Use commas to separate introductory elements, nonessential clauses, and items in a series.

Rule: Introductory phrases keep the reader waiting for the main clause, so a comma marks that handoff. Nonessential clauses work differently: they interrupt a complete thought and should usually be set off on both sides.

• ACT often tests whether you can tell the difference between necessary identification and extra description. If the sentence would still point to the same person or thing without the clause, commas are usually needed.