keep the key rule in your mind as you look:

1) The fast-acting medicine worked well.

2) The cars were incredibly fast-paced.

3) The beautiful-sounding birdsong broke out early in the morning.

Answers

1) Correct! We used the participle adjective before the noun!

2) Incorrect! The noun we are describing (the cars) comes before, so it should be ‘fast paced’ not ‘fast-paced’. Like this:

The cars were incredibly fast paced.

3) Correct! We used the noun after the compound adjective, so we should hyphenate in this situation.