Concept 1

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

Core Idea

Use commas to show where the main sentence begins and which information is extra rather than essential.

Understanding

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.

Question

Worked Example

The writer has only one cousin named Elena. Which choice best punctuates the sentence?

"My cousin Elena who designs theater costumes volunteered to hem the robes."

Select an answer to see the explanation