When we add a prefix to a verb, the resulting word may look like a very different word with a very different meaning than intended. We use a hyphen after the prefix to indicate which part is the prefix and which part is the main word. Consider this scenario.
We are leasing a house for 6 months. After 5 months, the owner sends us a letter asking whether we intend to stay in the house or vacate it. We want to stay in the house, so we communicate our intentions by letter. To our surprise, the owner starts showing the house to other people who may be interested in leasing it.
We confront the owner, asking why he is showing the house when we plan to stay. Once the confusion is resolved, he shows us what we wrote in the letter: “We plan to release the house when the current contract terminates.”
Release means let go and give freedom. This indicates that the house would be available for leasing because we would not be in it. What we wanted to communicate was that we would lease the house again. We should have written re-lease, meaning lease again. Without that hyphen, we communicated the opposite meaning.
If your car cover (the cover you place over your parked car to protect it from dust and hail) blows off, you will have to re-cover the car (cover again). But if your car is stolen, you will need to recover (find and claim something lost) it.
An undercoat of paint is paint under the surface layer, but under-coat the paint means not using enough paint.
The misconduct (bad conduct or bad behavior) of the audience can cause an orchestra leader to mis-conduct (to conduct incorrectly) the orchestra.
When you add a prefix to a verb, analyze the result. Have you written a different word? Will the reader know what part is the main word and what part is the prefix? If not, then you will probably need that hyphen. If the prefix is obvious, you need no comma.
This is the strategy for day 72 in 300 Days of Better Writing, available at Hostile Editing in PDF, Kindle, and paperback formats.
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