ACT English punctuation: complete overview of commas, apostrophes, colons and semicolons, dashes, end marks, and the recurring traps

Punctuation is a large part of the Conventions of Standard English category, which is more than half the ACT English section, so it carries a lot of points, and most of them come down to a small set of rules and traps. This site breaks the area into six dot points. This overview maps them, shows the common thread (every mark must do a job), and explains how to study them.

The six punctuation skills

Each skill is part of punctuating sentences correctly.

• Commas and unnecessary commas. The four comma jobs and the unnecessary commas the ACT plants. See commas and unnecessary commas.
• Apostrophes and possessives. Possession, contractions, its versus it's, and plain plurals. See apostrophes and possessives.
• Colons and semicolons. What must come before each, and join versus introduce. See colons and semicolons.
• Dashes and parentheses. Matching pairs for nonessential elements and the single introducing dash. See dashes and parentheses.
• End punctuation and question marks. Period versus question mark, and the indirect question. See end punctuation and question marks.
• Common punctuation traps. The recurring planted errors and a single defense strategy. See common punctuation traps.

The thread through every skill: every mark needs a job

The organizing idea is that punctuation is functional: a comma, semicolon, colon, dash, or end mark must perform a defined job, and a mark doing no job is wrong. Commas have four jobs; semicolons and colons both need a complete clause before them; paired marks must match; and an end mark depends on whether the whole sentence asks something. The traps the ACT reuses are nearly all extra marks, especially the comma between a subject and its verb, so the strongest single habit is to demand a job for every mark and, among correct options, prefer the one with no unjustified punctuation.

How the items are tested

• Underlined-portion questions: a punctuation mark (or its absence) is underlined, and four options vary the punctuation. You choose the version that follows the rule.
• Overlap with sentence structure: run-ons, comma splices, and the semicolon join are shared with the sentence-structure module, so the same logic recurs.
• Least-punctuation tiebreaker: when options differ only in how many marks they add, the leanest correct option usually wins.

How to study ACT punctuation

1. Learn the four comma jobs and refuse any comma that does not do one of them, especially the subject-verb comma.
2. Drill the apostrophe decision tree: possession, contraction, or plain plural, with the expand-the-contraction test for its and it's.
3. Memorize the shared colon and semicolon rule: a complete clause before the mark.
4. Match paired marks (commas, dashes, parentheses) and spot the single introducing dash.
5. Classify the sentence before choosing an end mark, and watch for indirect questions.
6. Default to "leave it out" when a mark has no clear job.

For the official exam materials

ACT, Inc. publishes the English test description and free official practice. See the description of the ACT English test and the test preparation page. Always study from the current official materials, because the question style is set by ACT.