I NTRODUCTORY C LAUSES Longer prepositional phrases, in nitive phrases, or participial phrases that begin sentences or dependent clauses in introductory positions in sentences are often set o by commas In the best of times and in the worst of times, people look for help.” “When it snows, the child skis Just what constitutes longer phrases is a matter of judgment, and some writers feel safer setting o all introductory phrases with a