Commas and Semicolons

• Use the boundary test on marks that join or introduce: split the sentence at a period, semicolon, colon, single dash, or comma + FANBOYS and ask whether each side is a complete thought (period, semicolon, comma + FANBOYS need two complete sides). Commas inside one clause are not judged by this test; they need a named reason
• Spot a comma splice (two independent clauses joined by only a comma) and fix it
• Apply the comma rules the ACT tests (lists, introductory elements, nonessential information, compound sentences) and the no-comma rules, give every comma a reason you can name, and run a quick removable-or-not round before placing commas
• Use a colon or a single dash only after a complete thought, and set off removable information with a matching pair of dashes, just as with a pair of commas
• Finish on one ACT-hard question and say what made it hard

The single most-tested ACT punctuation skill is deciding whether the boundary between two clauses is punctuated correctly, so start there. (On lists: the ACT does not test the serial comma. 'red, white and blue' and 'red, white, and blue' are both acceptable, so never mark either one wrong; ACT list items differ in some other way.) There are three standard ways to join two independent clauses: (1) a period, (2) a semicolon, and (3) a comma plus a FANBOYS coordinating conjunction (for, and, nor, but, or, yet, so). A comma alone between two independent clauses is a comma splice and is always wrong (this connects directly to the run-on and comma-splice work in the Sentence Structure lesson). Because a semicolon is essentially equivalent to a period here, a useful elimination shortcut is that if one choice uses a semicolon and another uses a period and capital letter between the same two clauses, neither can be the answer: they are equally correct, and the ACT never has two correct answers, so the key is a choice that differs in some other way. Commas are tested heavily: use them after introductory phrases (introductory means before the main clause; a phrase that trails the main clause, as in 'The game was canceled due to rain,' usually takes no comma), around nonessential (parenthetical) information, between items in a list, and before a coordinating conjunction (FANBOYS) that joins two independent clauses. The ACT often tests whether you know the difference between essential and nonessential clauses. Information is nonessential, and needs a comma on both sides, when the noun is already identified without it; removing it never means checking that the rest is still a sentence (remove the subject itself and nothing is left). The test is whether the noun is already identified without the phrase, not whether the sentence still reads as a sentence: in 'The book about climate change was riveting' the phrase tells which book, so it is essential and takes no commas, while in 'My first novel, about climate change, took six years' the phrase adds information about a book already identified, so it takes a pair. When the passage does not settle which reading is meant, the answer choices will: the ACT never makes both correct. Just as important is the no-comma rule: never place a single comma between a subject and its verb, or between a verb and its object ('The runner who trained all summer, won' is wrong). When you see a comma, confirm it is doing a real job; if you cannot name the rule it follows, it is probably an unnecessary comma. Top-score comma cases: (1) an appositive that identifies which one takes no commas ('the novelist Toni Morrison'), while one that adds information about a noun already identified takes a pair ('my only sister, Ana, lives in Ohio'); (2) a separate rule from the subject-verb and verb-object rule: no comma before 'and' when it joins two verbs that share one subject ('She finished the draft and sent it to her editor'), because the comma goes before 'and' only when a new subject and verb follow; (3) a clause that begins with 'that' is essential and takes no commas, while a 'which' clause set off by commas is nonessential; (4) no comma between an adjective and its noun, and none directly after 'such as' or 'including'; (5) two adjectives take a comma between them only if 'and' could replace it ('a cold, dark night' works as 'a cold and dark night,' but 'a heavy wool coat' takes no comma because 'a heavy and wool coat' does not work). The boundary test is for marks that join or introduce (a period, a semicolon, a comma plus FANBOYS, a colon, a single dash): split the sentence at the mark and ask whether each side is a complete thought. A period, a semicolon, and a comma plus FANBOYS need a complete thought on both sides. A colon, and a single dash used the same way, need a complete thought before the mark; what follows can be a list, a phrase, or a clause that explains ('She had one goal: finish the race'). Any other spot takes a comma or no mark, and every comma needs a reason you can name. The split test does not decide those commas: a comma that closes a nonessential clause is required even though the words after it are not a complete sentence ('The orchestra, which had practiced for weeks, was ready' needs the comma after 'weeks' to close the pair), so never reject a comma just because one side is incomplete. So 'The reasons were: cost and time' is wrong, because 'The reasons were' is not complete. A pair of dashes works like a pair of commas around removable information, and the two marks must match: an interruption that opens with a dash closes with a dash, not a comma. Apostrophes are taught in the Pronouns lesson, and the Apostrophes, Colons, and Dashes lesson adds parentheses and more practice. The ACT-hard version: a choice fixes a comma splice with a colon when the first side is not complete, or an interruption opens with a dash and closes with a comma.

• If you see a semicolon in an answer choice, check that both sides are independent clauses. If not, the semicolon is wrong.
• If you cannot name the rule a comma is following, take the comma out.
• Before a colon, cover everything after it. What is left must be a complete sentence, or the colon is wrong.
• When in doubt between a comma and no comma, check if the information is essential to identifying the noun. If so, no comma.