Thoughtful Editing

When a clause is set off with commas, it is nonrestrictive—not crucial to the sentence meaning—and proper usage calls for which. “A battery-operated radio, which can be easily purchased, is useful during a power outage.” The rule of thumb: If the clause can be removed without losing the point of the sentence, use which. If the meaning of a sentence is altered when the clause is removed—indicating a restrictive clause—use that. “Any radio that runs on batteries is useful during a power outage.” Do not set off a restrictive clause with commas.