Writers like to sprinkle their work with subordinate clauses because they add variety to sentence structure. A reading diet too heavy with simple sentences or even compound sentences becomes wearisome quickly. Subordinate clauses—also known as dependent clauses—used skillfully can add complexity and artfulness to writing.
A subordinate clause can either precede or follow its main clause. What writers tend to get confused about, however, is when and where to place commas in relation to subordinate clauses.
The simple rule is this: If a subordinate clause precedes the main clause, separate the two with a comma:
Unless you have a lot of money, steer clear of Rodeo Drive.
If the subordinate clause follows the main clause, no comma is usually needed:
Steer clear of Rodeo Drive unless you have a lot of money.
Many writers wouldn’t be able to resist the temptation to stick a comma between Drive and unless even though it’s not strictly necessary. There’s a natural pause that seems to call for a comma, but try to resist its call unless a pause is needed for special emphasis.
One notable exception is when the subordinating conjunction because is used and the main clause expresses a negative concept:
Don’t worry about your spelling errors because the editor will fix them.
Omitting a comma in this sentence suggests the meaning that there’s another reason not to worry about the spelling errors:
Don’t worry about your spelling errors because the editor will fix them; worry about them because you shouldn’t have made them to begin with.
So if the real reason you shouldn’t worry about the spelling errors is, in fact, because the editor will fix them, we need a comma:
Don’t worry about your spelling errors, because the editor will fix them.
Watch out for because in your subordinate clauses. Scrutinize your sentences to make sure you’re not clouding the issue and confusing your readers.